On Tue, Oct 21, 2025 at 04:45:25PM +0800, 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@oss.qualcomm.com
Tested on my Juno board with below steps:
1) Enable the first path: ETM2 -> ETR0 echo 1 > /sys/bus/coresight/devices/tmc_etr0/enable_sink echo 1 > /sys/bus/coresight/devices/etm2/enable_source
2) Enlarge buffer size from 1MiB to 4MiB cat /sys/bus/coresight/devices/tmc_etr0/buffer_size 0x100000 echo 0x400000 > /sys/bus/coresight/devices/tmc_etr0/buffer_size
3) Enable the second path: ETM0 -> ETR0 echo 1 > /sys/bus/coresight/devices/etm0/enable_source
4) Disable paths echo 0 > /sys/bus/coresight/devices/etm0/enable_source echo 0 > /sys/bus/coresight/devices/etm2/enable_source
Without this patch, the oops will be triggered when disable paths. I can confirm this patch does dismiss the issue.
Tested-by: Leo Yan leo.yan@arm.com
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@oss.qualc...
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@oss.qualc...
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,
Xiaoqi Zhuang xiaoqi.zhuang@oss.qualcomm.com