[v9,41/43] virt: Add SEV-SNP guest driver

SEV-SNP specification provides the guest a mechanism to communicate with
the PSP without risk from a malicious hypervisor who wishes to read, alter,
drop or replay the messages sent. The driver uses snp_issue_guest_request()
to issue GHCB SNP_GUEST_REQUEST or SNP_EXT_GUEST_REQUEST NAE events to
submit the request to PSP.

The PSP requires that all communication should be encrypted using key
specified through the platform_data.

The userspace can use SNP_GET_REPORT ioctl() to query the guest
attestation report.

See SEV-SNP spec section Guest Messages for more details.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 Documentation/virt/coco/sevguest.rst  |  81 ++++
 drivers/virt/Kconfig                  |   3 +
 drivers/virt/Makefile                 |   1 +
 drivers/virt/coco/sevguest/Kconfig    |  12 +
 drivers/virt/coco/sevguest/Makefile   |   2 +
 drivers/virt/coco/sevguest/sevguest.c | 605 ++++++++++++++++++++++++++
 drivers/virt/coco/sevguest/sevguest.h |  98 +++++
 include/uapi/linux/sev-guest.h        |  50 +++
 8 files changed, 852 insertions(+)
 create mode 100644 Documentation/virt/coco/sevguest.rst
 create mode 100644 drivers/virt/coco/sevguest/Kconfig
 create mode 100644 drivers/virt/coco/sevguest/Makefile
 create mode 100644 drivers/virt/coco/sevguest/sevguest.c
 create mode 100644 drivers/virt/coco/sevguest/sevguest.h
 create mode 100644 include/uapi/linux/sev-guest.h

On Fri, Jan 28, 2022 at 10:19 AM Brijesh Singh <brijesh.singh@amd.com> wrote:
>
> SEV-SNP specification provides the guest a mechanism to communicate with
> the PSP without risk from a malicious hypervisor who wishes to read, alter,
> drop or replay the messages sent. The driver uses snp_issue_guest_request()
> to issue GHCB SNP_GUEST_REQUEST or SNP_EXT_GUEST_REQUEST NAE events to
> submit the request to PSP.
>
> The PSP requires that all communication should be encrypted using key
> specified through the platform_data.
>
> The userspace can use SNP_GET_REPORT ioctl() to query the guest
> attestation report.
>
> See SEV-SNP spec section Guest Messages for more details.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>

Reviewed-by: Peter Gonda <pgonda@google.com>

I'll try and do some basic functionality testing done with this later.

