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 <Jason@xxxxxxxxx>
---
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)
--
2.38.1
