This is a note to let you know that I've just added the patch titled
efi: random: reduce seed size to 32 bytes
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
efi-random-reduce-seed-size-to-32-bytes.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 161a438d730dade2ba2b1bf8785f0759aba4ca5f Mon Sep 17 00:00:00 2001
From: Ard Biesheuvel <ardb@xxxxxxxxxx>
Date: Thu, 20 Oct 2022 10:39:08 +0200
Subject: efi: random: reduce seed size to 32 bytes
From: Ard Biesheuvel <ardb@xxxxxxxxxx>
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@xxxxxxxxxxxxxxx> # v4.14+
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Reviewed-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Acked-by: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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;
Patches currently in stable-queue which might be from ardb@xxxxxxxxxx are
queue-5.4/efi-random-reduce-seed-size-to-32-bytes.patch