> ---
>  Documentation/virt/coco/sevguest.rst  |  81 ++++
>  drivers/virt/Kconfig                  |   3 +
>  drivers/virt/Makefile                 |   1 +
>  drivers/virt/coco/sevguest/Kconfig    |  12 +
>  drivers/virt/coco/sevguest/Makefile   |   2 +
>  drivers/virt/coco/sevguest/sevguest.c | 605 ++++++++++++++++++++++++++
>  drivers/virt/coco/sevguest/sevguest.h |  98 +++++
>  include/uapi/linux/sev-guest.h        |  50 +++
>  8 files changed, 852 insertions(+)
>  create mode 100644 Documentation/virt/coco/sevguest.rst
>  create mode 100644 drivers/virt/coco/sevguest/Kconfig
>  create mode 100644 drivers/virt/coco/sevguest/Makefile
>  create mode 100644 drivers/virt/coco/sevguest/sevguest.c
>  create mode 100644 drivers/virt/coco/sevguest/sevguest.h
>  create mode 100644 include/uapi/linux/sev-guest.h
>
> diff --git a/Documentation/virt/coco/sevguest.rst b/Documentation/virt/coco/sevguest.rst
> new file mode 100644
> index 000000000000..47ef3b0821d5
> --- /dev/null
> +++ b/Documentation/virt/coco/sevguest.rst
> @@ -0,0 +1,81 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +===================================================================
> +The Definitive SEV Guest API Documentation
> +===================================================================
> +
> +1. General description
> +======================
> +
> +The SEV API is a set of ioctls that are used by the guest or hypervisor
> +to get or set certain aspect of the SEV virtual machine. The ioctls belong
> +to the following classes:
> +
> + - Hypervisor ioctls: These query and set global attributes which affect the
> +   whole SEV firmware.  These ioctl are used by platform provision tools.
> +
> + - Guest ioctls: These query and set attributes of the SEV virtual machine.
> +
> +2. API description
> +==================
> +
> +This section describes ioctls that can be used to query or set SEV guests.
> +For each ioctl, the following information is provided along with a
> +description:
> +
> +  Technology:
> +      which SEV technology provides this ioctl. sev, sev-es, sev-snp or all.
> +
> +  Type:
> +      hypervisor or guest. The ioctl can be used inside the guest or the
> +      hypervisor.
> +
> +  Parameters:
> +      what parameters are accepted by the ioctl.
> +
> +  Returns:
> +      the return value.  General error numbers (ENOMEM, EINVAL)
> +      are not detailed, but errors with specific meanings are.
> +
> +The guest ioctl should be issued on a file descriptor of the /dev/sev-guest device.
> +The ioctl accepts struct snp_user_guest_request. The input and output structure is
> +specified through the req_data and resp_data field respectively. If the ioctl fails
> +to execute due to a firmware error, then fw_err code will be set otherwise the
> +fw_err will be set to 0xff.
> +
> +::
> +        struct snp_guest_request_ioctl {
> +                /* Message version number */
> +                __u32 msg_version;
> +
> +                /* Request and response structure address */
> +                __u64 req_data;
> +                __u64 resp_data;
> +
> +                /* firmware error code on failure (see psp-sev.h) */
> +                __u64 fw_err;
> +        };
> +
> +2.1 SNP_GET_REPORT
> +------------------
> +
> +:Technology: sev-snp
> +:Type: guest ioctl
> +:Parameters (in): struct snp_report_req
> +:Returns (out): struct snp_report_resp on success, -negative on error
> +
> +The SNP_GET_REPORT ioctl can be used to query the attestation report from the
> +SEV-SNP firmware. The ioctl uses the SNP_GUEST_REQUEST (MSG_REPORT_REQ) command
> +provided by the SEV-SNP firmware to query the attestation report.
> +
> +On success, the snp_report_resp.data will contains the report. The report
> +contain the format described in the SEV-SNP specification. See the SEV-SNP
> +specification for further details.
> +
> +
> +Reference
> +---------
> +
> +SEV-SNP and GHCB specification: developer.amd.com/sev
> +
> +The driver is based on SEV-SNP firmware spec 0.9 and GHCB spec version 2.0.
> diff --git a/drivers/virt/Kconfig b/drivers/virt/Kconfig
> index 8061e8ef449f..e457e47610d3 100644
> --- a/drivers/virt/Kconfig
> +++ b/drivers/virt/Kconfig
> @@ -36,4 +36,7 @@ source "drivers/virt/vboxguest/Kconfig"
>  source "drivers/virt/nitro_enclaves/Kconfig"
>
>  source "drivers/virt/acrn/Kconfig"
> +
> +source "drivers/virt/coco/sevguest/Kconfig"
> +
>  endif
> diff --git a/drivers/virt/Makefile b/drivers/virt/Makefile
> index 3e272ea60cd9..9c704a6fdcda 100644
> --- a/drivers/virt/Makefile
> +++ b/drivers/virt/Makefile
> @@ -8,3 +8,4 @@ obj-y                           += vboxguest/
>
>  obj-$(CONFIG_NITRO_ENCLAVES)   += nitro_enclaves/
>  obj-$(CONFIG_ACRN_HSM)         += acrn/
> +obj-$(CONFIG_SEV_GUEST)                += coco/sevguest/
> diff --git a/drivers/virt/coco/sevguest/Kconfig b/drivers/virt/coco/sevguest/Kconfig
> new file mode 100644
> index 000000000000..07ab9ec6471c
> --- /dev/null
> +++ b/drivers/virt/coco/sevguest/Kconfig
> @@ -0,0 +1,12 @@
> +config SEV_GUEST
> +       tristate "AMD SEV Guest driver"
> +       default y
> +       depends on AMD_MEM_ENCRYPT && CRYPTO_AEAD2
> +       help
> +         SEV-SNP firmware provides the guest a mechanism to communicate with
> +         the PSP without risk from a malicious hypervisor who wishes to read,
> +         alter, drop or replay the messages sent. The driver provides
> +         userspace interface to communicate with the PSP to request the
> +         attestation report and more.
> +
> +         If you choose 'M' here, this module will be called sevguest.
> diff --git a/drivers/virt/coco/sevguest/Makefile b/drivers/virt/coco/sevguest/Makefile
> new file mode 100644
> index 000000000000..b1ffb2b4177b
> --- /dev/null
> +++ b/drivers/virt/coco/sevguest/Makefile
> @@ -0,0 +1,2 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +obj-$(CONFIG_SEV_GUEST) += sevguest.o
> diff --git a/drivers/virt/coco/sevguest/sevguest.c b/drivers/virt/coco/sevguest/sevguest.c
> new file mode 100644
> index 000000000000..6dc0785ddd4b
> --- /dev/null
> +++ b/drivers/virt/coco/sevguest/sevguest.c
> @@ -0,0 +1,605 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * AMD Secure Encrypted Virtualization Nested Paging (SEV-SNP) guest request interface
> + *
> + * Copyright (C) 2021 Advanced Micro Devices, Inc.
> + *
> + * Author: Brijesh Singh <brijesh.singh@amd.com>
> + */
> +
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/types.h>
> +#include <linux/mutex.h>
> +#include <linux/io.h>
> +#include <linux/platform_device.h>
> +#include <linux/miscdevice.h>
> +#include <linux/set_memory.h>
> +#include <linux/fs.h>
> +#include <crypto/aead.h>
> +#include <linux/scatterlist.h>
> +#include <linux/psp-sev.h>
> +#include <uapi/linux/sev-guest.h>
> +#include <uapi/linux/psp-sev.h>
> +
> +#include <asm/svm.h>
> +#include <asm/sev.h>
> +
> +#include "sevguest.h"
> +
> +#define DEVICE_NAME    "sev-guest"
> +#define AAD_LEN                48
> +#define MSG_HDR_VER    1
> +
> +struct snp_guest_crypto {
> +       struct crypto_aead *tfm;
> +       u8 *iv, *authtag;
> +       int iv_len, a_len;
> +};
> +
> +struct snp_guest_dev {
> +       struct device *dev;
> +       struct miscdevice misc;
> +
> +       struct snp_guest_crypto *crypto;
> +       struct snp_guest_msg *request, *response;
> +       struct snp_secrets_page_layout *layout;
> +       struct snp_req_data input;
> +       u32 *os_area_msg_seqno;
> +       u8 *vmpck;
> +};
> +
> +static u32 vmpck_id;
> +module_param(vmpck_id, uint, 0444);
> +MODULE_PARM_DESC(vmpck_id, "The VMPCK ID to use when communicating with the PSP.");
> +
> +static DEFINE_MUTEX(snp_cmd_mutex);
> +
> +static bool is_vmpck_empty(struct snp_guest_dev *snp_dev)
> +{
> +       char zero_key[VMPCK_KEY_LEN] = {0};
> +
> +       if (snp_dev->vmpck)
> +               return memcmp(snp_dev->vmpck, zero_key, VMPCK_KEY_LEN) == 0;
> +
> +       return true;
> +}
> +
> +static void snp_disable_vmpck(struct snp_guest_dev *snp_dev)
> +{
> +       memzero_explicit(snp_dev->vmpck, VMPCK_KEY_LEN);
> +       snp_dev->vmpck = NULL;
> +}
> +
> +static inline u64 __snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
> +{
> +       u64 count;
> +
> +       lockdep_assert_held(&snp_cmd_mutex);
> +
> +       /* Read the current message sequence counter from secrets pages */
> +       count = *snp_dev->os_area_msg_seqno;
> +
> +       return count + 1;
> +}
> +
> +/* Return a non-zero on success */
> +static u64 snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
> +{
> +       u64 count = __snp_get_msg_seqno(snp_dev);
> +
> +       /*
> +        * The message sequence counter for the SNP guest request is a  64-bit
> +        * value but the version 2 of GHCB specification defines a 32-bit storage
