[RFC,3/3] virt: Add sev_secret module to expose confidential computing secrets

diff --git a/drivers/virt/Kconfig b/drivers/virt/Kconfig
index 8061e8ef449f..c222cc625891 100644
--- a/drivers/virt/Kconfig
+++ b/drivers/virt/Kconfig
@@ -36,4 +36,6 @@  source "drivers/virt/vboxguest/Kconfig"
 source "drivers/virt/nitro_enclaves/Kconfig"
 
 source "drivers/virt/acrn/Kconfig"
+
+source "drivers/virt/sev_secret/Kconfig"
 endif
diff --git a/drivers/virt/Makefile b/drivers/virt/Makefile
index 3e272ea60cd9..0765e5418d1d 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-y				+= sev_secret/
diff --git a/drivers/virt/sev_secret/Kconfig b/drivers/virt/sev_secret/Kconfig
new file mode 100644
index 000000000000..4505526b8ef1
--- /dev/null
+++ b/drivers/virt/sev_secret/Kconfig
@@ -0,0 +1,11 @@ 
+# SPDX-License-Identifier: GPL-2.0-only
+config AMD_SEV_SECRET_SECURITYFS
+	tristate "AMD SEV secret area securityfs support"
+	depends on EFI
+	select SECURITYFS
+	help
+	  This is a driver for accessing the AMD SEV secret area via
+	  securityfs.
+
+	  To compile this driver as a module, choose M here.
+	  The module will be called sev_secret.
diff --git a/drivers/virt/sev_secret/Makefile b/drivers/virt/sev_secret/Makefile
new file mode 100644
index 000000000000..9671f7bb3941
--- /dev/null
+++ b/drivers/virt/sev_secret/Makefile
@@ -0,0 +1,2 @@ 
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_AMD_SEV_SECRET_SECURITYFS) += sev_secret.o
diff --git a/drivers/virt/sev_secret/sev_secret.c b/drivers/virt/sev_secret/sev_secret.c
new file mode 100644
index 000000000000..9fff62356e74
--- /dev/null
+++ b/drivers/virt/sev_secret/sev_secret.c
@@ -0,0 +1,260 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * sev_secret module
+ *
+ * Copyright (C) 2021 IBM Corporation
+ * Author: Dov Murik <dovmurik@linux.ibm.com>
+ */
+
+#include <linux/seq_file.h>
+#include <linux/fs.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/io.h>
+#include <linux/security.h>
+#include <linux/efi.h>
+
+/**
+ * sev_secret: Allow reading confidential computing secret area via securityfs
+ * interface.
+ *
+ * When the module is loaded (and securityfs is mounted, typically under
+ * /sys/kernel/security), an "sev_secret" directory is created in securityfs.
+ * In it, a file is created for each secret entry.  The name of each such file
+ * is the GUID of the secret entry, and its content is the secret data.
+ */
+
+#define SEV_SECRET_NUM_FILES 64
+
+#define EFI_SEVSECRET_TABLE_HEADER_GUID \
+	EFI_GUID(0x1e74f542, 0x71dd, 0x4d66, 0x96, 0x3e, 0xef, 0x42, 0x87, 0xff, 0x17, 0x3b)
+
+struct sev_secret {
+	struct dentry *fs_dir;
+	struct dentry *fs_files[SEV_SECRET_NUM_FILES];
+	struct linux_efi_confidential_computing_secret_area *secret_area;
+};
+
+/*
+ * Structure of the SEV secret area
+ *
+ * Offset   Length
+ * (bytes)  (bytes)  Usage
+ * -------  -------  -----
+ *       0       16  Secret table header GUID (must be 1e74f542-71dd-4d66-963e-ef4287ff173b)
+ *      16        4  Length of bytes of the entire secret area
+ *
+ *      20       16  First secret entry's GUID
+ *      36        4  First secret entry's length in bytes (= 16 + 4 + x)
+ *      40        x  First secret entry's data
+ *
+ *    40+x       16  Second secret entry's GUID
+ *    56+x        4  Second secret entry's length in bytes (= 16 + 4 + y)
+ *    60+x        y  Second secret entry's data
+ *
+ * (... and so on for additional entries)
+ *
+ * The GUID of each secret entry designates the usage of the secret data.
+ */
+
+/**
+ * struct secret_header - Header of entire secret area; this should be followed
+ * by instances of struct secret_entry.
