| Message ID | d7a2dd53d88360b12e5a14933cb931198760dd63.1602074787.git.saiprakash.ranjan@codeaurora.org |
|---|---|
| State | Accepted |
| Commit | 868663dd5d69fef05bfb004f91da5c30e9b93461 |
| Headers | show |
| Series | coresight: etf/etb: NULL Pointer dereference crash fixes | expand |
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 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 ? */ Suzuki
diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h index 65a29293b6cb..f5f654ea2994 100644 --- a/drivers/hwtracing/coresight/coresight-priv.h +++ b/drivers/hwtracing/coresight/coresight-priv.h @@ -87,6 +87,7 @@ enum cs_mode { * struct cs_buffer - keep track of a recording session' specifics * @cur: index of the current buffer * @nr_pages: max number of pages granted to us + * @pid: PID this cs_buffer belongs to * @offset: offset within the current buffer * @data_size: how much we collected in this run * @snapshot: is this run in snapshot mode @@ -95,6 +96,7 @@ enum cs_mode { struct cs_buffers { unsigned int cur; unsigned int nr_pages; + pid_t pid; unsigned long offset; local_t data_size; bool snapshot; diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c index 44402d413ebb..989d965f3d90 100644 --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c @@ -227,6 +227,7 @@ static int tmc_enable_etf_sink_perf(struct coresight_device *csdev, void *data) unsigned long flags; struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent); struct perf_output_handle *handle = data; + struct cs_buffers *buf = etm_perf_sink_config(handle); spin_lock_irqsave(&drvdata->spinlock, flags); do { @@ -243,7 +244,7 @@ static int tmc_enable_etf_sink_perf(struct coresight_device *csdev, void *data) } /* Get a handle on the pid of the process to monitor */ - pid = task_pid_nr(handle->event->owner); + pid = buf->pid; if (drvdata->pid != -1 && drvdata->pid != pid) { ret = -EBUSY; @@ -399,6 +400,7 @@ static void *tmc_alloc_etf_buffer(struct coresight_device *csdev, if (!buf) return NULL; + buf->pid = task_pid_nr(event->owner); buf->snapshot = overwrite; buf->nr_pages = nr_pages; buf->data_pages = pages;
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 same thing with ETF and cache the PID to which the cs_buffer belongs in tmc_alloc_etf_buffer() as done for ETR. This will also remove the unnecessary function calls(task_pid_nr()) since we are caching the PID. Easily reproducible running below: perf record -e cs_etm/@tmc_etf0/ -N -p <pid> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000548 Mem abort info: ESR = 0x96000006 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 Data abort info: ISV = 0, ISS = 0x00000006 CM = 0, WnR = 0 <snip>... Call trace: tmc_enable_etf_sink+0xe4/0x280 coresight_enable_path+0x168/0x1fc etm_event_start+0x8c/0xf8 etm_event_add+0x38/0x54 event_sched_in+0x194/0x2ac group_sched_in+0x54/0x12c flexible_sched_in+0xd8/0x120 visit_groups_merge+0x100/0x16c ctx_flexible_sched_in+0x50/0x74 ctx_sched_in+0xa4/0xa8 perf_event_sched_in+0x60/0x6c perf_event_context_sched_in+0x98/0xe0 __perf_event_task_sched_in+0x5c/0xd8 finish_task_switch+0x184/0x1cc schedule_tail+0x20/0xec ret_from_fork+0x4/0x18 Fixes: 880af782c6e8 ("coresight: tmc-etf: Add support for CPU-wide trace scenarios") Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org> --- drivers/hwtracing/coresight/coresight-priv.h | 2 ++ drivers/hwtracing/coresight/coresight-tmc-etf.c | 4 +++- 2 files changed, 5 insertions(+), 1 deletion(-)