> +        * for it. If the counter exceeds the 32-bit value then return zero.
> +        * The caller should check the return value, but if the caller happens to
> +        * not check the value and use it, then the firmware treats zero as an
> +        * invalid number and will fail the  message request.
> +        */
> +       if (count >= UINT_MAX) {
> +               pr_err_ratelimited("SNP guest request message sequence counter overflow\n");
> +               return 0;
> +       }
> +
> +       return count;
> +}
> +
> +static void snp_inc_msg_seqno(struct snp_guest_dev *snp_dev)
> +{
> +       /*
> +        * The counter is also incremented by the PSP, so increment it by 2
> +        * and save in secrets page.
> +        */
> +       *snp_dev->os_area_msg_seqno += 2;
> +}
> +
> +static inline struct snp_guest_dev *to_snp_dev(struct file *file)
> +{
> +       struct miscdevice *dev = file->private_data;
> +
> +       return container_of(dev, struct snp_guest_dev, misc);
> +}
> +
> +static struct snp_guest_crypto *init_crypto(struct snp_guest_dev *snp_dev, u8 *key, size_t keylen)
> +{
> +       struct snp_guest_crypto *crypto;
> +
> +       crypto = kzalloc(sizeof(*crypto), GFP_KERNEL_ACCOUNT);
> +       if (!crypto)
> +               return NULL;
> +
> +       crypto->tfm = crypto_alloc_aead("gcm(aes)", 0, 0);
> +       if (IS_ERR(crypto->tfm))
> +               goto e_free;
> +
> +       if (crypto_aead_setkey(crypto->tfm, key, keylen))
> +               goto e_free_crypto;
> +
> +       crypto->iv_len = crypto_aead_ivsize(crypto->tfm);
> +       if (crypto->iv_len < 12) {
> +               dev_err(snp_dev->dev, "IV length is less than 12.\n");
> +               goto e_free_crypto;
> +       }
> +
> +       crypto->iv = kmalloc(crypto->iv_len, GFP_KERNEL_ACCOUNT);
> +       if (!crypto->iv)
> +               goto e_free_crypto;
> +
> +       if (crypto_aead_authsize(crypto->tfm) > MAX_AUTHTAG_LEN) {
> +               if (crypto_aead_setauthsize(crypto->tfm, MAX_AUTHTAG_LEN)) {
> +                       dev_err(snp_dev->dev, "failed to set authsize to %d\n", MAX_AUTHTAG_LEN);
> +                       goto e_free_crypto;
> +               }
> +       }
> +
> +       crypto->a_len = crypto_aead_authsize(crypto->tfm);
> +       crypto->authtag = kmalloc(crypto->a_len, GFP_KERNEL_ACCOUNT);
> +       if (!crypto->authtag)
> +               goto e_free_crypto;
> +
> +       return crypto;
> +
> +e_free_crypto:
> +       crypto_free_aead(crypto->tfm);
> +e_free:
> +       kfree(crypto->iv);
> +       kfree(crypto->authtag);
> +       kfree(crypto);
> +
> +       return NULL;
> +}
> +
> +static void deinit_crypto(struct snp_guest_crypto *crypto)
> +{
> +       crypto_free_aead(crypto->tfm);
> +       kfree(crypto->iv);
> +       kfree(crypto->authtag);
> +       kfree(crypto);
> +}
> +
> +static int enc_dec_message(struct snp_guest_crypto *crypto, struct snp_guest_msg *msg,
> +                          u8 *src_buf, u8 *dst_buf, size_t len, bool enc)
> +{
> +       struct snp_guest_msg_hdr *hdr = &msg->hdr;
> +       struct scatterlist src[3], dst[3];
> +       DECLARE_CRYPTO_WAIT(wait);
> +       struct aead_request *req;
> +       int ret;
> +
> +       req = aead_request_alloc(crypto->tfm, GFP_KERNEL);
> +       if (!req)
> +               return -ENOMEM;
> +
> +       /*
> +        * AEAD memory operations:
> +        * +------ AAD -------+------- DATA -----+---- AUTHTAG----+
> +        * |  msg header      |  plaintext       |  hdr->authtag  |
> +        * | bytes 30h - 5Fh  |    or            |                |
> +        * |                  |   cipher         |                |
> +        * +------------------+------------------+----------------+
> +        */
> +       sg_init_table(src, 3);
> +       sg_set_buf(&src[0], &hdr->algo, AAD_LEN);
> +       sg_set_buf(&src[1], src_buf, hdr->msg_sz);
> +       sg_set_buf(&src[2], hdr->authtag, crypto->a_len);
> +
> +       sg_init_table(dst, 3);
> +       sg_set_buf(&dst[0], &hdr->algo, AAD_LEN);
> +       sg_set_buf(&dst[1], dst_buf, hdr->msg_sz);
> +       sg_set_buf(&dst[2], hdr->authtag, crypto->a_len);
> +
> +       aead_request_set_ad(req, AAD_LEN);
> +       aead_request_set_tfm(req, crypto->tfm);
> +       aead_request_set_callback(req, 0, crypto_req_done, &wait);
> +
> +       aead_request_set_crypt(req, src, dst, len, crypto->iv);
> +       ret = crypto_wait_req(enc ? crypto_aead_encrypt(req) : crypto_aead_decrypt(req), &wait);
> +
> +       aead_request_free(req);
> +       return ret;
> +}
> +
> +static int __enc_payload(struct snp_guest_dev *snp_dev, struct snp_guest_msg *msg,
> +                        void *plaintext, size_t len)
> +{
> +       struct snp_guest_crypto *crypto = snp_dev->crypto;
> +       struct snp_guest_msg_hdr *hdr = &msg->hdr;
> +
> +       memset(crypto->iv, 0, crypto->iv_len);
> +       memcpy(crypto->iv, &hdr->msg_seqno, sizeof(hdr->msg_seqno));
> +
> +       return enc_dec_message(crypto, msg, plaintext, msg->payload, len, true);
> +}
> +
> +static int dec_payload(struct snp_guest_dev *snp_dev, struct snp_guest_msg *msg,
> +                      void *plaintext, size_t len)
> +{
> +       struct snp_guest_crypto *crypto = snp_dev->crypto;
> +       struct snp_guest_msg_hdr *hdr = &msg->hdr;
> +
> +       /* Build IV with response buffer sequence number */
> +       memset(crypto->iv, 0, crypto->iv_len);
> +       memcpy(crypto->iv, &hdr->msg_seqno, sizeof(hdr->msg_seqno));
> +
> +       return enc_dec_message(crypto, msg, msg->payload, plaintext, len, false);
> +}
> +
> +static int verify_and_dec_payload(struct snp_guest_dev *snp_dev, void *payload, u32 sz)
> +{
> +       struct snp_guest_crypto *crypto = snp_dev->crypto;
> +       struct snp_guest_msg *resp = snp_dev->response;
> +       struct snp_guest_msg *req = snp_dev->request;
> +       struct snp_guest_msg_hdr *req_hdr = &req->hdr;
> +       struct snp_guest_msg_hdr *resp_hdr = &resp->hdr;
> +
> +       dev_dbg(snp_dev->dev, "response [seqno %lld type %d version %d sz %d]\n",
> +               resp_hdr->msg_seqno, resp_hdr->msg_type, resp_hdr->msg_version, resp_hdr->msg_sz);
> +
> +       /* Verify that the sequence counter is incremented by 1 */
> +       if (unlikely(resp_hdr->msg_seqno != (req_hdr->msg_seqno + 1)))
> +               return -EBADMSG;
> +
> +       /* Verify response message type and version number. */
> +       if (resp_hdr->msg_type != (req_hdr->msg_type + 1) ||
> +           resp_hdr->msg_version != req_hdr->msg_version)
> +               return -EBADMSG;
> +
> +       /*
> +        * If the message size is greater than our buffer length then return
> +        * an error.
> +        */
> +       if (unlikely((resp_hdr->msg_sz + crypto->a_len) > sz))
> +               return -EBADMSG;
> +
> +       /* Decrypt the payload */
> +       return dec_payload(snp_dev, resp, payload, resp_hdr->msg_sz + crypto->a_len);
> +}
> +
> +static bool enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8 type,
> +                       void *payload, size_t sz)
> +{
> +       struct snp_guest_msg *req = snp_dev->request;
> +       struct snp_guest_msg_hdr *hdr = &req->hdr;
> +
> +       memset(req, 0, sizeof(*req));
> +
> +       hdr->algo = SNP_AEAD_AES_256_GCM;
> +       hdr->hdr_version = MSG_HDR_VER;
> +       hdr->hdr_sz = sizeof(*hdr);
> +       hdr->msg_type = type;
> +       hdr->msg_version = version;
> +       hdr->msg_seqno = seqno;
> +       hdr->msg_vmpck = vmpck_id;
> +       hdr->msg_sz = sz;
> +
> +       /* Verify the sequence number is non-zero */
> +       if (!hdr->msg_seqno)
> +               return -ENOSR;
> +
> +       dev_dbg(snp_dev->dev, "request [seqno %lld type %d version %d sz %d]\n",
> +               hdr->msg_seqno, hdr->msg_type, hdr->msg_version, hdr->msg_sz);
> +
> +       return __enc_payload(snp_dev, req, payload, sz);
> +}
> +
> +static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, int msg_ver,
> +                               u8 type, void *req_buf, size_t req_sz, void *resp_buf,
> +                               u32 resp_sz, __u64 *fw_err)
> +{
> +       unsigned long err;
> +       u64 seqno;
> +       int rc;
> +
> +       /* Get message sequence and verify that its a non-zero */
> +       seqno = snp_get_msg_seqno(snp_dev);
> +       if (!seqno)
> +               return -EIO;
> +
> +       memset(snp_dev->response, 0, sizeof(*snp_dev->response));
> +
> +       /* Encrypt the userspace provided payload */
> +       rc = enc_payload(snp_dev, seqno, msg_ver, type, req_buf, req_sz);
> +       if (rc)
> +               return rc;
> +
> +       /* Call firmware to process the request */
> +       rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);
> +       if (fw_err)
> +               *fw_err = err;

