Re: [PATCH] drm/amdkfd: fix potential kgd_mem UAFs

[Felix Kuehling]

Am 2023-03-08 um 16:37 schrieb Chia-I Wu:
> kgd_mem should be accessed with p->mutex locked, or it could have been
> freed by kfd_ioctl_free_memory_of_gpu.

Thank you for the patch. It's not just about accessing kgd_mem with 
p->mutex held. It's also about holding the mutex continuously. I'd 
update the description to be more explicit about the invariant being 
broken here:

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.

I can update the description and submit the patch.

Reviewed-by: Felix Kuehling <Felix.Kuehling@xxxxxxx>

Regards,
  Felix


> Signed-off-by: Chia-I Wu <olvaffe@xxxxxxxxx>
> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_chardev.c | 16 ++++++++++------
>   1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c b/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
> index 6d291aa6386bd..3c630114210d6 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_chardev.c
> @@ -1293,14 +1293,14 @@ 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]);
> @@ -1316,9 +1316,9 @@ 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;
> @@ -1332,6 +1332,7 @@ 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");
> @@ -1384,16 +1385,19 @@ 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]);
> @@ -1409,9 +1413,9 @@ 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;
>   }