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From: Ard Biesheuvel <ardb@kernel.org>
To: linux-efi@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	linux-kernel@vger.kernel.org
Subject: [PATCH 4/4] efi: READ_ONCE rng seed size before munmap
Date: Fri, 21 Feb 2020 09:48:49 +0100
Message-ID: <20200221084849.26878-5-ardb@kernel.org> (raw)
In-Reply-To: <20200221084849.26878-1-ardb@kernel.org>

From: "Jason A. Donenfeld" <Jason@zx2c4.com>

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@zx2c4.com>
Fixes: 636259880a7e ("efi: Add support for seeding the RNG from a UEFI ...")
Link: https://lore.kernel.org/r/20200217123354.21140-1-Jason@zx2c4.com
Signed-off-by: Ard Biesheuvel <ardb@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");
-- 
2.17.1


      parent reply index

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-21  8:48 [GIT PULL 0/4] EFI fixes for v5.6-rc Ard Biesheuvel
2020-02-21  8:48 ` [PATCH 1/4] efi/x86: align GUIDs to their size in the mixed mode runtime wrapper Ard Biesheuvel
2020-02-26 16:55   ` [tip: efi/urgent] efi/x86: Align " tip-bot2 for Ard Biesheuvel
2020-02-21  8:48 ` [PATCH 2/4] efi/x86: remove support for EFI time and counter services in mixed mode Ard Biesheuvel
2020-02-26 16:55   ` [tip: efi/urgent] efi/x86: Remove " tip-bot2 for Ard Biesheuvel
2020-02-21  8:48 ` [PATCH 3/4] efi/x86: Handle by-ref arguments covering multiple pages " Ard Biesheuvel
2020-02-26 16:55   ` [tip: efi/urgent] " tip-bot2 for Ard Biesheuvel
2020-02-21  8:48 ` Ard Biesheuvel [this message]

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