Commit 7f3ebea1 authored Dec 19, 2018 by Gustavo A. R. Silva Committed by Greg Kroah-Hartman Dec 29, 2018

drm/ioctl: Fix Spectre v1 vulnerabilities

commit 505b5240329b922f21f91d5b5d1e535c805eca6d upstream.

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


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 6bb41321

drivers/gpu/drm/drm_ioctl.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -37,6 +37,7 @@

		#include <linux/pci.h>
		#include <linux/export.h>
		#include <linux/nospec.h>

		/**
		* DOC: getunique and setversion story
		@@ -794,13 +795,17 @@ 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];
		}

		@@ -882,6 +887,7 @@ 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;