Re: [PATCH 1/3] platform/x86/amd: hfi: Fix a use-after-free when unloading the driver

[Mario Limonciello]

On 9/21/26 12:04, Mario Limonciello wrote:
> amd_hfi_probe() registers CPU hotplug callbacks with
> cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, ...) and schedules the static
> sched_amd_hfi_itmt_work work item, but amd_hfi_remove() tears down
> neither.  The dynamically assigned hotplug state returned by
> cpuhp_setup_state() is discarded, so cpuhp_remove_state() can never be
> called, and the pending work is never cancelled.
>
> After the module is unloaded and its memory is freed, any subsequent CPU
> hotplug event or execution of the scheduled work dereferences the stale
> callback and work function pointers, resulting in a use-after-free and
> kernel panic.
>
> Store the hotplug state returned by cpuhp_setup_state() and, on removal,
> call cpuhp_remove_state() to unregister the callbacks and
> cancel_work_sync() to flush the scheduled work before the module memory
> goes away.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: bb20421c05fc ("platform/x86: hfi: Add online and offline callback support")
> Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>

Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
Closes: 
https://sashiko.dev/#/bug/linux-e2a43433-2732-4af4-97f1-ec320a95f087> ---
>   drivers/platform/x86/amd/hfi/hfi.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/drivers/platform/x86/amd/hfi/hfi.c b/drivers/platform/x86/amd/hfi/hfi.c
> index e0ebcb0c4acde..e1c776b71f3e6 100644
> --- a/drivers/platform/x86/amd/hfi/hfi.c
> +++ b/drivers/platform/x86/amd/hfi/hfi.c
> @@ -76,6 +76,8 @@ struct amd_hfi_data {
>   	struct amd_shmem_info	*shmem;
>   
>   	struct dentry *dbgfs_dir;
> +
> +	int cpuhp_state;
>   };
>   
>   /**
> @@ -244,6 +246,8 @@ static void amd_hfi_remove(struct platform_device *pdev)
>   {
>   	struct amd_hfi_data *dev = platform_get_drvdata(pdev);
>   
> +	cpuhp_remove_state(dev->cpuhp_state);
> +	cancel_work_sync(&sched_amd_hfi_itmt_work);
>   	debugfs_remove_recursive(dev->dbgfs_dir);
>   }
>   
> @@ -494,6 +498,7 @@ static int amd_hfi_probe(struct platform_device *pdev)
>   				amd_hfi_online, amd_hfi_offline);
>   	if (ret < 0)
>   		return ret;
> +	amd_hfi_data->cpuhp_state = ret;
>   
>   	schedule_work(&sched_amd_hfi_itmt_work);
>