[PATCH] drm/amdgpu: fix NULL dereference in gfx_v9_0_kcq() and kiq_init_queue()

[Alexey Nepomnyashih]

A potential NULL pointer dereference may occur when accessing 
tmp_mqd->cp_hqd_pq_control without verifying that tmp_mqd is non-NULL.
This may happen if mqd_backup[mqd_idx] is unexpectedly NULL.

Although a NULL check for mqd_backup[mqd_idx] existed previously, it was
moved to a position after the dereference in a recent commit, which
renders it ineffective.

Add an explicit NULL check for tmp_mqd before dereferencing its members.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Cc: stable at vger.kernel.org # v5.13+
Fixes: a330b52a9e59 ("drm/amdgpu: Init the cp MQD if it's not be initialized before")
Signed-off-by: Alexey Nepomnyashih <sdl at nppct.ru>
---
 drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c b/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
index d7db4cb907ae..134cab16a00d 100644
--- a/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
+++ b/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
@@ -3817,10 +3817,9 @@ static int gfx_v9_0_kiq_init_queue(struct amdgpu_ring *ring)
 	 * check mqd->cp_hqd_pq_control since this value should not be 0
 	 */
 	tmp_mqd = (struct v9_mqd *)adev->gfx.kiq[0].mqd_backup;
-	if (amdgpu_in_reset(adev) && tmp_mqd->cp_hqd_pq_control){
+	if (amdgpu_in_reset(adev) && tmp_mqd && tmp_mqd->cp_hqd_pq_control) {
 		/* for GPU_RESET case , reset MQD to a clean status */
-		if (adev->gfx.kiq[0].mqd_backup)
-			memcpy(mqd, adev->gfx.kiq[0].mqd_backup, sizeof(struct v9_mqd_allocation));
+		memcpy(mqd, adev->gfx.kiq[0].mqd_backup, sizeof(struct v9_mqd_allocation));
 
 		/* reset ring buffer */
 		ring->wptr = 0;
@@ -3863,7 +3862,7 @@ static int gfx_v9_0_kcq_init_queue(struct amdgpu_ring *ring, bool restore)
 	 */
 	tmp_mqd = (struct v9_mqd *)adev->gfx.mec.mqd_backup[mqd_idx];
 
-	if (!restore && (!tmp_mqd->cp_hqd_pq_control ||
+	if (!restore && tmp_mqd && (!tmp_mqd->cp_hqd_pq_control ||
 	    (!amdgpu_in_reset(adev) && !adev->in_suspend))) {
 		memset((void *)mqd, 0, sizeof(struct v9_mqd_allocation));
 		((struct v9_mqd_allocation *)mqd)->dynamic_cu_mask = 0xFFFFFFFF;
@@ -3874,8 +3873,7 @@ static int gfx_v9_0_kcq_init_queue(struct amdgpu_ring *ring, bool restore)
 		soc15_grbm_select(adev, 0, 0, 0, 0, 0);
 		mutex_unlock(&adev->srbm_mutex);
 
-		if (adev->gfx.mec.mqd_backup[mqd_idx])
-			memcpy(adev->gfx.mec.mqd_backup[mqd_idx], mqd, sizeof(struct v9_mqd_allocation));
+		memcpy(adev->gfx.mec.mqd_backup[mqd_idx], mqd, sizeof(struct v9_mqd_allocation));
 	} else {
 		/* restore MQD to a clean status */
 		if (adev->gfx.mec.mqd_backup[mqd_idx])
-- 
2.43.0