Re: [PATCH] cxl/mbox: Break poison list loop on an empty payload

[Dave Jiang <dave.jiang@intel.com>]

On 7/9/26 8:57 AM, Dave Jiang wrote:
> A device that returns count == 0 with CXL_POISON_FLAG_MORE set on every
> iteration never advances nr_records, so the max_errors guard never
> trips and the do/while loops forever while holding poison.mutex. That
> hangs the sysfs-triggered scan thread and blocks all subsequent poison
> operations on the device. The existing "Protect against an uncleared
> _FLAG_MORE" guard was intended to bound a misbehaving device but does
> not cover the count == 0 case.
> 
> Stop the loop on an empty payload so a malfunctioning or malicious
> device cannot wedge the poison scan.
> 
> Link: https://sashiko.dev/#/patchset/20260702090849.47501-1-icheng@nvidia.com?part=3
> Fixes: ed83f7ca398b ("cxl/mbox: Add GET_POISON_LIST mailbox command")
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>

Applied to cxl/next
8b301c4afbce


> ---
>  drivers/cxl/core/mbox.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
> index 7c6c5b7450a5..c09fae2cae9f 100644
> --- a/drivers/cxl/core/mbox.c
> +++ b/drivers/cxl/core/mbox.c
> @@ -1455,6 +1455,11 @@ int cxl_mem_get_poison(struct cxl_memdev *cxlmd, u64 offset, u64 len,
>  		if (rc)
>  			break;
>  
> +		if (!le16_to_cpu(po->count)) {
> +			dev_dbg(&cxlmd->dev, "Poison empty payload!\n");
> +			break;
> +		}
> +
>  		for (int i = 0; i < le16_to_cpu(po->count); i++)
>  			trace_cxl_poison(cxlmd, cxlr, &po->record[i],
>  					 po->flags, po->overflow_ts,
> 
> base-commit: 8cdeaa50eae8dad34885515f62559ee83e7e8dda