Messages in this thread Patch in this message | | | Date | Wed, 14 Oct 2020 13:20:05 +0530 | From | Sai Prakash Ranjan <> | Subject | Re: [PATCH 1/2] coresight: tmc-etf: Fix NULL ptr dereference in tmc_enable_etf_sink_perf() |
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Hi Suzuki,
On 2020-10-13 22:05, Suzuki K Poulose wrote: > On 10/07/2020 02:00 PM, Sai Prakash Ranjan wrote: >> There was a report of NULL pointer dereference in ETF enable >> path for perf CS mode with PID monitoring. It is almost 100% >> reproducible when the process to monitor is something very >> active such as chrome and with ETF as the sink and not ETR. >> Currently in a bid to find the pid, the owner is dereferenced >> via task_pid_nr() call in tmc_enable_etf_sink_perf() and with >> owner being NULL, we get a NULL pointer dereference. >> >> Looking at the ETR and other places in the kernel, ETF and the >> ETB are the only places trying to dereference the task(owner) >> in tmc_enable_etf_sink_perf() which is also called from the >> sched_in path as in the call trace. Owner(task) is NULL even >> in the case of ETR in tmc_enable_etr_sink_perf(), but since we >> cache the PID in alloc_buffer() callback and it is done as part >> of etm_setup_aux() when allocating buffer for ETR sink, we never >> dereference this NULL pointer and we are safe. So lets do the > > The patch is necessary to fix some of the issues. But I feel it is > not complete. Why is it safe earlier and not later ? I believe we are > simply reducing the chances of hitting the issue, by doing this earlier > than > later.
I did stress it for a long time with this patch and did not face any issues but I guess it doesn't hurt to have the check as you suggested.
> I would say we better fix all instances to make sure that the > event->owner is valid. (e.g, I can see that the for kernel events > event->owner == -1 ?) > > struct task_struct *tsk = READ_ONCE(event->owner); > > if (!tsk || is_kernel_event(event)) > /* skip ? */ >
So to confirm my understanding, I will add the above checks on top of this patch for ETR, ETB and ETF something like below?
diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c index 989d965f3d90..86ff0dda0444 100644 --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c @@ -392,6 +392,10 @@ static void *tmc_alloc_etf_buffer(struct coresight_device *csdev, { int node; struct cs_buffers *buf; + struct task_struct *task = READ_ONCE(event->owner); + + if (!task || is_kernel_event(event)) + return NULL;
node = (event->cpu == -1) ? NUMA_NO_NODE : cpu_to_node(event->cpu);
@@ -400,7 +404,7 @@ static void *tmc_alloc_etf_buffer(struct coresight_device *csdev, if (!buf) return NULL;
- buf->pid = task_pid_nr(event->owner); + buf->pid = task_pid_nr(task); buf->snapshot = overwrite; buf->nr_pages = nr_pages; buf->data_pages = pages;
Thanks, Sai -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation
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