All the other pointers are required. Why not require this one to make
it simpler?

> +
> +       if (rc)
> +               return rc;
> +
> +       rc = verify_and_dec_payload(snp_dev, resp_buf, resp_sz);
> +       if (rc) {
> +               /*
> +                * The verify_and_dec_payload() will fail only if the hypervisor is
> +                * actively modifying the message header or corrupting the encrypted payload.
> +                * This hints that hypervisor is acting in a bad faith. Disable the VMPCK so that
> +                * the key cannot be used for any communication. The key is disabled to ensure
> +                * that AES-GCM does not use the same IV while encrypting the request payload.
> +                */
> +               dev_alert(snp_dev->dev,
> +                         "Detected unexpected decode failure, disabling the vmpck_id %d\n",
> +                         vmpck_id);
> +               snp_disable_vmpck(snp_dev);
> +               return rc;
> +       }
> +
> +       /* Increment to new message sequence after payload decryption was successful. */
> +       snp_inc_msg_seqno(snp_dev);
> +
> +       return 0;
> +}
> +
> +static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
> +{
> +       struct snp_guest_crypto *crypto = snp_dev->crypto;
> +       struct snp_report_req req = {0};
> +       struct snp_report_resp *resp;
> +       int rc, resp_len;
> +
> +       if (!arg->req_data || !arg->resp_data)
> +               return -EINVAL;
> +
> +       /* Copy the request payload from userspace */
> +       if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
> +               return -EFAULT;
> +
> +       /*
> +        * The intermediate response buffer is used while decrypting the
> +        * response payload. Make sure that it has enough space to cover the
> +        * authtag.
> +        */
> +       resp_len = sizeof(resp->data) + crypto->a_len;
> +       resp = kzalloc(resp_len, GFP_KERNEL_ACCOUNT);
> +       if (!resp)
> +               return -ENOMEM;
> +
> +       /* Issue the command to get the attestation report */
> +       rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg->msg_version,
> +                                 SNP_MSG_REPORT_REQ, &req, sizeof(req), resp->data,
> +                                 resp_len, &arg->fw_err);
> +       if (rc)
> +               goto e_free;
> +
> +       /* Copy the response payload to userspace */
> +       if (copy_to_user((void __user *)arg->resp_data, resp, sizeof(*resp)))
> +               rc = -EFAULT;
> +
> +e_free:
> +       kfree(resp);
> +       return rc;
> +}
> +
> +static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
> +{
> +       struct snp_guest_dev *snp_dev = to_snp_dev(file);
> +       void __user *argp = (void __user *)arg;
> +       struct snp_guest_request_ioctl input;
> +       int ret = -ENOTTY;
> +
> +       if (copy_from_user(&input, argp, sizeof(input)))
> +               return -EFAULT;
> +
> +       input.fw_err = 0xff;
> +
> +       /* Message version must be non-zero */
> +       if (!input.msg_version)
> +               return -EINVAL;
> +
> +       mutex_lock(&snp_cmd_mutex);
> +
> +       /* Check if the VMPCK is not empty */
> +       if (is_vmpck_empty(snp_dev)) {
> +               dev_err_ratelimited(snp_dev->dev, "VMPCK is disabled\n");
> +               mutex_unlock(&snp_cmd_mutex);
> +               return -ENOTTY;
> +       }
> +
> +       switch (ioctl) {
> +       case SNP_GET_REPORT:
> +               ret = get_report(snp_dev, &input);
> +               break;
> +       default:
> +               break;
> +       }
> +
> +       mutex_unlock(&snp_cmd_mutex);
> +
> +       if (input.fw_err && copy_to_user(argp, &input, sizeof(input)))
> +               return -EFAULT;
> +
> +       return ret;
> +}
> +
> +static void free_shared_pages(void *buf, size_t sz)
> +{
> +       unsigned int npages = PAGE_ALIGN(sz) >> PAGE_SHIFT;
> +
> +       if (!buf)
> +               return;
> +
> +       /* If fail to restore the encryption mask then leak it. */
> +       if (WARN_ONCE(set_memory_encrypted((unsigned long)buf, npages),
> +                     "Failed to restore encryption mask (leak it)\n"))
> +               return;
> +
> +       __free_pages(virt_to_page(buf), get_order(sz));
> +}
> +
> +static void *alloc_shared_pages(size_t sz)
> +{
> +       unsigned int npages = PAGE_ALIGN(sz) >> PAGE_SHIFT;
> +       struct page *page;
> +       int ret;
> +
> +       page = alloc_pages(GFP_KERNEL_ACCOUNT, get_order(sz));
> +       if (IS_ERR(page))
> +               return NULL;
> +
> +       ret = set_memory_decrypted((unsigned long)page_address(page), npages);
> +       if (ret) {
> +               pr_err("SEV-SNP: failed to mark page shared, ret=%d\n", ret);
> +               __free_pages(page, get_order(sz));
> +               return NULL;
> +       }
> +
> +       return page_address(page);
> +}
> +
> +static const struct file_operations snp_guest_fops = {
> +       .owner  = THIS_MODULE,
> +       .unlocked_ioctl = snp_guest_ioctl,
> +};
> +
> +static u8 *get_vmpck(int id, struct snp_secrets_page_layout *layout, u32 **seqno)
> +{
> +       u8 *key = NULL;
> +
> +       switch (id) {
> +       case 0:
> +               *seqno = &layout->os_area.msg_seqno_0;
> +               key = layout->vmpck0;
> +               break;
> +       case 1:
> +               *seqno = &layout->os_area.msg_seqno_1;
> +               key = layout->vmpck1;
> +               break;
> +       case 2:
> +               *seqno = &layout->os_area.msg_seqno_2;
> +               key = layout->vmpck2;
> +               break;
> +       case 3:
> +               *seqno = &layout->os_area.msg_seqno_3;
> +               key = layout->vmpck3;
> +               break;
> +       default:
> +               break;
> +       }
> +
> +       return key;
> +}
> +
> +static int __init snp_guest_probe(struct platform_device *pdev)
> +{
> +       struct snp_secrets_page_layout *layout;
> +       struct snp_guest_platform_data *data;
> +       struct device *dev = &pdev->dev;
> +       struct snp_guest_dev *snp_dev;
> +       struct miscdevice *misc;
> +       int ret;
> +
> +       if (!dev->platform_data)
> +               return -ENODEV;
> +
> +       data = (struct snp_guest_platform_data *)dev->platform_data;
> +       layout = (__force void *)ioremap_encrypted(data->secrets_gpa, PAGE_SIZE);
> +       if (!layout)
> +               return -ENODEV;
> +
> +       ret = -ENOMEM;
> +       snp_dev = devm_kzalloc(&pdev->dev, sizeof(struct snp_guest_dev), GFP_KERNEL);
> +       if (!snp_dev)
> +               goto e_fail;
> +
> +       ret = -EINVAL;
> +       snp_dev->vmpck = get_vmpck(vmpck_id, layout, &snp_dev->os_area_msg_seqno);
> +       if (!snp_dev->vmpck) {
> +               dev_err(dev, "invalid vmpck id %d\n", vmpck_id);
> +               goto e_fail;
> +       }
> +
> +       /* Verify that VMPCK is not zero. */
> +       if (is_vmpck_empty(snp_dev)) {
> +               dev_err(dev, "vmpck id %d is null\n", vmpck_id);
> +               goto e_fail;
> +       }
> +
> +       platform_set_drvdata(pdev, snp_dev);
> +       snp_dev->dev = dev;
> +       snp_dev->layout = layout;
> +
> +       /* Allocate the shared page used for the request and response message. */
> +       snp_dev->request = alloc_shared_pages(sizeof(struct snp_guest_msg));
> +       if (!snp_dev->request)
> +               goto e_fail;
> +
> +       snp_dev->response = alloc_shared_pages(sizeof(struct snp_guest_msg));
> +       if (!snp_dev->response)
> +               goto e_fail;
> +
> +       ret = -EIO;
> +       snp_dev->crypto = init_crypto(snp_dev, snp_dev->vmpck, VMPCK_KEY_LEN);
> +       if (!snp_dev->crypto)
> +               goto e_fail;
> +
> +       misc = &snp_dev->misc;
> +       misc->minor = MISC_DYNAMIC_MINOR;
> +       misc->name = DEVICE_NAME;
> +       misc->fops = &snp_guest_fops;
> +
> +       /* initial the input address for guest request */
> +       snp_dev->input.req_gpa = __pa(snp_dev->request);
> +       snp_dev->input.resp_gpa = __pa(snp_dev->response);
> +
> +       ret =  misc_register(misc);
> +       if (ret)
> +               goto e_fail;
> +
> +       dev_info(dev, "Initialized SEV-SNP guest driver (using vmpck_id %d)\n", vmpck_id);
> +       return 0;
> +
> +e_fail:
> +       iounmap(layout);
> +       free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg));
> +       free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg));
> +
> +       return ret;
> +}
> +
> +static int __exit snp_guest_remove(struct platform_device *pdev)
> +{
> +       struct snp_guest_dev *snp_dev = platform_get_drvdata(pdev);
> +
> +       free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg));
> +       free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg));
> +       deinit_crypto(snp_dev->crypto);
> +       misc_deregister(&snp_dev->misc);
> +
> +       return 0;
> +}
> +
> +static struct platform_driver snp_guest_driver = {
> +       .remove         = __exit_p(snp_guest_remove),
> +       .driver         = {
> +               .name = "snp-guest",
> +       },
> +};
> +
> +module_platform_driver_probe(snp_guest_driver, snp_guest_probe);
> +
> +MODULE_AUTHOR("Brijesh Singh <brijesh.singh@amd.com>");
> +MODULE_LICENSE("GPL");
> +MODULE_VERSION("1.0.0");
> +MODULE_DESCRIPTION("AMD SNP Guest Driver");
> diff --git a/drivers/virt/coco/sevguest/sevguest.h b/drivers/virt/coco/sevguest/sevguest.h
> new file mode 100644
> index 000000000000..cfa76cf8a21a
> --- /dev/null
> +++ b/drivers/virt/coco/sevguest/sevguest.h
> @@ -0,0 +1,98 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2021 Advanced Micro Devices, Inc.
> + *
> + * Author: Brijesh Singh <brijesh.singh@amd.com>
> + *
> + * SEV-SNP API spec is available at https://developer.amd.com/sev
> + */
> +
> +#ifndef __LINUX_SEVGUEST_H_
> +#define __LINUX_SEVGUEST_H_
> +
> +#include <linux/types.h>
> +
> +#define MAX_AUTHTAG_LEN                32
> +
> +/* See SNP spec SNP_GUEST_REQUEST section for the structure */
> +enum msg_type {
> +       SNP_MSG_TYPE_INVALID = 0,
> +       SNP_MSG_CPUID_REQ,
> +       SNP_MSG_CPUID_RSP,
> +       SNP_MSG_KEY_REQ,
> +       SNP_MSG_KEY_RSP,
> +       SNP_MSG_REPORT_REQ,
> +       SNP_MSG_REPORT_RSP,
> +       SNP_MSG_EXPORT_REQ,
> +       SNP_MSG_EXPORT_RSP,
> +       SNP_MSG_IMPORT_REQ,
> +       SNP_MSG_IMPORT_RSP,
> +       SNP_MSG_ABSORB_REQ,
> +       SNP_MSG_ABSORB_RSP,
> +       SNP_MSG_VMRK_REQ,
> +       SNP_MSG_VMRK_RSP,
> +
> +       SNP_MSG_TYPE_MAX
> +};
> +
> +enum aead_algo {
> +       SNP_AEAD_INVALID,
> +       SNP_AEAD_AES_256_GCM,
> +};
> +
> +struct snp_guest_msg_hdr {
> +       u8 authtag[MAX_AUTHTAG_LEN];
> +       u64 msg_seqno;
> +       u8 rsvd1[8];
> +       u8 algo;
> +       u8 hdr_version;
> +       u16 hdr_sz;
> +       u8 msg_type;
> +       u8 msg_version;
> +       u16 msg_sz;
> +       u32 rsvd2;
> +       u8 msg_vmpck;
> +       u8 rsvd3[35];
> +} __packed;
> +
> +struct snp_guest_msg {
> +       struct snp_guest_msg_hdr hdr;
> +       u8 payload[4000];
> +} __packed;
> +
> +/*
> + * The secrets page contains 96-bytes of reserved field that can be used by
> + * the guest OS. The guest OS uses the area to save the message sequence
> + * number for each VMPCK.
> + *
> + * See the GHCB spec section Secret page layout for the format for this area.
> + */
> +struct secrets_os_area {
> +       u32 msg_seqno_0;
> +       u32 msg_seqno_1;
> +       u32 msg_seqno_2;
> +       u32 msg_seqno_3;
> +       u64 ap_jump_table_pa;
> +       u8 rsvd[40];
> +       u8 guest_usage[32];
> +} __packed;
> +
> +#define VMPCK_KEY_LEN          32
> +
> +/* See the SNP spec version 0.9 for secrets page format */
> +struct snp_secrets_page_layout {
> +       u32 version;
> +       u32 imien       : 1,
> +           rsvd1       : 31;
> +       u32 fms;
> +       u32 rsvd2;
> +       u8 gosvw[16];
> +       u8 vmpck0[VMPCK_KEY_LEN];
> +       u8 vmpck1[VMPCK_KEY_LEN];
> +       u8 vmpck2[VMPCK_KEY_LEN];
> +       u8 vmpck3[VMPCK_KEY_LEN];
> +       struct secrets_os_area os_area;
> +       u8 rsvd3[3840];
> +} __packed;
> +
> +#endif /* __LINUX_SNP_GUEST_H__ */
> diff --git a/include/uapi/linux/sev-guest.h b/include/uapi/linux/sev-guest.h
> new file mode 100644
> index 000000000000..081d314a6279
> --- /dev/null
> +++ b/include/uapi/linux/sev-guest.h
> @@ -0,0 +1,50 @@
> +/* SPDX-License-Identifier: GPL-2.0-only WITH Linux-syscall-note */
> +/*
> + * Userspace interface for AMD SEV and SEV-SNP guest driver.
> + *
> + * Copyright (C) 2021 Advanced Micro Devices, Inc.
> + *
> + * Author: Brijesh Singh <brijesh.singh@amd.com>
> + *
> + * SEV API specification is available at: https://developer.amd.com/sev/
> + */
> +
> +#ifndef __UAPI_LINUX_SEV_GUEST_H_
> +#define __UAPI_LINUX_SEV_GUEST_H_
> +
> +#include <linux/types.h>
> +
> +struct snp_report_req {
> +       /* user data that should be included in the report */
> +       __u8 user_data[64];
> +
> +       /* The vmpl level to be included in the report */
> +       __u32 vmpl;
> +
> +       /* Must be zero filled */
> +       __u8 rsvd[28];
> +};
> +
> +struct snp_report_resp {
> +       /* response data, see SEV-SNP spec for the format */
> +       __u8 data[4000];
> +};
> +
> +struct snp_guest_request_ioctl {
> +       /* message version number (must be non-zero) */
> +       __u8 msg_version;
> +
> +       /* Request and response structure address */
> +       __u64 req_data;
> +       __u64 resp_data;
> +
> +       /* firmware error code on failure (see psp-sev.h) */
> +       __u64 fw_err;
> +};
> +
> +#define SNP_GUEST_REQ_IOC_TYPE 'S'
> +
> +/* Get SNP attestation report */
> +#define SNP_GET_REPORT _IOWR(SNP_GUEST_REQ_IOC_TYPE, 0x0, struct snp_guest_request_ioctl)
> +
> +#endif /* __UAPI_LINUX_SEV_GUEST_H_ */
> --
> 2.25.1
>

