[PATCH AUTOSEL 4.20 002/304] drm/v3d: Fix a use-after-free race accessing the scheduler's fences.

Sasha Levin
2019-01-28T17:52:57Z

From: Eric Anholt <eric@anholt.net>

[ Upstream commit 34c2c4f632f232ed2fdb66d4e42cc72d322273fe ]

Once we push the job, the scheduler could run it and free it. So, if
we want to reference their fences, we need to grab them before then.
I haven't seen this happen in many days of conformance test runtime,
but let's still close the race.

Signed-off-by: Eric Anholt <eric@anholt.net>
Fixes: 57692c94dcbe ("drm/v3d: Introduce a new DRM driver for Broadcom V3D V3.x+")
Link: https://patchwork.freedesktop.org/patch/254119/
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/v3d/v3d_drv.h | 5 +++++
drivers/gpu/drm/v3d/v3d_gem.c | 8 ++++++--
2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/v3d/v3d_drv.h b/drivers/gpu/drm/v3d/v3d_drv.h
index e6fed696ad86..cbe5be0c47eb 100644
--- a/drivers/gpu/drm/v3d/v3d_drv.h
+++ b/drivers/gpu/drm/v3d/v3d_drv.h
@@ -198,6 +198,11 @@ struct v3d_exec_info {
*/
struct dma_fence *bin_done_fence;

+ /* Fence for when the scheduler considers the render to be
+ * done, for when the BOs reservations should be complete.
+ */
+ struct dma_fence *render_done_fence;
+
struct kref refcount;

/* This is the array of BOs that were looked up at the start of exec. */
diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/v3d_gem.c
index 70c54774400b..2814c72cb090 100644
--- a/drivers/gpu/drm/v3d/v3d_gem.c
+++ b/drivers/gpu/drm/v3d/v3d_gem.c
@@ -209,7 +209,7 @@ v3d_flush_caches(struct v3d_dev *v3d)
static void
v3d_attach_object_fences(struct v3d_exec_info *exec)
{
- struct dma_fence *out_fence = &exec->render.base.s_fence->finished;
+ struct dma_fence *out_fence = exec->render_done_fence;
struct v3d_bo *bo;
int i;

@@ -409,6 +409,7 @@ v3d_exec_cleanup(struct kref *ref)
dma_fence_put(exec->render.done_fence);

dma_fence_put(exec->bin_done_fence);
+ dma_fence_put(exec->render_done_fence);

for (i = 0; i < exec->bo_count; i++)
drm_gem_object_put_unlocked(&exec->bo[i]->base);
@@ -572,6 +573,9 @@ v3d_submit_cl_ioctl(struct drm_device *dev, void *data,
if (ret)
goto fail_unreserve;

+ exec->render_done_fence =
+ dma_fence_get(&exec->render.base.s_fence->finished);
+
kref_get(&exec->refcount); /* put by scheduler job completion */
drm_sched_entity_push_job(&exec->render.base,
&v3d_priv->sched_entity[V3D_RENDER]);
@@ -585,7 +589,7 @@ v3d_submit_cl_ioctl(struct drm_device *dev, void *data,
sync_out = drm_syncobj_find(file_priv, args->out_sync);
if (sync_out) {
drm_syncobj_replace_fence(sync_out, 0,
- &exec->render.base.s_fence->finished);
+ exec->render_done_fence);
drm_syncobj_put(sync_out);
}

--
2.19.1