On Wed, 16 Nov 2022 at 21:06, Jason A. Donenfeld Jason@zx2c4.com wrote:
Taking the minimum is wrong, if the bootloader or EFI stub is actually passing on a bunch of bytes that it expects the kernel to hash itself.
We still need some kind of limit, just so things don't explode if seed->size is bogus.
Ideally, a bootloader will hash it for us, but STUB won't do that, so we should map all the bytes. Also, all those bytes must be zeroed out after use to preserve forward secrecy.
Fixes: 161a438d730d ("efi: random: reduce seed size to 32 bytes") Cc: stable@vger.kernel.org # v4.14+ Cc: Ard Biesheuvel ardb@kernel.org Cc: Ilias Apalodimas ilias.apalodimas@linaro.org Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com
drivers/firmware/efi/efi.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c index f73709f7589a..819409b7b43b 100644 --- a/drivers/firmware/efi/efi.c +++ b/drivers/firmware/efi/efi.c @@ -630,7 +630,7 @@ int __init efi_config_parse_tables(const efi_config_table_t *config_tables,
seed = early_memremap(efi_rng_seed, sizeof(*seed)); if (seed != NULL) {
size = min(seed->size, EFI_RANDOM_SEED_SIZE);
size = seed->size; early_memunmap(seed, sizeof(*seed)); } else { pr_err("Could not map UEFI random seed!\n");@@ -641,6 +641,7 @@ int __init efi_config_parse_tables(const efi_config_table_t *config_tables, if (seed != NULL) { pr_notice("seeding entropy pool\n"); add_bootloader_randomness(seed->bits, size);
memzero_explicit(seed->bits, size); early_memunmap(seed, sizeof(*seed) + size); } else { pr_err("Could not map UEFI random seed!\n");-- 2.38.1