linux-kernel - [PATCH 01/11] media: tm6000: fix potential Spectre variant 1

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Date:   Mon, 23 Apr 2018 12:38:03 -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>
Subject: [PATCH 01/11] media: tm6000: fix potential Spectre variant 1

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

Smatch warning:
drivers/media/usb/tm6000/tm6000-video.c:879 vidioc_enum_fmt_vid_cap() warn: potential spectre issue 'format'

Fix this by sanitizing f->index before using it to index
array _format_

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/usb/tm6000/tm6000-video.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/media/usb/tm6000/tm6000-video.c b/drivers/media/usb/tm6000/tm6000-video.c
index b2399d4..d701027 100644
--- a/drivers/media/usb/tm6000/tm6000-video.c
+++ b/drivers/media/usb/tm6000/tm6000-video.c
@@ -26,6 +26,7 @@
 #include <linux/kthread.h>
 #include <linux/highmem.h>
 #include <linux/freezer.h>
+#include <linux/nospec.h>
 
 #include "tm6000-regs.h"
 #include "tm6000.h"
@@ -875,6 +876,7 @@ static int vidioc_enum_fmt_vid_cap(struct file *file, void  *priv,
 	if (f->index >= ARRAY_SIZE(format))
 		return -EINVAL;
 
+	f->index = array_index_nospec(f->index, ARRAY_SIZE(format));
 	strlcpy(f->description, format[f->index].name, sizeof(f->description));
 	f->pixelformat = format[f->index].fourcc;
 	return 0;
-- 
2.7.4