linux-kernel - [PATCH] efi: READ_ONCE rng seed size before munmap

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Message-Id: <20200217123354.21140-1-Jason@zx2c4.com>
Date:   Mon, 17 Feb 2020 13:33:54 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     ardb@...nel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>, stable@...r.kernel.org
Subject: [PATCH] efi: READ_ONCE rng seed size before munmap

This function is consistent with using size instead of seed->size
(except for one place that this patch fixes), but it reads seed->size
without using READ_ONCE, which means the compiler might still do
something unwanted. So, this commit simply adds the READ_ONCE
wrapper.

Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Cc: Ard Biesheuvel <ardb@...nel.org>
Cc: stable@...r.kernel.org
---
 drivers/firmware/efi/efi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 621220ab3d0e..21ea99f65113 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -552,7 +552,7 @@ 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 = seed->size;
+			size = READ_ONCE(seed->size);
 			early_memunmap(seed, sizeof(*seed));
 		} else {
 			pr_err("Could not map UEFI random seed!\n");
@@ -562,7 +562,7 @@ int __init efi_config_parse_tables(void *config_tables, int count, int sz,
 					      sizeof(*seed) + size);
 			if (seed != NULL) {
 				pr_notice("seeding entropy pool\n");
-				add_bootloader_randomness(seed->bits, seed->size);
+				add_bootloader_randomness(seed->bits, size);
 				early_memunmap(seed, sizeof(*seed) + size);
 			} else {
 				pr_err("Could not map UEFI random seed!\n");
-- 
2.25.0