On Fri, Jan 28, 2022 at 11:18:02AM -0600, Brijesh Singh wrote:
> SEV-SNP specification provides the guest a mechanism to communicate with
 ^
 The

> the PSP without risk from a malicious hypervisor who wishes to read, alter,
> drop or replay the messages sent. The driver uses snp_issue_guest_request()
> to issue GHCB SNP_GUEST_REQUEST or SNP_EXT_GUEST_REQUEST NAE events to
> submit the request to PSP.
> 
> The PSP requires that all communication should be encrypted using key
> specified through the platform_data.
> 
> The userspace can use SNP_GET_REPORT ioctl() to query the guest

s/The u/U/

> attestation report.
> 
> See SEV-SNP spec section Guest Messages for more details.
> 
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
>  Documentation/virt/coco/sevguest.rst  |  81 ++++
>  drivers/virt/Kconfig                  |   3 +
>  drivers/virt/Makefile                 |   1 +
>  drivers/virt/coco/sevguest/Kconfig    |  12 +
>  drivers/virt/coco/sevguest/Makefile   |   2 +
>  drivers/virt/coco/sevguest/sevguest.c | 605 ++++++++++++++++++++++++++
>  drivers/virt/coco/sevguest/sevguest.h |  98 +++++
>  include/uapi/linux/sev-guest.h        |  50 +++
>  8 files changed, 852 insertions(+)
>  create mode 100644 Documentation/virt/coco/sevguest.rst
>  create mode 100644 drivers/virt/coco/sevguest/Kconfig
>  create mode 100644 drivers/virt/coco/sevguest/Makefile
>  create mode 100644 drivers/virt/coco/sevguest/sevguest.c
>  create mode 100644 drivers/virt/coco/sevguest/sevguest.h
>  create mode 100644 include/uapi/linux/sev-guest.h
> 
> diff --git a/Documentation/virt/coco/sevguest.rst b/Documentation/virt/coco/sevguest.rst
> new file mode 100644
> index 000000000000..47ef3b0821d5
> --- /dev/null
> +++ b/Documentation/virt/coco/sevguest.rst

Adding documentation is all fine and good but you need to link that file
into the TOC somewhere so that it is visible when the documentation gets
generated... I guess something like this:

diff --git a/Documentation/virt/index.rst b/Documentation/virt/index.rst
index edea7fea95a8..40ad0d20032e 100644
--- a/Documentation/virt/index.rst
+++ b/Documentation/virt/index.rst
@@ -13,6 +13,7 @@ Linux Virtualization Support
    guest-halt-polling
    ne_overview
    acrn/index
+   coco/sevguest
 
 .. only:: html and subproject
 


And once you do, do "make htmldocs" to see whether it complains about
some formatting issues or other errors etc.

/me goes and does it...

