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drm/bufs: Fix Spectre v1 vulnerability

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

This issue was detected with the help of Smatch:

drivers/gpu/drm/drm_bufs.c:1420 drm_legacy_freebufs() warn: potential
spectre issue 'dma->buflist' [r] (local cap)

Fix this by sanitizing idx before using it to index dma->buflist

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

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20181016095549.GA23586@embeddedor.com
This commit is contained in:
Gustavo A. R. Silva 2018-10-16 11:55:49 +02:00 committed by Daniel Vetter
parent 871edc96bd
commit a378050989
1 changed files with 3 additions and 0 deletions
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3
drivers/gpu/drm/drm_bufs.c
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@ -36,6 +36,8 @@
#include <drm/drmP.h>
#include "drm_legacy.h"
#include <linux/nospec.h>
static struct drm_map_list *drm_find_matching_map(struct drm_device *dev,
struct drm_local_map *map)
{
@ -1417,6 +1419,7 @@ int drm_legacy_freebufs(struct drm_device *dev, void *data,
idx, dma->buf_count - 1);
return -EINVAL;
}
idx = array_index_nospec(idx, dma->buf_count);
buf = dma->buflist[idx];
if (buf->file_priv != file_priv) {
DRM_ERROR("Process %d freeing buffer not owned\n",