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
Cc: [email protected]
Signed-off-by: Gustavo A. R. Silva <[email protected]>
---
drivers/gpu/drm/drm_bufs.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/gpu/drm/drm_bufs.c b/drivers/gpu/drm/drm_bufs.c
index 7412aca..d7d10ca 100644
--- a/drivers/gpu/drm/drm_bufs.c
+++ b/drivers/gpu/drm/drm_bufs.c
@@ -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",
--
2.7.4
On Tue, Oct 16, 2018 at 11:55:49AM +0200, Gustavo A. R. Silva wrote:
> 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
>
> Cc: [email protected]
> Signed-off-by: Gustavo A. R. Silva <[email protected]>
Applied since it's correct, but I dropped the cc: stable. This code is
very dead and full of security issues, and spectre is the least of your
worries. If you want to a stab at fixing the real spectre issues in drm,
then look anywhere that isn't full of drm_legacy_* functions.
The most important file is probably drm_ioctl.c.
-Daniel
> ---
> drivers/gpu/drm/drm_bufs.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_bufs.c b/drivers/gpu/drm/drm_bufs.c
> index 7412aca..d7d10ca 100644
> --- a/drivers/gpu/drm/drm_bufs.c
> +++ b/drivers/gpu/drm/drm_bufs.c
> @@ -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",
> --
> 2.7.4
>
> _______________________________________________
> dri-devel mailing list
> [email protected]
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
On 10/17/18 9:19 AM, Daniel Vetter wrote:
>> Cc: [email protected]
>> Signed-off-by: Gustavo A. R. Silva <[email protected]>
>
> Applied since it's correct, but I dropped the cc: stable. This code is
> very dead and full of security issues, and spectre is the least of your
> worries. If you want to a stab at fixing the real spectre issues in drm,
> then look anywhere that isn't full of drm_legacy_* functions.
>
OK. I've got it.
> The most important file is probably drm_ioctl.c.
> -Daniel
>
Thanks for the feedback, Daniel.
--
Gustavo