Ah, here we go:

Documentation/virt/coco/sevguest.rst:48: WARNING: Inline emphasis start-string without end-string.
Documentation/virt/coco/sevguest.rst:51: WARNING: Inline emphasis start-string without end-string.
Documentation/virt/coco/sevguest.rst:55: WARNING: Inline emphasis start-string without end-string.
Documentation/virt/coco/sevguest.rst:57: WARNING: Definition list ends without a blank line; unexpected unindent.

There's something it doesn't like about the struct. Yeah, when I look at
the html output, it is all weird and not monospaced...

> @@ -0,0 +1,81 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +===================================================================
> +The Definitive SEV Guest API Documentation
> +===================================================================
> +
> +1. General description
> +======================
> +
> +The SEV API is a set of ioctls that are used by the guest or hypervisor
> +to get or set certain aspect of the SEV virtual machine. The ioctls belong
		^
		a

> +to the following classes:
> +
> + - Hypervisor ioctls: These query and set global attributes which affect the
> +   whole SEV firmware.  These ioctl are used by platform provision tools.

"provisioning" maybe?

> +
> + - Guest ioctls: These query and set attributes of the SEV virtual machine.
> +
> +2. API description
> +==================
> +
> +This section describes ioctls that can be used to query or set SEV guests.
							      ^^^^^^^^^^^^^^^

That sounds weird.

> +For each ioctl, the following information is provided along with a
> +description:
> +
> +  Technology:
> +      which SEV technology provides this ioctl. sev, sev-es, sev-snp or all.
						   ^^^^^^^^^^^^^^^^^^^^

Marketing is going to scold you - those need to be in all caps. :-P

> +
> +  Type:
> +      hypervisor or guest. The ioctl can be used inside the guest or the
> +      hypervisor.
> +
> +  Parameters:
> +      what parameters are accepted by the ioctl.
> +
> +  Returns:
> +      the return value.  General error numbers (ENOMEM, EINVAL)

Those are negative: -ENOMEM, -EINVAL

> +      are not detailed, but errors with specific meanings are.
> +
> +The guest ioctl should be issued on a file descriptor of the /dev/sev-guest device.
> +The ioctl accepts struct snp_user_guest_request. The input and output structure is
> +specified through the req_data and resp_data field respectively. If the ioctl fails
> +to execute due to a firmware error, then fw_err code will be set otherwise the
> +fw_err will be set to 0xff.

fw_err is u64. What does 0xff mean? Everything above the least
significant byte is reserved 0?

> diff --git a/drivers/virt/coco/sevguest/Kconfig b/drivers/virt/coco/sevguest/Kconfig
> new file mode 100644
> index 000000000000..07ab9ec6471c
> --- /dev/null
> +++ b/drivers/virt/coco/sevguest/Kconfig
> @@ -0,0 +1,12 @@
> +config SEV_GUEST
> +	tristate "AMD SEV Guest driver"
> +	default y

Definitely not. We don't enable drivers by default unless they're
ubiquitous.

> +	depends on AMD_MEM_ENCRYPT && CRYPTO_AEAD2
> +	help
> +	  SEV-SNP firmware provides the guest a mechanism to communicate with
> +	  the PSP without risk from a malicious hypervisor who wishes to read,
> +	  alter, drop or replay the messages sent. The driver provides
> +	  userspace interface to communicate with the PSP to request the
> +	  attestation report and more.
> +
> +	  If you choose 'M' here, this module will be called sevguest.

...

> +static bool is_vmpck_empty(struct snp_guest_dev *snp_dev)
> +{
> +	char zero_key[VMPCK_KEY_LEN] = {0};
> +
> +	if (snp_dev->vmpck)
> +		return memcmp(snp_dev->vmpck, zero_key, VMPCK_KEY_LEN) == 0;

		return !memcmp(...);
> +
> +	return true;
> +}
> +
> +static void snp_disable_vmpck(struct snp_guest_dev *snp_dev)
> +{
> +	memzero_explicit(snp_dev->vmpck, VMPCK_KEY_LEN);
> +	snp_dev->vmpck = NULL;
> +}
> +
> +static inline u64 __snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
> +{
> +	u64 count;
> +
> +	lockdep_assert_held(&snp_cmd_mutex);
> +
> +	/* Read the current message sequence counter from secrets pages */
> +	count = *snp_dev->os_area_msg_seqno;
> +
> +	return count + 1;
> +}
> +
> +/* Return a non-zero on success */
> +static u64 snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
> +{
> +	u64 count = __snp_get_msg_seqno(snp_dev);
> +
> +	/*
> +	 * The message sequence counter for the SNP guest request is a  64-bit
> +	 * value but the version 2 of GHCB specification defines a 32-bit storage
> +	 * for it. If the counter exceeds the 32-bit value then return zero.
> +	 * The caller should check the return value, but if the caller happens to
> +	 * not check the value and use it, then the firmware treats zero as an
> +	 * invalid number and will fail the  message request.
> +	 */
> +	if (count >= UINT_MAX) {
> +		pr_err_ratelimited("SNP guest request message sequence counter overflow\n");

How does error message help the user? Is she supposed to reboot the
machine or so?

Because it sounds to me like if this goes over 32-bit, this driver stops
working. So what resets those sequence numbers?

> +		return 0;
> +	}
> +
> +	return count;
> +}
> +
> +static void snp_inc_msg_seqno(struct snp_guest_dev *snp_dev)
> +{
> +	/*
> +	 * The counter is also incremented by the PSP, so increment it by 2
> +	 * and save in secrets page.
> +	 */
> +	*snp_dev->os_area_msg_seqno += 2;
> +}
> +
> +static inline struct snp_guest_dev *to_snp_dev(struct file *file)
> +{
> +	struct miscdevice *dev = file->private_data;
> +
> +	return container_of(dev, struct snp_guest_dev, misc);
> +}
> +
> +static struct snp_guest_crypto *init_crypto(struct snp_guest_dev *snp_dev, u8 *key, size_t keylen)
> +{
> +	struct snp_guest_crypto *crypto;
> +
> +	crypto = kzalloc(sizeof(*crypto), GFP_KERNEL_ACCOUNT);
> +	if (!crypto)
> +		return NULL;
> +
> +	crypto->tfm = crypto_alloc_aead("gcm(aes)", 0, 0);
> +	if (IS_ERR(crypto->tfm))
> +		goto e_free;
> +
> +	if (crypto_aead_setkey(crypto->tfm, key, keylen))
> +		goto e_free_crypto;
> +
> +	crypto->iv_len = crypto_aead_ivsize(crypto->tfm);
> +	if (crypto->iv_len < 12) {
> +		dev_err(snp_dev->dev, "IV length is less than 12.\n");

And? < 12 is bad? Make that error message more user-friendly pls.

> +		goto e_free_crypto;
> +	}
> +
> +	crypto->iv = kmalloc(crypto->iv_len, GFP_KERNEL_ACCOUNT);
> +	if (!crypto->iv)
> +		goto e_free_crypto;
> +
> +	if (crypto_aead_authsize(crypto->tfm) > MAX_AUTHTAG_LEN) {
> +		if (crypto_aead_setauthsize(crypto->tfm, MAX_AUTHTAG_LEN)) {
> +			dev_err(snp_dev->dev, "failed to set authsize to %d\n", MAX_AUTHTAG_LEN);
> +			goto e_free_crypto;
> +		}
> +	}
> +
> +	crypto->a_len = crypto_aead_authsize(crypto->tfm);
> +	crypto->authtag = kmalloc(crypto->a_len, GFP_KERNEL_ACCOUNT);
> +	if (!crypto->authtag)
> +		goto e_free_crypto;
> +
> +	return crypto;
> +
> +e_free_crypto:
> +	crypto_free_aead(crypto->tfm);
> +e_free:
> +	kfree(crypto->iv);
> +	kfree(crypto->authtag);
> +	kfree(crypto);

The order of those free calls needs to be the opposite of the kmallocs
above.

> +
> +	return NULL;
> +}

...

