From: Ard Biesheuvel ardb@kernel.org
commit 161a438d730dade2ba2b1bf8785f0759aba4ca5f 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 --- drivers/firmware/efi/efi.c | 2 +- include/linux/efi.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
--- a/drivers/firmware/efi/efi.c +++ b/drivers/firmware/efi/efi.c @@ -546,7 +546,7 @@ int __init efi_config_parse_tables(void
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"); --- a/include/linux/efi.h +++ b/include/linux/efi.h @@ -1715,7 +1715,7 @@ efi_status_t efi_exit_boot_services(efi_ void *priv, efi_exit_boot_map_processing priv_func);
-#define EFI_RANDOM_SEED_SIZE 64U +#define EFI_RANDOM_SEED_SIZE 32U // BLAKE2S_HASH_SIZE
struct linux_efi_random_seed { u32 size;