| Message ID | d7a2dd53d88360b12e5a14933cb931198760dd63.1602074787.git.saiprakash.ranjan@codeaurora.org (mailing list archive) |
|---|---|
| State | New, archived |
| 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
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
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 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 ? */ > Looking at it some more, is_kernel_event() is not exposed outside events core and probably for good reason. Why do we need to check for this and not just tsk? Thanks, Sai
On 10/14/2020 10:36 AM, Sai Prakash Ranjan wrote: > 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 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 ? */ >> > > Looking at it some more, is_kernel_event() is not exposed > outside events core and probably for good reason. Why do > we need to check for this and not just tsk? Because the event->owner could be : = NULL = -1UL // kernel event = valid. Kind regards Suzuki
On 2020-10-14 18:46, Suzuki K Poulose wrote: > On 10/14/2020 10:36 AM, Sai Prakash Ranjan wrote: >> 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 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 ? */ >>> >> >> Looking at it some more, is_kernel_event() is not exposed >> outside events core and probably for good reason. Why do >> we need to check for this and not just tsk? > > Because the event->owner could be : > > = NULL > = -1UL // kernel event > = valid. > Yes I understood that part, but here we were trying to fix the NULL pointer dereference right and hence the question as to why we need to check for kernel events? I am no expert in perf but I don't see anywhere in the kernel checking for is_kernel_event(), so I am a bit skeptical if exporting that is actually right or not. Thanks, Sai
On 2020-10-14 21:29, Sai Prakash Ranjan wrote: > On 2020-10-14 18:46, Suzuki K Poulose wrote: >> On 10/14/2020 10:36 AM, Sai Prakash Ranjan wrote: >>> 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 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 ? */ >>>> >>> >>> Looking at it some more, is_kernel_event() is not exposed >>> outside events core and probably for good reason. Why do >>> we need to check for this and not just tsk? >> >> Because the event->owner could be : >> >> = NULL >> = -1UL // kernel event >> = valid. >> > > Yes I understood that part, but here we were trying to > fix the NULL pointer dereference right and hence the > question as to why we need to check for kernel events? > I am no expert in perf but I don't see anywhere in the > kernel checking for is_kernel_event(), so I am a bit > skeptical if exporting that is actually right or not. > I have stress tested with the original patch many times now, i.e., without a check for event->owner and is_kernel_event() and didn't observe any crash. Plus on ETR where this was already done, no crashes were reported till date and with ETF, the issue was quickly reproducible, so I am fairly confident that this doesn't just delay the original issue but actually fixes it. I will run an overnight test again to confirm this. Thanks, Sai
On 2020-10-20 21:40, Sai Prakash Ranjan wrote: > On 2020-10-14 21:29, Sai Prakash Ranjan wrote: >> On 2020-10-14 18:46, Suzuki K Poulose wrote: >>> On 10/14/2020 10:36 AM, Sai Prakash Ranjan wrote: >>>> 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 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 ? */ >>>>> >>>> >>>> Looking at it some more, is_kernel_event() is not exposed >>>> outside events core and probably for good reason. Why do >>>> we need to check for this and not just tsk? >>> >>> Because the event->owner could be : >>> >>> = NULL >>> = -1UL // kernel event >>> = valid. >>> >> >> Yes I understood that part, but here we were trying to >> fix the NULL pointer dereference right and hence the >> question as to why we need to check for kernel events? >> I am no expert in perf but I don't see anywhere in the >> kernel checking for is_kernel_event(), so I am a bit >> skeptical if exporting that is actually right or not. >> > > I have stress tested with the original patch many times > now, i.e., without a check for event->owner and is_kernel_event() > and didn't observe any crash. Plus on ETR where this was already > done, no crashes were reported till date and with ETF, the issue > was quickly reproducible, so I am fairly confident that this > doesn't just delay the original issue but actually fixes > it. I will run an overnight test again to confirm this. > I ran the overnight test which collected aroung 4G data(see below), with the following small change to see if the two cases (event->owner=NULL and is_kernel_event()) are triggered with suggested changes and it didn't trigger at all. Do we still