> +static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, int msg_ver,
> +				u8 type, void *req_buf, size_t req_sz, void *resp_buf,
> +				u32 resp_sz, __u64 *fw_err)
> +{
> +	unsigned long err;
> +	u64 seqno;
> +	int rc;
> +
> +	/* Get message sequence and verify that its a non-zero */
> +	seqno = snp_get_msg_seqno(snp_dev);
> +	if (!seqno)
> +		return -EIO;
> +
> +	memset(snp_dev->response, 0, sizeof(*snp_dev->response));

				     sizeof(struct snp_guest_msg)

> +
> +	/* Encrypt the userspace provided payload */
> +	rc = enc_payload(snp_dev, seqno, msg_ver, type, req_buf, req_sz);
> +	if (rc)
> +		return rc;
> +
> +	/* Call firmware to process the request */
> +	rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);
> +	if (fw_err)
> +		*fw_err = err;
> +
> +	if (rc)
> +		return rc;
> +
> +	rc = verify_and_dec_payload(snp_dev, resp_buf, resp_sz);
> +	if (rc) {
> +		/*
> +		 * The verify_and_dec_payload() will fail only if the hypervisor is
> +		 * actively modifying the message header or corrupting the encrypted payload.
> +		 * This hints that hypervisor is acting in a bad faith. Disable the VMPCK so that
> +		 * the key cannot be used for any communication. The key is disabled to ensure
> +		 * that AES-GCM does not use the same IV while encrypting the request payload.
> +		 */

Put that comment over the function call.

> +		dev_alert(snp_dev->dev,
> +			  "Detected unexpected decode failure, disabling the vmpck_id %d\n",
> +			  vmpck_id);
> +		snp_disable_vmpck(snp_dev);
> +		return rc;
> +	}
> +
> +	/* Increment to new message sequence after payload decryption was successful. */
> +	snp_inc_msg_seqno(snp_dev);
> +
> +	return 0;
> +}
> +
> +static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
> +{
> +	struct snp_guest_crypto *crypto = snp_dev->crypto;
> +	struct snp_report_req req = {0};
> +	struct snp_report_resp *resp;
> +	int rc, resp_len;

	lockdep_assert_held(&snp_cmd_mutex);

> +	if (!arg->req_data || !arg->resp_data)
> +		return -EINVAL;
> +
> +	/* Copy the request payload from userspace */
> +	if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
> +		return -EFAULT;
> +
> +	/*
> +	 * The intermediate response buffer is used while decrypting the
> +	 * response payload. Make sure that it has enough space to cover the
> +	 * authtag.
> +	 */
> +	resp_len = sizeof(resp->data) + crypto->a_len;
> +	resp = kzalloc(resp_len, GFP_KERNEL_ACCOUNT);
> +	if (!resp)
> +		return -ENOMEM;
> +
> +	/* Issue the command to get the attestation report */
> +	rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg->msg_version,
> +				  SNP_MSG_REPORT_REQ, &req, sizeof(req), resp->data,
> +				  resp_len, &arg->fw_err);
> +	if (rc)
> +		goto e_free;
> +
> +	/* Copy the response payload to userspace */
> +	if (copy_to_user((void __user *)arg->resp_data, resp, sizeof(*resp)))
> +		rc = -EFAULT;
> +
> +e_free:
> +	kfree(resp);
> +	return rc;
> +}
> +
> +static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
> +{
> +	struct snp_guest_dev *snp_dev = to_snp_dev(file);
> +	void __user *argp = (void __user *)arg;
> +	struct snp_guest_request_ioctl input;
> +	int ret = -ENOTTY;
> +
> +	if (copy_from_user(&input, argp, sizeof(input)))
> +		return -EFAULT;
> +
> +	input.fw_err = 0xff;
> +
> +	/* Message version must be non-zero */
> +	if (!input.msg_version)
> +		return -EINVAL;
> +
> +	mutex_lock(&snp_cmd_mutex);

That mutex probably is to be held while issuing SNP commands but then
you hold it here already for...

> +
> +	/* Check if the VMPCK is not empty */
> +	if (is_vmpck_empty(snp_dev)) {

... this here which is not really a SNP command issuing.

Should that mutex be grabbed only around handle_guest_request() above or
is it supposed to protect more stuff?

> +		dev_err_ratelimited(snp_dev->dev, "VMPCK is disabled\n");
> +		mutex_unlock(&snp_cmd_mutex);
> +		return -ENOTTY;
> +	}
> +
> +	switch (ioctl) {
> +	case SNP_GET_REPORT:
> +		ret = get_report(snp_dev, &input);
> +		break;
> +	default:
> +		break;
> +	}
> +
> +	mutex_unlock(&snp_cmd_mutex);
> +
> +	if (input.fw_err && copy_to_user(argp, &input, sizeof(input)))
> +		return -EFAULT;
> +
> +	return ret;
> +}
> +
> +static void free_shared_pages(void *buf, size_t sz)
> +{
> +	unsigned int npages = PAGE_ALIGN(sz) >> PAGE_SHIFT;
> +
> +	if (!buf)
> +		return;
> +
> +	/* If fail to restore the encryption mask then leak it. */

Useless comment - the error message says the same.

> +	if (WARN_ONCE(set_memory_encrypted((unsigned long)buf, npages),
> +		      "Failed to restore encryption mask (leak it)\n"))
> +		return;
> +
> +	__free_pages(virt_to_page(buf), get_order(sz));
> +}
> +
> +static void *alloc_shared_pages(size_t sz)
> +{
> +	unsigned int npages = PAGE_ALIGN(sz) >> PAGE_SHIFT;
> +	struct page *page;
> +	int ret;
> +
> +	page = alloc_pages(GFP_KERNEL_ACCOUNT, get_order(sz));
> +	if (IS_ERR(page))
> +		return NULL;
> +
> +	ret = set_memory_decrypted((unsigned long)page_address(page), npages);
> +	if (ret) {
> +		pr_err("SEV-SNP: failed to mark page shared, ret=%d\n", ret);

Use pr_fmt, grep the tree for an example how and drop "SEV-SNP:" - that
prefix should be "sevguest:".

> +		__free_pages(page, get_order(sz));
> +		return NULL;
> +	}
> +
> +	return page_address(page);
> +}

...

> +static int __init snp_guest_probe(struct platform_device *pdev)
> +{
> +	struct snp_secrets_page_layout *layout;
> +	struct snp_guest_platform_data *data;
> +	struct device *dev = &pdev->dev;
> +	struct snp_guest_dev *snp_dev;
> +	struct miscdevice *misc;
> +	int ret;
> +
> +	if (!dev->platform_data)
> +		return -ENODEV;
> +
> +	data = (struct snp_guest_platform_data *)dev->platform_data;
> +	layout = (__force void *)ioremap_encrypted(data->secrets_gpa, PAGE_SIZE);
> +	if (!layout)
> +		return -ENODEV;
> +
> +	ret = -ENOMEM;
> +	snp_dev = devm_kzalloc(&pdev->dev, sizeof(struct snp_guest_dev), GFP_KERNEL);
> +	if (!snp_dev)
> +		goto e_fail;
> +
> +	ret = -EINVAL;
> +	snp_dev->vmpck = get_vmpck(vmpck_id, layout, &snp_dev->os_area_msg_seqno);
> +	if (!snp_dev->vmpck) {
> +		dev_err(dev, "invalid vmpck id %d\n", vmpck_id);
> +		goto e_fail;
> +	}
> +
> +	/* Verify that VMPCK is not zero. */
> +	if (is_vmpck_empty(snp_dev)) {
> +		dev_err(dev, "vmpck id %d is null\n", vmpck_id);
> +		goto e_fail;
> +	}
> +
> +	platform_set_drvdata(pdev, snp_dev);
> +	snp_dev->dev = dev;
> +	snp_dev->layout = layout;
> +
> +	/* Allocate the shared page used for the request and response message. */
> +	snp_dev->request = alloc_shared_pages(sizeof(struct snp_guest_msg));
> +	if (!snp_dev->request)
> +		goto e_fail;
> +
> +	snp_dev->response = alloc_shared_pages(sizeof(struct snp_guest_msg));
> +	if (!snp_dev->response)
> +		goto e_fail;
> +
> +	ret = -EIO;
> +	snp_dev->crypto = init_crypto(snp_dev, snp_dev->vmpck, VMPCK_KEY_LEN);
> +	if (!snp_dev->crypto)
> +		goto e_fail;
> +
> +	misc = &snp_dev->misc;
> +	misc->minor = MISC_DYNAMIC_MINOR;
> +	misc->name = DEVICE_NAME;
> +	misc->fops = &snp_guest_fops;
> +
> +	/* initial the input address for guest request */
> +	snp_dev->input.req_gpa = __pa(snp_dev->request);
> +	snp_dev->input.resp_gpa = __pa(snp_dev->response);
> +
> +	ret =  misc_register(misc);
> +	if (ret)
> +		goto e_fail;
> +
> +	dev_info(dev, "Initialized SEV-SNP guest driver (using vmpck_id %d)\n", vmpck_id);
> +	return 0;
> +
> +e_fail:
> +	iounmap(layout);
> +	free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg));
> +	free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg));

The freeing needs to happen in the opposite order of the allocations.
Audit all gotos.

