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/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include <efi.h>
#include <efilib.h>
#include "missing_efi.h"
#include "random-seed.h"
#include "secure-boot.h"
#include "sha256.h"
#include "util.h"
#define RANDOM_MAX_SIZE_MIN (32U)
#define RANDOM_MAX_SIZE_MAX (32U*1024U)
#define EFI_RNG_GUID &(const EFI_GUID) EFI_RNG_PROTOCOL_GUID
/* SHA256 gives us 256/8=32 bytes */
#define HASH_VALUE_SIZE 32
static EFI_STATUS acquire_rng(UINTN size, void **ret) {
_cleanup_freepool_ void *data = NULL;
EFI_RNG_PROTOCOL *rng;
EFI_STATUS err;
assert(ret);
/* Try to acquire the specified number of bytes from the UEFI RNG */
err = LibLocateProtocol((EFI_GUID*) EFI_RNG_GUID, (void**) &rng);
if (EFI_ERROR(err))
return err;
if (!rng)
return EFI_UNSUPPORTED;
data = xallocate_pool(size);
err = rng->GetRNG(rng, NULL, size, data);
if (EFI_ERROR(err))
return log_error_status_stall(err, L"Failed to acquire RNG data: %r", err);
*ret = TAKE_PTR(data);
return EFI_SUCCESS;
}
static void hash_once(
const void *old_seed,
const void *rng,
UINTN size,
const void *system_token,
UINTN system_token_size,
UINTN counter,
UINT8 ret[static HASH_VALUE_SIZE]) {
/* This hashes together:
*
* 1. The contents of the old seed file
* 2. Some random data acquired from the UEFI RNG (optional)
* 3. Some 'system token' the installer installed as EFI variable (optional)
* 4. A counter value
*
* And writes the result to the specified buffer.
*/
struct sha256_ctx hash;
assert(old_seed);
assert(system_token_size == 0 || system_token);
sha256_init_ctx(&hash);
sha256_process_bytes(old_seed, size, &hash);
if (rng)
sha256_process_bytes(rng, size, &hash);
if (system_token_size > 0)
sha256_process_bytes(system_token, system_token_size, &hash);
sha256_process_bytes(&counter, sizeof(counter), &hash);
sha256_finish_ctx(&hash, ret);
}
static EFI_STATUS hash_many(
const void *old_seed,
const void *rng,
UINTN size,
const void *system_token,
UINTN system_token_size,
UINTN counter_start,
UINTN n,
void **ret) {
_cleanup_freepool_ void *output = NULL;
assert(old_seed);
assert(system_token_size == 0 || system_token);
assert(ret);
/* Hashes the specified parameters in counter mode, generating n hash values, with the counter in the
* range counter_start…counter_start+n-1. */
output = xallocate_pool(n * HASH_VALUE_SIZE);
for (UINTN i = 0; i < n; i++)
hash_once(old_seed, rng, size,
system_token, system_token_size,
counter_start + i,
(UINT8*) output + (i * HASH_VALUE_SIZE));
*ret = TAKE_PTR(output);
return EFI_SUCCESS;
}
static EFI_STATUS mangle_random_seed(
const void *old_seed,
const void *rng,
UINTN size,
const void *system_token,
UINTN system_token_size,
void **ret_new_seed,
void **ret_for_kernel) {
_cleanup_freepool_ void *new_seed = NULL, *for_kernel = NULL;
EFI_STATUS err;
UINTN n;
assert(old_seed);
assert(system_token_size == 0 || system_token);
assert(ret_new_seed);
assert(ret_for_kernel);
/* This takes the old seed file contents, an (optional) random number acquired from the UEFI RNG, an
* (optional) system 'token' installed once by the OS installer in an EFI variable, and hashes them
* together in counter mode, generating a new seed (to replace the file on disk) and the seed for the
