From patchwork Wed Nov 16 16:16:40 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Jason A. 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Donenfeld" To: linux-efi@vger.kernel.org, linux-crypto@vger.kernel.org Cc: "Jason A. Donenfeld" , Ard Biesheuvel , Lennart Poettering Subject: [PATCH RFC v1 4/6] efi: stub: use random seed from EFI variable Date: Wed, 16 Nov 2022 17:16:40 +0100 Message-Id: <20221116161642.1670235-5-Jason@zx2c4.com> In-Reply-To: <20221116161642.1670235-1-Jason@zx2c4.com> References: <20221116161642.1670235-1-Jason@zx2c4.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org Since we have some storage, we can manage non-volatile seeds directly from EFISTUB. This commit passes the contents of an EFI variable to the kernel via the existing configuration table. Signed-off-by: Jason A. Donenfeld --- drivers/firmware/efi/libstub/random.c | 59 +++++++++++++++++++++------ include/linux/efi.h | 1 + 2 files changed, 48 insertions(+), 12 deletions(-) diff --git a/drivers/firmware/efi/libstub/random.c b/drivers/firmware/efi/libstub/random.c index f85d2c066877..1e72013a6457 100644 --- a/drivers/firmware/efi/libstub/random.c +++ b/drivers/firmware/efi/libstub/random.c @@ -67,14 +67,25 @@ efi_status_t efi_random_get_seed(void) efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID; efi_guid_t rng_algo_raw = EFI_RNG_ALGORITHM_RAW; efi_guid_t rng_table_guid = LINUX_EFI_RANDOM_SEED_TABLE_GUID; + efi_char16_t rng_nv_seed_var[] = LINUX_EFI_RANDOM_NV_SEED_VAR; struct linux_efi_random_seed *prev_seed, *seed = NULL; - int prev_seed_size = 0, seed_size = EFI_RANDOM_SEED_SIZE; + u8 nv_seed[EFI_RANDOM_SEED_SIZE]; + unsigned long prev_seed_size = 0, nv_seed_size = sizeof(nv_seed), seed_size = 0, offset = 0; efi_rng_protocol_t *rng = NULL; efi_status_t status; status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng); - if (status != EFI_SUCCESS) - return status; + if (status == EFI_SUCCESS) + seed_size += EFI_RANDOM_SEED_SIZE; + + status = get_efi_var(rng_nv_seed_var, &rng_table_guid, NULL, &nv_seed_size, nv_seed); + if (status == EFI_SUCCESS) + seed_size += nv_seed_size; + else + nv_seed_size = 0; + + if (!seed_size) + return EFI_NOT_FOUND; /* * Check whether a seed was provided by a prior boot stage. In that @@ -83,7 +94,7 @@ efi_status_t efi_random_get_seed(void) * Note that we should read the seed size with caution, in case the * table got corrupted in memory somehow. */ - prev_seed = get_efi_config_table(LINUX_EFI_RANDOM_SEED_TABLE_GUID); + prev_seed = get_efi_config_table(rng_table_guid); if (prev_seed && prev_seed->size <= 512U) { prev_seed_size = prev_seed->size; seed_size += prev_seed_size; @@ -103,7 +114,7 @@ efi_status_t efi_random_get_seed(void) } status = efi_call_proto(rng, get_rng, &rng_algo_raw, - EFI_RANDOM_SEED_SIZE, seed->bits); + EFI_RANDOM_SEED_SIZE, seed->bits + offset); if (status == EFI_UNSUPPORTED) /* @@ -111,16 +122,40 @@ efi_status_t efi_random_get_seed(void) * is not implemented. */ status = efi_call_proto(rng, get_rng, NULL, - EFI_RANDOM_SEED_SIZE, seed->bits); + EFI_RANDOM_SEED_SIZE, seed->bits + offset); - if (status != EFI_SUCCESS) + if (status == EFI_SUCCESS) + offset += EFI_RANDOM_SEED_SIZE; + + if (nv_seed_size) { + memcpy(seed->bits + offset, nv_seed, nv_seed_size); + memzero_explicit(nv_seed, nv_seed_size); + /* + * Zero it out before committing to using it. TODO: in the + * future, maybe we can hash it forward instead, which is + * better and also reduces the amount of writes here. + */ + status = set_efi_var(rng_nv_seed_var, &rng_table_guid, + EFI_VARIABLE_NON_VOLATILE | + EFI_VARIABLE_BOOTSERVICE_ACCESS | + EFI_VARIABLE_RUNTIME_ACCESS, nv_seed_size, nv_seed); + if (status == EFI_SUCCESS) + status = set_efi_var(rng_nv_seed_var, &rng_table_guid, 0, 0, NULL); + if (status == EFI_SUCCESS) + offset += nv_seed_size; + else + memzero_explicit(seed->bits + offset, nv_seed_size); + } + + if (!offset) goto err_freepool; - seed->size = seed_size; - if (prev_seed_size) - memcpy(seed->bits + EFI_RANDOM_SEED_SIZE, prev_seed->bits, - prev_seed_size); + if (prev_seed_size) { + memcpy(seed->bits + offset, prev_seed->bits, prev_seed_size); + offset += prev_seed_size; + } + seed->size = offset; status = efi_bs_call(install_configuration_table, &rng_table_guid, seed); if (status != EFI_SUCCESS) goto err_freepool; @@ -135,7 +170,7 @@ efi_status_t efi_random_get_seed(void) err_freepool: memzero_explicit(seed, struct_size(seed, bits, seed_size)); efi_bs_call(free_pool, seed); - efi_warn("Failed to obtain seed from EFI_RNG_PROTOCOL\n"); + efi_warn("Failed to obtain seed from EFI_RNG_PROTOCOL and EFI variable\n"); err_warn: if (prev_seed) efi_warn("Retaining bootloader-supplied seed only"); diff --git a/include/linux/efi.h b/include/linux/efi.h index 4aa1dbc7b064..0e93510b23b5 100644 --- a/include/linux/efi.h +++ b/include/linux/efi.h @@ -408,6 +408,7 @@ void efi_native_runtime_setup(void); #define LINUX_EFI_ARM_CPU_STATE_TABLE_GUID EFI_GUID(0xef79e4aa, 0x3c3d, 0x4989, 0xb9, 0x02, 0x07, 0xa9, 0x43, 0xe5, 0x50, 0xd2) #define LINUX_EFI_LOADER_ENTRY_GUID EFI_GUID(0x4a67b082, 0x0a4c, 0x41cf, 0xb6, 0xc7, 0x44, 0x0b, 0x29, 0xbb, 0x8c, 0x4f) #define LINUX_EFI_RANDOM_SEED_TABLE_GUID EFI_GUID(0x1ce1e5bc, 0x7ceb, 0x42f2, 0x81, 0xe5, 0x8a, 0xad, 0xf1, 0x80, 0xf5, 0x7b) +#define LINUX_EFI_RANDOM_NV_SEED_VAR L"RandomNVSeed" #define LINUX_EFI_TPM_EVENT_LOG_GUID EFI_GUID(0xb7799cb0, 0xeca2, 0x4943, 0x96, 0x67, 0x1f, 0xae, 0x07, 0xb7, 0x47, 0xfa) #define LINUX_EFI_TPM_FINAL_LOG_GUID EFI_GUID(0x1e2ed096, 0x30e2, 0x4254, 0xbd, 0x89, 0x86, 0x3b, 0xbe, 0xf8, 0x23, 0x25) #define LINUX_EFI_MEMRESERVE_TABLE_GUID EFI_GUID(0x888eb0c6, 0x8ede, 0x4ff5, 0xa8, 0xf0, 0x9a, 0xee, 0x5c, 0xb9, 0x77, 0xc2)