linux-kernel - [PATCH 09/11] vimc-debayer: fix potential Spectre variant 1

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Date:   Mon, 23 Apr 2018 12:50:07 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Helen Koike <helen.koike@...labora.com>
Subject: [PATCH 09/11] vimc-debayer: fix potential Spectre variant 1

code->index can be controlled by user-space, hence leading to
a potential exploitation of the Spectre variant 1 vulnerability.

Smatch warning:
drivers/media/platform/vimc/vimc-debayer.c:182 vimc_deb_enum_mbus_code() warn: potential spectre issue 'vimc_deb_pix_map_list'

Fix this by sanitizing code->index before using it to index
vimc_deb_pix_map_list.

Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

Cc: stable@...r.kernel.org
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
 drivers/media/platform/vimc/vimc-debayer.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/media/platform/vimc/vimc-debayer.c b/drivers/media/platform/vimc/vimc-debayer.c
index 6e10b63..bdd96bb 100644
--- a/drivers/media/platform/vimc/vimc-debayer.c
+++ b/drivers/media/platform/vimc/vimc-debayer.c
@@ -24,6 +24,8 @@
 
 #include "vimc-common.h"
 
+#include <linux/nospec.h>
+
 #define VIMC_DEB_DRV_NAME "vimc-debayer"
 
 static unsigned int deb_mean_win_size = 3;
@@ -178,7 +180,8 @@ static int vimc_deb_enum_mbus_code(struct v4l2_subdev *sd,
 	} else {
 		if (code->index >= ARRAY_SIZE(vimc_deb_pix_map_list))
 			return -EINVAL;
-
+		code->index = array_index_nospec(code->index,
+					    ARRAY_SIZE(vimc_deb_pix_map_list));
 		code->code = vimc_deb_pix_map_list[code->index].code;
 	}
 
-- 
2.7.4