diff options
Diffstat (limited to 'src/boot/efi/random-seed.c')
| -rw-r--r-- | src/boot/efi/random-seed.c | 328 |
1 files changed, 328 insertions, 0 deletions
diff --git a/src/boot/efi/random-seed.c b/src/boot/efi/random-seed.c new file mode 100644 index 0000000..eda9260 --- /dev/null +++ b/src/boot/efi/random-seed.c @@ -0,0 +1,328 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <efi.h> +#include <efilib.h> + +#include "missing_efi.h" +#include "random-seed.h" +#include "sha256.h" +#include "util.h" +#include "shim.h" + +#define RANDOM_MAX_SIZE_MIN (32U) +#define RANDOM_MAX_SIZE_MAX (32U*1024U) + +static const EFI_GUID rng_protocol_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; + + /* Try to acquire the specified number of bytes from the UEFI RNG */ + + err = LibLocateProtocol((EFI_GUID*) &rng_protocol_guid, (VOID**) &rng); + if (EFI_ERROR(err)) + return err; + if (!rng) + return EFI_UNSUPPORTED; + + data = AllocatePool(size); + if (!data) + return log_oom(); + + err = uefi_call_wrapper(rng->GetRNG, 3, rng, NULL, size, data); + if (EFI_ERROR(err)) { + Print(L"Failed to acquire RNG data: %r\n", err); + return 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; + + 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; + UINTN i; + + /* Hashes the specified parameters in counter mode, generating n hash values, with the counter in the + * range counter_start…counter_start+n-1. */ + + output = AllocatePool(n * HASH_VALUE_SIZE); + if (!output) + return log_oom(); + + for (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; + + /* 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; +} + +EFI_STATUS acquire_system_token(VOID **ret, UINTN *ret_size) { + _cleanup_freepool_ CHAR8 *data = NULL; + EFI_STATUS err; + UINTN size; + + err = efivar_get_raw(&loader_guid, L"LoaderSystemToken", &data, &size); + if (EFI_ERROR(err)) { + if (err != EFI_NOT_FOUND) + Print(L"Failed to read LoaderSystemToken EFI variable: %r", err); + return err; + } + + if (size <= 0) { + Print(L"System token too short, ignoring."); + return EFI_NOT_FOUND; + } + + *ret = TAKE_PTR(data); + *ret_size = size; + + return EFI_SUCCESS; +} + +static VOID validate_sha256(void) { + +#ifndef __OPTIMIZE__ + /* 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 }}, + }; + + UINTN i; + + for (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); + + if (CompareMem(result, array[i].hash, HASH_VALUE_SIZE) != 0) { + Print(L"SHA256 failed validation.\n"); + uefi_call_wrapper(BS->Stall, 1, 120 * 1000 * 1000); + return; + } + } + + Print(L"SHA256 validated\n"); +#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; + + 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 = uefi_call_wrapper(root_dir->Open, 5, root_dir, &handle, L"\\loader\\random-seed", EFI_FILE_MODE_READ|EFI_FILE_MODE_WRITE, 0ULL); + if (EFI_ERROR(err)) { + if (err != EFI_NOT_FOUND) + Print(L"Failed to open random seed file: %r\n", err); + return err; + } + + info = LibFileInfo(handle); + if (!info) + return log_oom(); + + size = info->FileSize; + if (size < RANDOM_MAX_SIZE_MIN) { + Print(L"Random seed file is too short?\n"); + return EFI_INVALID_PARAMETER; + } + + if (size > RANDOM_MAX_SIZE_MAX) { + Print(L"Random seed file is too large?\n"); + return EFI_INVALID_PARAMETER; + } + + seed = AllocatePool(size); + if (!seed) + return log_oom(); + + rsize = size; + err = uefi_call_wrapper(handle->Read, 3, handle, &rsize, seed); + if (EFI_ERROR(err)) { + Print(L"Failed to read random seed file: %r\n", err); + return err; + } + if (rsize != size) { + Print(L"Short read on random seed file\n"); + return EFI_PROTOCOL_ERROR; + } + + err = uefi_call_wrapper(handle->SetPosition, 2, handle, 0); + if (EFI_ERROR(err)) { + Print(L"Failed to seek to beginning of random seed file: %r\n", err); + return 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 = uefi_call_wrapper(handle->Write, 3, handle, &wsize, new_seed); + if (EFI_ERROR(err)) { + Print(L"Failed to write random seed file: %r\n", err); + return err; + } + if (wsize != size) { + Print(L"Short write on random seed file\n"); + return EFI_PROTOCOL_ERROR; + } + + err = uefi_call_wrapper(handle->Flush, 1, handle); + if (EFI_ERROR(err)) { + Print(L"Failed to flush random seed file: %r\n"); + return err; + } + + /* We are good to go */ + err = efivar_set_raw(&loader_guid, L"LoaderRandomSeed", for_kernel, size, FALSE); + if (EFI_ERROR(err)) { + Print(L"Failed to write random seed to EFI variable: %r\n", err); + return err; + } + + return EFI_SUCCESS; +} |