* kernel. To keep things simple, the new seed and kernel data have the same size as the old seed and
* RNG data. */
n = (size + HASH_VALUE_SIZE - 1) / HASH_VALUE_SIZE;
/* Begin hashing in counter mode at counter 0 for the new seed for the disk */
err = hash_many(old_seed, rng, size, system_token, system_token_size, 0, n, &new_seed);
if (EFI_ERROR(err))
return err;
/* Continue counting at 'n' for the seed for the kernel */
err = hash_many(old_seed, rng, size, system_token, system_token_size, n, n, &for_kernel);
if (EFI_ERROR(err))
return err;
*ret_new_seed = TAKE_PTR(new_seed);
*ret_for_kernel = TAKE_PTR(for_kernel);
return EFI_SUCCESS;
}
static EFI_STATUS acquire_system_token(void **ret, UINTN *ret_size) {
_cleanup_freepool_ CHAR8 *data = NULL;
EFI_STATUS err;
UINTN size;
assert(ret);
assert(ret_size);
err = efivar_get_raw(LOADER_GUID, L"LoaderSystemToken", &data, &size);
if (EFI_ERROR(err)) {
if (err != EFI_NOT_FOUND)
log_error_stall(L"Failed to read LoaderSystemToken EFI variable: %r", err);
return err;
}
if (size <= 0)
return log_error_status_stall(EFI_NOT_FOUND, L"System token too short, ignoring.");
*ret = TAKE_PTR(data);
*ret_size = size;
return EFI_SUCCESS;
}
static void validate_sha256(void) {
#ifdef EFI_DEBUG
/* Let's validate our SHA256 implementation. We stole it from glibc, and converted it to UEFI
* style. We better check whether it does the right stuff. We use the simpler test vectors from the
* SHA spec. Note that we strip this out in optimization builds. */
static const struct {
const char *string;
uint8_t hash[HASH_VALUE_SIZE];
} array[] = {
{ "abc",
{ 0xba, 0x78, 0x16, 0xbf, 0x8f, 0x01, 0xcf, 0xea,
0x41, 0x41, 0x40, 0xde, 0x5d, 0xae, 0x22, 0x23,
0xb0, 0x03, 0x61, 0xa3, 0x96, 0x17, 0x7a, 0x9c,
0xb4, 0x10, 0xff, 0x61, 0xf2, 0x00, 0x15, 0xad }},
{ "",
{ 0xe3, 0xb0, 0xc4, 0x42, 0x98, 0xfc, 0x1c, 0x14,
0x9a, 0xfb, 0xf4, 0xc8, 0x99, 0x6f, 0xb9, 0x24,
0x27, 0xae, 0x41, 0xe4, 0x64, 0x9b, 0x93, 0x4c,
0xa4, 0x95, 0x99, 0x1b, 0x78, 0x52, 0xb8, 0x55 }},
{ "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq",
{ 0x24, 0x8d, 0x6a, 0x61, 0xd2, 0x06, 0x38, 0xb8,
0xe5, 0xc0, 0x26, 0x93, 0x0c, 0x3e, 0x60, 0x39,
0xa3, 0x3c, 0xe4, 0x59, 0x64, 0xff, 0x21, 0x67,
0xf6, 0xec, 0xed, 0xd4, 0x19, 0xdb, 0x06, 0xc1 }},
{ "abcdefghbcdefghicdefghijdefghijkefghijklfghijklmghijklmnhijklmnoijklmnopjklmnopqklmnopqrlmnopqrsmnopqrstnopqrstu",
{ 0xcf, 0x5b, 0x16, 0xa7, 0x78, 0xaf, 0x83, 0x80,
0x03, 0x6c, 0xe5, 0x9e, 0x7b, 0x04, 0x92, 0x37,
0x0b, 0x24, 0x9b, 0x11, 0xe8, 0xf0, 0x7a, 0x51,
0xaf, 0xac, 0x45, 0x03, 0x7a, 0xfe, 0xe9, 0xd1 }},
};
for (UINTN i = 0; i < ELEMENTSOF(array); i++) {
struct sha256_ctx hash;
uint8_t result[HASH_VALUE_SIZE];
sha256_init_ctx(&hash);
sha256_process_bytes(array[i].string, strlena((const CHAR8*) array[i].string), &hash);
sha256_finish_ctx(&hash, result);
assert(CompareMem(result, array[i].hash, HASH_VALUE_SIZE) == 0);
}
#endif
}
EFI_STATUS process_random_seed(EFI_FILE *root_dir, RandomSeedMode mode) {
_cleanup_freepool_ void *seed = NULL, *new_seed = NULL, *rng = NULL, *for_kernel = NULL, *system_token = NULL;
_cleanup_(FileHandleClosep) EFI_FILE_HANDLE handle = NULL;
