write in 30M

hc

2024-02-20 ea08eeccae9297f7aabd2ef7f0c2517ac4549acc

 kernel/drivers/firmware/efi/libstub/random.c
..
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@@ -67,8 +67,9 @@
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 	efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
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 	efi_guid_t rng_algo_raw = EFI_RNG_ALGORITHM_RAW;
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 	efi_guid_t rng_table_guid = LINUX_EFI_RANDOM_SEED_TABLE_GUID;
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+	struct linux_efi_random_seed *prev_seed, *seed = NULL;
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+	int prev_seed_size = 0, seed_size = EFI_RANDOM_SEED_SIZE;
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 	efi_rng_protocol_t *rng = NULL;
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-	struct linux_efi_random_seed *seed = NULL;
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 	efi_status_t status;
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 	status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng);
..
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@@ -76,18 +77,33 @@
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 		return status;
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 	/*
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+	 * Check whether a seed was provided by a prior boot stage. In that
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+	 * case, instead of overwriting it, let's create a new buffer that can
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+	 * hold both, and concatenate the existing and the new seeds.
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+	 * Note that we should read the seed size with caution, in case the
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+	 * table got corrupted in memory somehow.
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+	 */
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+	prev_seed = get_efi_config_table(LINUX_EFI_RANDOM_SEED_TABLE_GUID);
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+	if (prev_seed && prev_seed->size <= 512U) {
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+		prev_seed_size = prev_seed->size;
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+		seed_size += prev_seed_size;
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+	}
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+
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+	/*
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 	 * Use EFI_ACPI_RECLAIM_MEMORY here so that it is guaranteed that the
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 	 * allocation will survive a kexec reboot (although we refresh the seed
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 	 * beforehand)
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 	 */
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 	status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY,
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-			     sizeof(*seed) + EFI_RANDOM_SEED_SIZE,
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+			     struct_size(seed, bits, seed_size),
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 			     (void **)&seed);
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-	if (status != EFI_SUCCESS)
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-		return status;
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+	if (status != EFI_SUCCESS) {
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+		efi_warn("Failed to allocate memory for RNG seed.\n");
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+		goto err_warn;
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+	}
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 	status = efi_call_proto(rng, get_rng, &rng_algo_raw,
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-				 EFI_RANDOM_SEED_SIZE, seed->bits);
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+				EFI_RANDOM_SEED_SIZE, seed->bits);
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 	if (status == EFI_UNSUPPORTED)
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 		/*
..
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@@ -100,14 +116,28 @@
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 	if (status != EFI_SUCCESS)
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 		goto err_freepool;
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-	seed->size = EFI_RANDOM_SEED_SIZE;
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+	seed->size = seed_size;
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+	if (prev_seed_size)
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+		memcpy(seed->bits + EFI_RANDOM_SEED_SIZE, prev_seed->bits,
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+		       prev_seed_size);
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+
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 	status = efi_bs_call(install_configuration_table, &rng_table_guid, seed);
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 	if (status != EFI_SUCCESS)
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 		goto err_freepool;
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+	if (prev_seed_size) {
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+		/* wipe and free the old seed if we managed to install the new one */
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+		memzero_explicit(prev_seed->bits, prev_seed_size);
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+		efi_bs_call(free_pool, prev_seed);
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+	}
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 	return EFI_SUCCESS;
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 err_freepool:
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+	memzero_explicit(seed, struct_size(seed, bits, seed_size));
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 	efi_bs_call(free_pool, seed);
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+	efi_warn("Failed to obtain seed from EFI_RNG_PROTOCOL\n");
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+err_warn:
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+	if (prev_seed)
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+		efi_warn("Retaining bootloader-supplied seed only");
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 	return status;
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 }