From fee896d4534fddff9476c95e6f244b70f5772ec1 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Thu, 20 Oct 2022 10:39:08 +0200 Subject: [PATCH] efi: random: reduce seed size to 32 bytes 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: # v4.14+ Signed-off-by: Ard Biesheuvel Reviewed-by: Jason A. Donenfeld Acked-by: Ilias Apalodimas Signed-off-by: Greg Kroah-Hartman --- drivers/firmware/efi/efi.c | 2 +- include/linux/efi.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c index 8fd74a7501d4..ac9fb336c80f 100644 --- a/drivers/firmware/efi/efi.c +++ b/drivers/firmware/efi/efi.c @@ -546,7 +546,7 @@ int __init efi_config_parse_tables(void *config_tables, int count, int sz, 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"); diff --git a/include/linux/efi.h b/include/linux/efi.h index f9b9f9a2fd4a..880cd86c829d 100644 --- a/include/linux/efi.h +++ b/include/linux/efi.h @@ -1715,7 +1715,7 @@ efi_status_t efi_exit_boot_services(efi_system_table_t *sys_table, 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;