Commit ac47961e authored Oct 20, 2022 by Ard Biesheuvel Committed by Lipeng Sang May 24, 2023

efi: random: reduce seed size to 32 bytes

stable inclusion
from stable-v5.10.154
commit 83294f7c7759e1e4c3909edc2e2c1dfbb159e153
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I64YCB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=83294f7c7759e1e4c3909edc2e2c1dfbb159e153



--------------------------------

commit 161a438d upstream.

We no longer need at least 64 bytes of random seed to permit the early
crng init to complete. The RNG is now based on Blake2s, so reduce the
EFI seed size to the Blake2s hash size, which is sufficient for our
purposes.

While at it, drop the READ_ONCE(), which was supposed to prevent size
from being evaluated after seed was unmapped. However, this cannot
actually happen, so READ_ONCE() is unnecessary here.

Cc: <stable@vger.kernel.org> # v4.14+
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Lipeng Sang <sanglipeng1@jd.com>

parent 5b8dab0c

drivers/firmware/efi/efi.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -616,7 +616,7 @@ 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 = READ_ONCE(seed->size);
		size = min(seed->size, EFI_RANDOM_SEED_SIZE);
		early_memunmap(seed, sizeof(*seed));
		} else {
		pr_err("Could not map UEFI random seed!\n");

include/linux/efi.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -1180,7 +1180,7 @@ void efi_retrieve_tpm2_eventlog(void);
		arch_efi_call_virt_teardown(); \
		})

		#define EFI_RANDOM_SEED_SIZE 64U
		#define EFI_RANDOM_SEED_SIZE 32U // BLAKE2S_HASH_SIZE

		struct linux_efi_random_seed {
		u32 size;