+ * @guid:	Must be EFI_SEVSECRET_TABLE_HEADER_GUID
+ * @len:	Length in bytes of entire secret area, including header
+ */
+struct secret_header {
+	efi_guid_t guid;
+	u32 len;
+} __attribute((packed));
+
+/**
+ * struct secret_entry - Holds one secret entry
+ * @guid:	Secret-specific GUID
+ * @len:	Length of secret entry, including its guid and len fields
+ * @data:	The secret data
+ */
+struct secret_entry {
+	efi_guid_t guid;
+	u32 len;
+	u8 data[];
+} __attribute((packed));
+
+static struct sev_secret the_sev_secret;
+
+static size_t secret_entry_data_len(struct secret_entry *e)
+{
+	return e->len - sizeof(*e);
+}
+
+static int sev_secret_bin_file_show(struct seq_file *file, void *data)
+{
+	struct secret_entry *e = file->private;
+
+	if (e)
+		seq_write(file, e->data, secret_entry_data_len(e));
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(sev_secret_bin_file);
+
+static inline struct sev_secret *sev_secret_get(void)
+{
+	return &the_sev_secret;
+}
+
+static int sev_secret_map_area(void)
+{
+	struct sev_secret *s = sev_secret_get();
+	struct linux_efi_confidential_computing_secret_area *secret_area;
+	u32 secret_area_size;
+
+	if (efi.confidential_computing_secret == EFI_INVALID_TABLE_ADDR) {
+		pr_err("Secret area address is not available\n");
+		return -EINVAL;
+	}
+
+	secret_area =
+		memremap(efi.confidential_computing_secret, sizeof(*secret_area), MEMREMAP_WB);
+	if (secret_area == NULL) {
+		pr_err("Could not map secret area header\n");
+		return -ENOMEM;
+	}
+
+	secret_area_size = sizeof(*secret_area) + secret_area->size;
+	memunmap(secret_area);
+
+	secret_area = memremap(efi.confidential_computing_secret, secret_area_size, MEMREMAP_WB);
+	if (secret_area == NULL) {
+		pr_err("Could not map secret area\n");
+		return -ENOMEM;
+	}
+
+	s->secret_area = secret_area;
+	return 0;
+}
+
+static void sev_secret_securityfs_teardown(void)
+{
+	struct sev_secret *s = sev_secret_get();
+	int i;
+
+	for (i = (SEV_SECRET_NUM_FILES - 1); i >= 0; i--)
+		if (s->fs_files[i])
+			securityfs_remove(s->fs_files[i]);
+
+	if (s->fs_dir)
+		securityfs_remove(s->fs_dir);
+
+	pr_debug("Removed sev_secret securityfs entries\n");
+}
+
+static int sev_secret_securityfs_setup(void)
+{
+	efi_guid_t tableheader_guid = EFI_SEVSECRET_TABLE_HEADER_GUID;
+	struct sev_secret *s = sev_secret_get();
+	int ret = 0, i = 0, bytes_left;
+	unsigned char *ptr;
+	struct secret_header *h;
+	struct secret_entry *e;
+	struct dentry *dent;
+	char guid_str[EFI_VARIABLE_GUID_LEN + 1];
+
+	s->fs_dir = NULL;
+	memset(s->fs_files, 0, sizeof(s->fs_files));
+
+	dent = securityfs_create_dir("sev_secret", NULL);
+	if (IS_ERR(dent)) {
+		pr_err("Error creating SEV secret securityfs directory entry");
+		return PTR_ERR(dent);
+	}
+	s->fs_dir = dent;
+
+	ptr = s->secret_area->area;
+	h = (struct secret_header *)ptr;
+	if (memcmp(&h->guid, &tableheader_guid, sizeof(h->guid))) {
+		pr_err("SEV secret area does not start with correct GUID\n");
+		ret = -EINVAL;
+		goto err_cleanup;
+	}
+	if (h->len < sizeof(*h)) {
+		pr_err("SEV secret area reported length is too small\n");
+		ret = -EINVAL;
+		goto err_cleanup;
+	}
+
+	bytes_left = h->len - sizeof(*h);
+	ptr += sizeof(*h);
+	while (bytes_left >= (int)sizeof(*e) && i < SEV_SECRET_NUM_FILES) {
+		e = (struct secret_entry *)ptr;
+		if (e->len < sizeof(*e) || e->len > (unsigned int)bytes_left) {
+			pr_err("SEV secret area is corrupted\n");
+			ret = -EINVAL;
+			goto err_cleanup;
+		}
+
+		efi_guid_to_str(&e->guid, guid_str);
+
+		dent = securityfs_create_file(guid_str, 0440, s->fs_dir, (void *)e,
+					      &sev_secret_bin_file_fops);
+		if (IS_ERR(dent)) {
+			pr_err("Error creating SEV secret securityfs entry\n");
+			ret = PTR_ERR(dent);
+			goto err_cleanup;
+		}
+
+		s->fs_files[i++] = dent;
+		ptr += e->len;
+		bytes_left -= e->len;
+	}
+
+	pr_debug("Created %d entries in sev_secret securityfs\n", i);
+	return 0;
+
+err_cleanup:
+	sev_secret_securityfs_teardown();
+	return ret;
+}
+
+static void sev_secret_unmap_area(void)
+{
+	struct sev_secret *s = sev_secret_get();
+
+	if (s->secret_area) {
+		memunmap(s->secret_area);
+		s->secret_area = NULL;
+	}
+}
+
+static int __init sev_secret_init(void)
+{
+	int ret;
+
+	ret = sev_secret_map_area();
+	if (ret)
+		return ret;
+
+	ret = sev_secret_securityfs_setup();
+	if (ret)
+		goto err_unmap;
+
+	return ret;
+
+err_unmap:
+	sev_secret_unmap_area();
+	return ret;
+}
+
+static void __exit sev_secret_exit(void)
+{
+	sev_secret_securityfs_teardown();
+	sev_secret_unmap_area();
+}
+
+module_init(sev_secret_init);
+module_exit(sev_secret_exit);
+
+MODULE_DESCRIPTION("AMD SEV confidential computing secret area access");
+MODULE_AUTHOR("IBM");
+MODULE_LICENSE("GPL");