UINTN size, rsize, wsize, system_token_size = 0;
_cleanup_freepool_ EFI_FILE_INFO *info = NULL;
EFI_STATUS err;
assert(root_dir);
validate_sha256();
if (mode == RANDOM_SEED_OFF)
return EFI_NOT_FOUND;
/* Let's better be safe than sorry, and for now disable this logic in SecureBoot mode, so that we
* don't credit a random seed that is not authenticated. */
if (secure_boot_enabled())
return EFI_NOT_FOUND;
/* Get some system specific seed that the installer might have placed in an EFI variable. We include
* it in our hash. This is protection against golden master image sloppiness, and it remains on the
* system, even when disk images are duplicated or swapped out. */
err = acquire_system_token(&system_token, &system_token_size);
if (mode != RANDOM_SEED_ALWAYS && EFI_ERROR(err))
return err;
err = root_dir->Open(root_dir, &handle, (CHAR16*) L"\\loader\\random-seed", EFI_FILE_MODE_READ|EFI_FILE_MODE_WRITE, 0ULL);
if (EFI_ERROR(err)) {
if (err != EFI_NOT_FOUND && err != EFI_WRITE_PROTECTED)
log_error_stall(L"Failed to open random seed file: %r", err);
return err;
}
err = get_file_info_harder(handle, &info, NULL);
if (EFI_ERROR(err))
return log_error_status_stall(err, L"Failed to get file info for random seed: %r");
size = info->FileSize;
if (size < RANDOM_MAX_SIZE_MIN)
return log_error_status_stall(EFI_INVALID_PARAMETER, L"Random seed file is too short.");
if (size > RANDOM_MAX_SIZE_MAX)
return log_error_status_stall(EFI_INVALID_PARAMETER, L"Random seed file is too large.");
seed = xallocate_pool(size);
rsize = size;
err = handle->Read(handle, &rsize, seed);
if (EFI_ERROR(err))
return log_error_status_stall(err, L"Failed to read random seed file: %r", err);
if (rsize != size)
return log_error_status_stall(EFI_PROTOCOL_ERROR, L"Short read on random seed file.");
err = handle->SetPosition(handle, 0);
if (EFI_ERROR(err))
return log_error_status_stall(err, L"Failed to seek to beginning of random seed file: %r", err);
/* Request some random data from the UEFI RNG. We don't need this to work safely, but it's a good
* idea to use it because it helps us for cases where users mistakenly include a random seed in
* golden master images that are replicated many times. */
(void) acquire_rng(size, &rng); /* It's fine if this fails */
/* Calculate new random seed for the disk and what to pass to the kernel */
err = mangle_random_seed(seed, rng, size, system_token, system_token_size, &new_seed, &for_kernel);
if (EFI_ERROR(err))
return err;
/* Update the random seed on disk before we use it */
wsize = size;
err = handle->Write(handle, &wsize, new_seed);
if (EFI_ERROR(err))
return log_error_status_stall(err, L"Failed to write random seed file: %r", err);
if (wsize != size)
return log_error_status_stall(EFI_PROTOCOL_ERROR, L"Short write on random seed file.");
err = handle->Flush(handle);
if (EFI_ERROR(err))
return log_error_status_stall(err, L"Failed to flush random seed file: %r", err);
/* We are good to go */
err = efivar_set_raw(LOADER_GUID, L"LoaderRandomSeed", for_kernel, size, 0);
if (EFI_ERROR(err))
return log_error_status_stall(err, L"Failed to write random seed to EFI variable: %r", err);
return EFI_SUCCESS;
}
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