Messages in this thread | | | Date | Thu, 22 Oct 2020 16:40:40 +0530 | From | Sai Prakash Ranjan <> | Subject | Re: [PATCHv2 0/4] coresight: etf/etb10/etr: Fix NULL pointer dereference crashes |
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On 2020-10-22 16:27, 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 > same thing with ETF and ETB and cache the PID to which the > cs_buffer belongs in alloc_buffer() callback for ETF and ETB as > done for ETR. This will also remove the unnecessary function calls > (task_pid_nr()) in tmc_enable_etr_sink_perf() and etb_enable_perf(). > > In addition to this, add a check to validate event->owner before > dereferencing it in ETR, ETB and ETF to avoid any possible NULL > pointer dereference crashes in their corresponding alloc_buffer > callbacks and check for kernel events as well. > > 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 > > Sai Prakash Ranjan (4): > perf/core: Export is_kernel_event() > coresight: tmc-etf: Fix NULL ptr dereference in > tmc_enable_etf_sink_perf() > coresight: etb10: Fix possible NULL ptr dereference in > etb_enable_perf() > coresight: tmc-etr: Fix possible NULL ptr dereference in > get_perf_etr_buf_cpu_wide() > > drivers/hwtracing/coresight/coresight-etb10.c | 8 +++++++- > drivers/hwtracing/coresight/coresight-priv.h | 2 ++ > drivers/hwtracing/coresight/coresight-tmc-etf.c | 8 +++++++- > drivers/hwtracing/coresight/coresight-tmc-etr.c | 6 +++++- > include/linux/perf_event.h | 2 ++ > kernel/events/core.c | 3 ++- > 6 files changed, 25 insertions(+), 4 deletions(-) > > > base-commit: f4cb5e9daedf56671badc93ac7f364043aa33886
Please ignore this series, I will need to resend.
Thanks, Sai
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