Re: [PATCH v3] coresight: ETR: Fix ETR buffer use-after-free issue

[Xiaoqi Zhuang]

On 10/21/2025 16:45, Xiaoqi Zhuang wrote:
> When ETR is enabled as CS_MODE_SYSFS, if the buffer size is changed
> and enabled again, currently sysfs_buf will point to the newly
> allocated memory(buf_new) and free the old memory(buf_old). But the
> etr_buf that is being used by the ETR remains pointed to buf_old, not
> updated to buf_new. In this case, it will result in a memory
> use-after-free issue.
>
> Fix this by checking ETR's mode before updating and releasing buf_old,
> if the mode is CS_MODE_SYSFS, then skip updating and releasing it.
>
> Fixes: bd2767ec3df2 ("coresight: Fix run time warnings while reusing ETR buffer")
> Signed-off-by: Xiaoqi Zhuang <xiaoqi.zhuang@xxxxxxxxxxxxxxxx>
> ---
> Changes in v3:
> - Add a fix tag for the fix patch.
> - Link to v2: https://lore.kernel.org/r/20251021-fix_etr_issue-v2-1-80c40c9cac8c@xxxxxxxxxxxxxxxx
>
> Changes in v2:
> - Exit earlier to avoid allocating memory unnecessarily.
> - Link to v1: https://lore.kernel.org/r/20251020-fix_etr_issue-v1-1-902ab51770b4@xxxxxxxxxxxxxxxx
> ---
>   drivers/hwtracing/coresight/coresight-tmc-etr.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> index b07fcdb3fe1a..800be06598c1 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> @@ -1250,6 +1250,13 @@ static struct etr_buf *tmc_etr_get_sysfs_buffer(struct coresight_device *csdev)
>   	 * with the lock released.
>   	 */
>   	raw_spin_lock_irqsave(&drvdata->spinlock, flags);
> +
> +	/*
> +	 * If the ETR is already enabled, continue with the existing buffer.
> +	 */
> +	if (coresight_get_mode(csdev) == CS_MODE_SYSFS)
> +		goto out;
> +
>   	sysfs_buf = READ_ONCE(drvdata->sysfs_buf);
>   	if (!sysfs_buf || (sysfs_buf->size != drvdata->size)) {
>   		raw_spin_unlock_irqrestore(&drvdata->spinlock, flags);
>
> ---
> base-commit: 98ac9cc4b4452ed7e714eddc8c90ac4ae5da1a09
> change-id: 20251020-fix_etr_issue-02c706dbc899
>
> Best regards,


Gentle reminder.

--
Thanks and Regards,
Xiaoqi