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[03/11] fsl-viu: fix potential Spectre variant 1

Message ID a9c766d2aaf75b568ae1cf177c62e90e4eea67f3.1524499368.git.gustavo@embeddedor.com (mailing list archive)
State New, archived
Headers show

Commit Message

Gustavo A. R. Silva April 23, 2018, 5:39 p.m. UTC 
f->index can be controlled by user-space, hence leading to a
potential exploitation of the Spectre variant 1 vulnerability.

Smatch warning:
drivers/media/platform/fsl-viu.c:587 vidioc_enum_fmt() warn: potential spectre issue 'formats'

Fix this by sanitizing f->index before using it to index
formats.

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@vger.kernel.org
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 drivers/media/platform/fsl-viu.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
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Patch

diff --git a/drivers/media/platform/fsl-viu.c b/drivers/media/platform/fsl-viu.c
index e41510c..8356d26 100644
--- a/drivers/media/platform/fsl-viu.c
+++ b/drivers/media/platform/fsl-viu.c
@@ -33,6 +33,8 @@ 
 #include <media/v4l2-event.h>
 #include <media/videobuf-dma-contig.h>
 
+#include <linux/nospec.h>
+
 #define DRV_NAME		"fsl_viu"
 #define VIU_VERSION		"0.5.1"
 
@@ -579,12 +581,10 @@  static int vidioc_querycap(struct file *file, void *priv,
 static int vidioc_enum_fmt(struct file *file, void  *priv,
 					struct v4l2_fmtdesc *f)
 {
-	int index = f->index;
-
 	if (f->index >= NUM_FORMATS)
 		return -EINVAL;
-
-	f->pixelformat = formats[index].fourcc;
+	f->index = array_index_nospec(f->index, NUM_FORMATS);
+	f->pixelformat = formats[f->index].fourcc;
 	return 0;
 }