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: stable@xxxxxxxxxxxxxxx > Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx> 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 > dri-devel@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/dri-devel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
