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drm/ioctl: Fix Spectre v1 vulnerabilities 

nr is 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_ioctl.c:805 drm_ioctl() warn: potential spectre issue 'dev->driver->ioctls' [r]
drivers/gpu/drm/drm_ioctl.c:810 drm_ioctl() warn: potential spectre issue 'drm_ioctls' [r] (local cap)
drivers/gpu/drm/drm_ioctl.c:892 drm_ioctl_flags() warn: potential spectre issue 'drm_ioctls' [r] (local cap)

Fix this by sanitizing nr before using it to index dev->driver->ioctls
and drm_ioctls.

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
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/20181220000015.GA18973@embeddedor
This commit is contained in:
Gustavo A. R. Silva 2018-12-19 18:00:15 -06:00 committed by Daniel Vetter
parent 7566ec393f
commit 505b524032
1 changed files with 8 additions and 2 deletions
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10
drivers/gpu/drm/drm_ioctl.c
View File

@ -37,6 +37,7 @@
#include <linux/pci.h>
#include <linux/export.h>
#include <linux/nospec.h>
/**
* DOC: getunique and setversion story
@ -800,13 +801,17 @@ long drm_ioctl(struct file *filp,
if (is_driver_ioctl) {
/* driver ioctl */
if (nr - DRM_COMMAND_BASE >= dev->driver->num_ioctls)
unsigned int index = nr - DRM_COMMAND_BASE;
if (index >= dev->driver->num_ioctls)
goto err_i1;
ioctl = &dev->driver->ioctls[nr - DRM_COMMAND_BASE];
index = array_index_nospec(index, dev->driver->num_ioctls);
ioctl = &dev->driver->ioctls[index];
} else {
/* core ioctl */
if (nr >= DRM_CORE_IOCTL_COUNT)
goto err_i1;
nr = array_index_nospec(nr, DRM_CORE_IOCTL_COUNT);
ioctl = &drm_ioctls[nr];
}
@ -888,6 +893,7 @@ bool drm_ioctl_flags(unsigned int nr, unsigned int *flags)
if (nr >= DRM_CORE_IOCTL_COUNT)
return false;
nr = array_index_nospec(nr, DRM_CORE_IOCTL_COUNT);
*flags = drm_ioctls[nr].flags;
return true;