diff options
Diffstat (limited to 'drivers/firmware/efi/libstub/random.c')
| -rw-r--r-- | drivers/firmware/efi/libstub/random.c | 179 |
1 files changed, 179 insertions, 0 deletions
diff --git a/drivers/firmware/efi/libstub/random.c b/drivers/firmware/efi/libstub/random.c new file mode 100644 index 0000000000..7109b8a2dc --- /dev/null +++ b/drivers/firmware/efi/libstub/random.c @@ -0,0 +1,179 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2016 Linaro Ltd; <ard.biesheuvel@linaro.org> + */ + +#include <linux/efi.h> +#include <asm/efi.h> + +#include "efistub.h" + +typedef union efi_rng_protocol efi_rng_protocol_t; + +union efi_rng_protocol { + struct { + efi_status_t (__efiapi *get_info)(efi_rng_protocol_t *, + unsigned long *, + efi_guid_t *); + efi_status_t (__efiapi *get_rng)(efi_rng_protocol_t *, + efi_guid_t *, unsigned long, + u8 *out); + }; + struct { + u32 get_info; + u32 get_rng; + } mixed_mode; +}; + +/** + * efi_get_random_bytes() - fill a buffer with random bytes + * @size: size of the buffer + * @out: caller allocated buffer to receive the random bytes + * + * The call will fail if either the firmware does not implement the + * EFI_RNG_PROTOCOL or there are not enough random bytes available to fill + * the buffer. + * + * Return: status code + */ +efi_status_t efi_get_random_bytes(unsigned long size, u8 *out) +{ + efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID; + efi_status_t status; + efi_rng_protocol_t *rng = NULL; + + status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng); + if (status != EFI_SUCCESS) + return status; + + return efi_call_proto(rng, get_rng, NULL, size, out); +} + +/** + * efi_random_get_seed() - provide random seed as configuration table + * + * The EFI_RNG_PROTOCOL is used to read random bytes. These random bytes are + * saved as a configuration table which can be used as entropy by the kernel + * for the initialization of its pseudo random number generator. + * + * If the EFI_RNG_PROTOCOL is not available or there are not enough random bytes + * available, the configuration table will not be installed and an error code + * will be returned. + * + * Return: status code + */ +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; + 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 + * 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(rng_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, + struct_size(seed, bits, seed_size), + (void **)&seed); + if (status != EFI_SUCCESS) { + efi_warn("Failed to allocate memory for RNG seed.\n"); + goto err_warn; + } + + if (rng) { + 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, + 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; + + 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; + + 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 or EFI variable\n"); +err_warn: + if (prev_seed) + efi_warn("Retaining bootloader-supplied seed only"); + return status; +} |