drm/amdkfd: fix potential kgd_mem UAFs

kgd_mem pointers returned by kfd_process_device_translate_handle are
only guaranteed to be valid while p->mutex is held. As soon as the mutex
is unlocked, another thread can free the BO.
Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdkfd/kfd_chardev.c

@@ -1312,14 +1312,14 @@ static int kfd_ioctl_map_memory_to_gpu(struct file *filep,
 		args->n_success = i+1;
 	}
 
-	mutex_unlock(&p->mutex);
-
 	err = amdgpu_amdkfd_gpuvm_sync_memory(dev->adev, (struct kgd_mem *) mem, true);
 	if (err) {
 		pr_debug("Sync memory failed, wait interrupted by user signal\n");
 		goto sync_memory_failed;
 	}
 
+	mutex_unlock(&p->mutex);
+
 	/* Flush TLBs after waiting for the page table updates to complete */
 	for (i = 0; i < args->n_devices; i++) {
 		peer_pdd = kfd_process_device_data_by_id(p, devices_arr[i]);
@@ -1335,9 +1335,9 @@ static int kfd_ioctl_map_memory_to_gpu(struct file *filep,
 bind_process_to_device_failed:
 get_mem_obj_from_handle_failed:
 map_memory_to_gpu_failed:
+sync_memory_failed:
 	mutex_unlock(&p->mutex);
 copy_from_user_failed:
-sync_memory_failed:
 	kfree(devices_arr);
 
 	return err;
@@ -1351,6 +1351,7 @@ static int kfd_ioctl_unmap_memory_from_gpu(struct file *filep,
 	void *mem;
 	long err = 0;
 	uint32_t *devices_arr = NULL, i;
+	bool flush_tlb;
 
 	if (!args->n_devices) {
 		pr_debug("Device IDs array empty\n");
@@ -1403,16 +1404,19 @@ static int kfd_ioctl_unmap_memory_from_gpu(struct file *filep,
 		}
 		args->n_success = i+1;
 	}
-	mutex_unlock(&p->mutex);
 
-	if (kfd_flush_tlb_after_unmap(pdd->dev)) {
+	flush_tlb = kfd_flush_tlb_after_unmap(pdd->dev);
+	if (flush_tlb) {
 		err = amdgpu_amdkfd_gpuvm_sync_memory(pdd->dev->adev,
 				(struct kgd_mem *) mem, true);
 		if (err) {
 			pr_debug("Sync memory failed, wait interrupted by user signal\n");
 			goto sync_memory_failed;
 		}
+	}
+	mutex_unlock(&p->mutex);
 
+	if (flush_tlb) {
 		/* Flush TLBs after waiting for the page table updates to complete */
 		for (i = 0; i < args->n_devices; i++) {
 			peer_pdd = kfd_process_device_data_by_id(p, devices_arr[i]);
@@ -1428,9 +1432,9 @@ static int kfd_ioctl_unmap_memory_from_gpu(struct file *filep,
 bind_process_to_device_failed:
 get_mem_obj_from_handle_failed:
 unmap_memory_from_gpu_failed:
+sync_memory_failed:
 	mutex_unlock(&p->mutex);
 copy_from_user_failed:
-sync_memory_failed:
 	kfree(devices_arr);
 	return err;
 }