Re: [PATCH v2 1/2] accel/amdxdna: clear the mailbox channel pointer when starting it fails

[Lizhi Hou <lizhi.hou@amd.com>]

Applied to drm-misc-next

On 9/15/26 09:36, Lizhi Hou wrote:
>
> On 9/13/26 14:31, Eva Crystal wrote:
>> aie2_create_context() allocates a mailbox channel, starts it, and on a
>> failed start frees it again:
>>
>>     hwctx->priv->mbox_chann = xdna_mailbox_alloc_channel(ndev->mbox);
>>     ...
>>     ret = xdna_mailbox_start_channel(hwctx->priv->mbox_chann, ...);
>>     if (ret)
>>         goto free_channel;
>>     ...
>> free_channel:
>>     xdna_mailbox_free_channel(hwctx->priv->mbox_chann);
>>
>> hwctx->priv->mbox_chann keeps pointing at the freed channel. That
>> pointer is the driver's own test for whether a hardware context has a
>> usable channel: aie2_destroy_context() returns early on NULL,
>> aie2_sched_job_run() refuses to run a job on NULL, and the message
>> helpers return -ENODEV on NULL. A stale pointer passes all of them.
>>
>> It matters on the restart path. aie2_hwctx_restart() calls
>> aie2_create_context() again on a hardware context that is already live,
>> after aie2_hwctx_stop() has torn its channel down, and the context
>> survives a failure there: aie2_sched_job_timedout() discards the return
>> value entirely, and aie2_hwctx_resume() only propagates it. What is
>> left is a live hardware context holding a freed channel, and every
>> later user of it takes the non-NULL branch:
>>
>>    - the next job submitted reaches xdna_mailbox_send_msg() on the freed
>>      channel, via the !mbox_chann guard in aie2_sched_job_run(),
>>    - a second command timeout reaches aie2_hwctx_stop() ->
>>      aie2_destroy_context(),
>>    - closing the device reaches aie2_hwctx_fini() ->
>>      aie2_release_resource() -> xrs_release_resource() ->
>>      aie2_xrs_unload() -> aie2_destroy_context(),
>>
>> and aie2_destroy_context() then calls xdna_mailbox_stop_channel()
>> followed by xdna_mailbox_free_channel() on memory that was already
>> freed: a use-after-free, and a second free of the same channel.
>>
>> The AIE4 management channel already does this correctly -
>> aie4_mailbox_start() clears ndev->aie.mgmt_chann right after freeing
>> it. Do the same here.
>>
>> The create path itself is not affected: when aie2_xrs_load() fails,
>> xrs_allocate_resource() removes the solver node without calling
>> ->unload, and aie2_hwctx_init() frees hwctx->priv, so the stale pointer
>> never outlives the structure holding it.
>>
>> Starting a channel can fail today without this patch: the ring buffer
>> sizes firmware reports are rejected unless both are powers of two, and
>> request_irq() can fail.
>>
>> Fixes: d5b8b0347fa8 ("accel/amdxdna: Split mailbox channel create 
>> function")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Eva Crystal <0xiviel@gmail.com>
>> ---
>>   drivers/accel/amdxdna/aie2_message.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/accel/amdxdna/aie2_message.c 
>> b/drivers/accel/amdxdna/aie2_message.c
>> index b4c49259a1a2..f658760c3d48 100644
>> --- a/drivers/accel/amdxdna/aie2_message.c
>> +++ b/drivers/accel/amdxdna/aie2_message.c
>> @@ -277,6 +277,7 @@ int aie2_create_context(struct amdxdna_dev_hdl 
>> *ndev, struct amdxdna_hwctx *hwct
>>     free_channel:
>>       xdna_mailbox_free_channel(hwctx->priv->mbox_chann);
>> +    hwctx->priv->mbox_chann = NULL;
> Reviewed-by: Lizhi Hou <lizhi.hou@amd.com>
>>   del_ctx_req:
>>       aie2_destroy_context_req(ndev, hwctx->fw_ctx_id);
>>       return ret;