efi_guid_t rng_table_guid = LINUX_EFI_RANDOM_SEED_TABLE_GUID;
struct linux_efi_random_seed *prev_seed, *seed = NULL;
int prev_seed_size = 0, seed_size = EFI_RANDOM_SEED_SIZE;
+ unsigned long nv_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)
+ seed_size = 0;
+
+ // Call GetVariable() with a zero length buffer to obtain the size
+ get_efi_var(L"RandomSeed", &rng_table_guid, NULL, &nv_seed_size, NULL);
+ if (!seed_size && !nv_seed_size)
return status;
+ seed_size += nv_seed_size;
+
/*
* Check whether a seed was provided by a prior boot stage. In that
* case, instead of overwriting it, let's create a new buffer that can
* 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;
goto err_warn;
}
- status = efi_call_proto(rng, get_rng, &rng_algo_raw,
- EFI_RANDOM_SEED_SIZE, seed->bits);
-
- if (status == EFI_UNSUPPORTED)
- /*
- * Use whatever algorithm we have available if the raw algorithm
- * is not implemented.
- */
- status = efi_call_proto(rng, get_rng, NULL,
+ if (rng) {
+ status = efi_call_proto(rng, get_rng, &rng_algo_raw,
EFI_RANDOM_SEED_SIZE, seed->bits);
- if (status != EFI_SUCCESS)
+ if (status == EFI_UNSUPPORTED)
+ /*
+ * Use whatever algorithm we have available if the raw algorithm
+ * is not implemented.
+ */
+ status = efi_call_proto(rng, get_rng, NULL,
+ EFI_RANDOM_SEED_SIZE, seed->bits);
+
+ if (status == EFI_SUCCESS)
+ offset = EFI_RANDOM_SEED_SIZE;
+ }
+
+ if (nv_seed_size) {
+ status = get_efi_var(L"RandomSeed", &rng_table_guid, NULL,
+ &nv_seed_size, seed->bits + offset);
+
+ if (status == EFI_SUCCESS)
+ /*
+ * We delete the seed here, and /hope/ that this causes
+ * EFI to also zero out its representation on disk.
+ * This is somewhat idealistic, but overwriting the
+ * variable with zeros is likely just as fraught too.
+ * TODO: in the future, maybe we can hash it forward
+ * instead, and write a new seed.
+ */
+ status = set_efi_var(L"RandomSeed", &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;
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 or EFI variable\n");
err_warn:
if (prev_seed)
efi_warn("Retaining bootloader-supplied seed only");