1 files changed, 36 insertions, 6 deletions

diff --git a/drivers/firmware/efi/libstub/random.c b/drivers/firmware/efi/libstub/random.c
index 33ab56769595..f85d2c066877 100644
--- a/drivers/firmware/efi/libstub/random.c
+++ b/drivers/firmware/efi/libstub/random.c
@@ -67,8 +67,9 @@ 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;
+	struct linux_efi_random_seed *prev_seed, *seed = NULL;
+	int prev_seed_size = 0, seed_size = EFI_RANDOM_SEED_SIZE;
 	efi_rng_protocol_t *rng = NULL;
-	struct linux_efi_random_seed *seed = NULL;
 	efi_status_t status;
 
 	status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
@@ -76,18 +77,33 @@ efi_status_t efi_random_get_seed(void)
 		return status;
 
 	/*
+	 * 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
+	 * hold both, and concatenate the existing and the new seeds.
+	 * 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);
+	if (prev_seed && prev_seed->size <= 512U) {
+		prev_seed_size = prev_seed->size;
+		seed_size += prev_seed_size;
+	}
+
+	/*
 	 * Use EFI_ACPI_RECLAIM_MEMORY here so that it is guaranteed that the
 	 * allocation will survive a kexec reboot (although we refresh the seed
 	 * beforehand)
 	 */
 	status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
-			     sizeof(*seed) + EFI_RANDOM_SEED_SIZE,
+			     struct_size(seed, bits, seed_size),
 			     (void **)&seed);
-	if (status != EFI_SUCCESS)
-		return status;
+	if (status != EFI_SUCCESS) {
+		efi_warn("Failed to allocate memory for RNG seed.\n");
+		goto err_warn;
+	}
 
 	status = efi_call_proto(rng, get_rng, &rng_algo_raw,
-				 EFI_RANDOM_SEED_SIZE, seed->bits);
+				EFI_RANDOM_SEED_SIZE, seed->bits);
 
 	if (status == EFI_UNSUPPORTED)
 		/*
@@ -100,14 +116,28 @@ efi_status_t efi_random_get_seed(void)
 	if (status != EFI_SUCCESS)
 		goto err_freepool;
 
-	seed->size = EFI_RANDOM_SEED_SIZE;
+	seed->size = seed_size;
+	if (prev_seed_size)
+		memcpy(seed->bits + EFI_RANDOM_SEED_SIZE, prev_seed->bits,
+		       prev_seed_size);
+
 	status = efi_bs_call(install_configuration_table, &rng_table_guid, seed);
 	if (status != EFI_SUCCESS)
 		goto err_freepool;
 
+	if (prev_seed_size) {
+		/* wipe and free the old seed if we managed to install the new one */
+		memzero_explicit(prev_seed->bits, prev_seed_size);
+		efi_bs_call(free_pool, prev_seed);
+	}
 	return EFI_SUCCESS;
 
 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");
+err_warn:
+	if (prev_seed)
+		efi_warn("Retaining bootloader-supplied seed only");
 	return status;
 }