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

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

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;