> +
> +	return ret;
> +}
> +
> +static int __exit snp_guest_remove(struct platform_device *pdev)
> +{
> +	struct snp_guest_dev *snp_dev = platform_get_drvdata(pdev);
> +
> +	free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg));
> +	free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg));
> +	deinit_crypto(snp_dev->crypto);
> +	misc_deregister(&snp_dev->misc);
> +
> +	return 0;
> +}
> +
> +static struct platform_driver snp_guest_driver = {
> +	.remove		= __exit_p(snp_guest_remove),
> +	.driver		= {
> +		.name = "snp-guest",
> +	},
> +};
> +
> +module_platform_driver_probe(snp_guest_driver, snp_guest_probe);
> +
> +MODULE_AUTHOR("Brijesh Singh <brijesh.singh@amd.com>");
> +MODULE_LICENSE("GPL");
> +MODULE_VERSION("1.0.0");
> +MODULE_DESCRIPTION("AMD SNP Guest Driver");
> diff --git a/drivers/virt/coco/sevguest/sevguest.h b/drivers/virt/coco/sevguest/sevguest.h
> new file mode 100644
> index 000000000000..cfa76cf8a21a
> --- /dev/null
> +++ b/drivers/virt/coco/sevguest/sevguest.h
> @@ -0,0 +1,98 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2021 Advanced Micro Devices, Inc.
> + *
> + * Author: Brijesh Singh <brijesh.singh@amd.com>
> + *
> + * SEV-SNP API spec is available at https://developer.amd.com/sev
> + */
> +
> +#ifndef __LINUX_SEVGUEST_H_

I guess VIRT_SEVGUEST_H is better fitting.

> +#define __LINUX_SEVGUEST_H_

...

On 2/6/22 4:39 PM, Borislav Petkov wrote:

> And once you do, do "make htmldocs" to see whether it complains about
> some formatting issues or other errors etc.
> 
> /me goes and does it...
> 
> Ah, here we go:
> 
> Documentation/virt/coco/sevguest.rst:48: WARNING: Inline emphasis start-string without end-string.
> Documentation/virt/coco/sevguest.rst:51: WARNING: Inline emphasis start-string without end-string.
> Documentation/virt/coco/sevguest.rst:55: WARNING: Inline emphasis start-string without end-string.
> Documentation/virt/coco/sevguest.rst:57: WARNING: Definition list ends without a blank line; unexpected unindent.
> 
> There's something it doesn't like about the struct. Yeah, when I look at
> the html output, it is all weird and not monospaced...

I will fix those in next rev.


>> +
>> +The guest ioctl should be issued on a file descriptor of the /dev/sev-guest device.
>> +The ioctl accepts struct snp_user_guest_request. The input and output structure is
>> +specified through the req_data and resp_data field respectively. If the ioctl fails
>> +to execute due to a firmware error, then fw_err code will be set otherwise the
>> +fw_err will be set to 0xff.
> 
> fw_err is u64. What does 0xff mean? Everything above the least
> significant byte is reserved 0?
> 

Yep, I will explicitly say that it should be set to 0x00000000000000FF.


>> diff --git a/drivers/virt/coco/sevguest/Kconfig b/drivers/virt/coco/sevguest/Kconfig
>> new file mode 100644
>> index 000000000000..07ab9ec6471c
>> --- /dev/null
>> +++ b/drivers/virt/coco/sevguest/Kconfig
>> @@ -0,0 +1,12 @@
>> +config SEV_GUEST
>> +	tristate "AMD SEV Guest driver"
>> +	default y
> 
> Definitely not. We don't enable drivers by default unless they're
> ubiquitous.
> 

Randy asked me similar question on v7, and here is my response to it.

https://lore.kernel.org/linux-mm/e6b412e4-f38e-d212-f52a-e7bdc9a26eff@infradead.org/

Let me know if you still think that we should make it 'n'. I am not dead 
against it but I have feeling that once distro's starts building SNP 
aware guest kernel, then we may get asked to enable it by default so 
that attestation report can be obtained by the initial ramdisk.



>> +	 */
>> +	if (count >= UINT_MAX) {
>> +		pr_err_ratelimited("SNP guest request message sequence counter overflow\n");
> 
> How does error message help the user? Is she supposed to reboot the
> machine or so?
> 
> Because it sounds to me like if this goes over 32-bit, this driver stops
> working. So what resets those sequence numbers?

After this condition is met, a guest will no longer get the attestation 
report. It's up to the userspace to reboot the guest or continue without 
attestation.

The only thing that will reset the counter is re-launching the guest to 
go through the entire PSP initialization sequence once again.


>> +
>> +	crypto->iv_len = crypto_aead_ivsize(crypto->tfm);
>> +	if (crypto->iv_len < 12) {
>> +		dev_err(snp_dev->dev, "IV length is less than 12.\n");
> 
> And? < 12 is bad? Make that error message more user-friendly pls.
> 
Okay.


> 
> The order of those free calls needs to be the opposite of the kmallocs
> above.
> 
Okay


>> +
>> +	/* Message version must be non-zero */
>> +	if (!input.msg_version)
>> +		return -EINVAL;
>> +
>> +	mutex_lock(&snp_cmd_mutex);
> 
> That mutex probably is to be held while issuing SNP commands but then
> you hold it here already for...
> 
>> +
>> +	/* Check if the VMPCK is not empty */
>> +	if (is_vmpck_empty(snp_dev)) {
> 
> ... this here which is not really a SNP command issuing.
> 
> Should that mutex be grabbed only around handle_guest_request() above or
> is it supposed to protect more stuff?


Yep, it need to protect more stuff.

We allocate a shared buffers (request, response, cert-chain) that gets 
populated before issuing the command, and then we copy the result from 
reponse shared to callers buffer after the command completes. So, we 
also want to ensure that the shared buffer is not touched before the 
previous ioctl is finished.


-Brijesh

On Mon, Feb 07, 2022 at 08:41:47AM -0600, Brijesh Singh wrote:
> Randy asked me similar question on v7, and here is my response to it.
> 
> https://lore.kernel.org/linux-mm/e6b412e4-f38e-d212-f52a-e7bdc9a26eff@infradead.org/
> 
> Let me know if you still think that we should make it 'n'. I am not dead
> against it but I have feeling that once distro's starts building SNP aware
> guest kernel, then we may get asked to enable it by default so that
> attestation report can be obtained by the initial ramdisk.

Well, let's see:

$ make oldconfig
...

#
# No change to .config
#
$

So it didn't even ask me. Because

# CONFIG_VIRT_DRIVERS is not set

so what's the point of this "default y"?

If the distros are your worry, then you probably will have to ask
them to do so explicitly anyway because at least we edit our configs
ourselves and decide what to enable or what not.

> After this condition is met, a guest will no longer get the attestation
> report. It's up to the userspace to reboot the guest or continue without
> attestation.
> 
> The only thing that will reset the counter is re-launching the guest to go
> through the entire PSP initialization sequence once again.

Well, but you need to explain that somewhere to the guest owners.
I guess either here in that error message or in some higher-level
glue which will do the attestation. Just saying that some counter has
overflown is not very user-friendly, I'd say.

> Yep, it need to protect more stuff.
> 
> We allocate a shared buffers (request, response, cert-chain) that gets
> populated before issuing the command, and then we copy the result from
> reponse shared to callers buffer after the command completes. So, we also
> want to ensure that the shared buffer is not touched before the previous
> ioctl is finished.

So you need to rename that mutex and slap a comment above it what it
protects.

Thx.