drm/panfrost: Job should reference MMU not file_priv

For a while now it's been allowed for a MMU context to outlive it's
corresponding panfrost_priv, however the job structure still references
panfrost_priv to get hold of the MMU context. If panfrost_priv has been
freed this is a use-after-free which I've been able to trigger resulting
in a splat.

To fix this, drop the reference to panfrost_priv in the job structure
and add a direct reference to the MMU structure which is what's actually
needed.

Fixes: 7fdc48cc ("drm/panfrost: Make sure MMU context lifetime is not bound to panfrost_priv")
Signed-off-by: Steven Price <steven.price@arm.com>
Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220519152003.81081-1-steven.price@arm.com

drivers/gpu/drm/panfrost/panfrost_drv.c

@@ -233,6 +233,7 @@ static int panfrost_ioctl_submit(struct drm_device *dev, void *data,
 		struct drm_file *file)
 {
 	struct panfrost_device *pfdev = dev->dev_private;
+	struct panfrost_file_priv *file_priv = file->driver_priv;
 	struct drm_panfrost_submit *args = data;
 	struct drm_syncobj *sync_out = NULL;
 	struct panfrost_job *job;
@@ -262,12 +263,12 @@ static int panfrost_ioctl_submit(struct drm_device *dev, void *data,
 	job->jc = args->jc;
 	job->requirements = args->requirements;
 	job->flush_id = panfrost_gpu_get_latest_flush_id(pfdev);
-	job->file_priv = file->driver_priv;
+	job->mmu = file_priv->mmu;
 
 	slot = panfrost_job_get_slot(job);
 
 	ret = drm_sched_job_init(&job->base,
-				 &job->file_priv->sched_entity[slot],
+				 &file_priv->sched_entity[slot],
 				 NULL);
 	if (ret)
 		goto out_put_job;

drivers/gpu/drm/panfrost/panfrost_job.c

@@ -201,7 +201,7 @@ static void panfrost_job_hw_submit(struct panfrost_job *job, int js)
 		return;
 	}
 
-	cfg = panfrost_mmu_as_get(pfdev, job->file_priv->mmu);
+	cfg = panfrost_mmu_as_get(pfdev, job->mmu);
 
 	job_write(pfdev, JS_HEAD_NEXT_LO(js), lower_32_bits(jc_head));
 	job_write(pfdev, JS_HEAD_NEXT_HI(js), upper_32_bits(jc_head));
@@ -431,7 +431,7 @@ static void panfrost_job_handle_err(struct panfrost_device *pfdev,
 		job->jc = 0;
 	}
 
-	panfrost_mmu_as_put(pfdev, job->file_priv->mmu);
+	panfrost_mmu_as_put(pfdev, job->mmu);
 	panfrost_devfreq_record_idle(&pfdev->pfdevfreq);
 
 	if (signal_fence)
@@ -452,7 +452,7 @@ static void panfrost_job_handle_done(struct panfrost_device *pfdev,
 	 * happen when we receive the DONE interrupt while doing a GPU reset).
 	 */
 	job->jc = 0;
-	panfrost_mmu_as_put(pfdev, job->file_priv->mmu);
+	panfrost_mmu_as_put(pfdev, job->mmu);
 	panfrost_devfreq_record_idle(&pfdev->pfdevfreq);
 
 	dma_fence_signal_locked(job->done_fence);

drivers/gpu/drm/panfrost/panfrost_job.h

@@ -17,7 +17,7 @@ struct panfrost_job {
 	struct kref refcount;
 
 	struct panfrost_device *pfdev;
-	struct panfrost_file_priv *file_priv;
+	struct panfrost_mmu *mmu;
 
 	/* Fence to be signaled by IRQ handler when the job is complete. */
 	struct dma_fence *done_fence;