need those additional checks? [ perf record: Captured and wrote 4677.989 MB perf.data ] diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c index 989d965f3d90..123c446ce585 100644 --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c @@ -13,6 +13,13 @@ #include "coresight-tmc.h" #include "coresight-etm-perf.h" +#define TASK_TOMBSTONE ((void *)-1L) + +static bool is_kernel_event2(struct perf_event *event) +{ + return READ_ONCE(event->owner) == TASK_TOMBSTONE; +} + static int tmc_set_etf_buffer(struct coresight_device *csdev, struct perf_output_handle *handle); @@ -392,6 +399,15 @@ 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) { + pr_info("**sai in task=NULL**\n"); + return NULL; + } + + if (is_kernel_event2(event)) + pr_info("**sai in is_kernel_event**\n"); node = (event->cpu == -1) ? NUMA_NO_NODE : cpu_to_node(event->cpu); Thanks, Sai
On 10/21/20 8:29 AM, Sai Prakash Ranjan wrote: > On 2020-10-20 21:40, Sai Prakash Ranjan wrote: >> On 2020-10-14 21:29, Sai Prakash Ranjan wrote: >>> On 2020-10-14 18:46, Suzuki K Poulose wrote: >>>> On 10/14/2020 10:36 AM, Sai Prakash Ranjan wrote: >>>>> 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 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 ? */ >>>>>> >>>>> >>>>> Looking at it some more, is_kernel_event() is not exposed >>>>> outside events core and probably for good reason. Why do >>>>> we need to check for this and not just tsk? >>>> >>>> Because the event->owner could be : >>>> >>>> = NULL >>>> = -1UL // kernel event >>>> = valid. >>>> >>> >>> Yes I understood that part, but here we were trying to >>> fix the NULL pointer dereference right and hence the >>> question as to why we need to check for kernel events? >>> I am no expert in perf but I don't see anywhere in the >>> kernel checking for is_kernel_event(), so I am a bit >>> skeptical if exporting that is actually right or not. >>> >> >> I have stress tested with the original patch many times >> now, i.e., without a check for event->owner and is_kernel_event() >> and didn't observe any crash. Plus on ETR where this was already >> done, no crashes were reported till date and with ETF, the issue >> was quickly reproducible, so I am fairly confident that this >> doesn't just delay the original issue but actually fixes >> it. I will run an overnight test again to confirm this. >> > > I ran the overnight test which collected aroung 4G data(see below), > with the following small change to see if the two cases > (event->owner=NULL and is_kernel_event()) are triggered > with suggested changes and it didn't trigger at all. > Do we still need those additional checks? > Yes. Please see perf_event_create_kernel_event(), which is an exported function allowing any kernel code (including modules) to use the PMU (just like the userspace perf tool would do). Just because your use case doesn't trigger this (because you don't run something that can trigger this) doesn't mean this can't be triggered. Cheers Suzuki > [ perf record: Captured and wrote 4677.989 MB perf.data ] > > diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c > b/drivers/hwtracing/coresight/coresight-tmc-etf.c > index 989d965f3d90..123c446ce585 100644 > --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c > +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c > @@ -13,6 +13,13 @@ > #include "coresight-tmc.h" > #include "coresight-etm-perf.h" > > +#define TASK_TOMBSTONE ((void *)-1L) > + > +static bool is_kernel_event2(struct perf_event *event) > +{ > + return READ_ONCE(event->owner) == TASK_TOMBSTONE; > +} > + > static int tmc_set_etf_buffer(struct coresight_device *csdev, > struct perf_output_handle *handle); > > @@ -392,6 +399,15 @@ 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) { > + pr_info("**sai in task=NULL**\n"); > + return NULL; > + } > + > + if (is_kernel_event2(event)) > + pr_info("**sai in is_kernel_event**\n"); > > node = (event->cpu == -1) ? NUMA_NO_NODE : > cpu_to_node(event->cpu); > > > Thanks, > Sai >
On 2020-10-21 15:38, Suzuki Poulose wrote: > On 10/21/20 8:29 AM, Sai Prakash Ranjan wrote: >> On 2020-10-20 21:40, Sai Prakash Ranjan wrote: >>> On 2020-10-14 21:29, Sai Prakash Ranjan wrote: >>>> On 2020-10-14 18:46, Suzuki K Poulose wrote: >>>>> On 10/14/2020 10:36 AM, Sai Prakash Ranjan wrote: >>>>>> 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 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 ? */ >>>>>>> >>>>>> >>>>>> Looking at it some more, is_kernel_event() is not exposed >>>>>> outside events core and probably for good reason. Why do >>>>>> we need to check for this and not just tsk? >>>>> >>>>> Because the event->owner could be : >>>>> >>>>> = NULL >>>>> = -1UL // kernel event >>>>> = valid. >>>>> >>>> >>>> Yes I understood that part, but here we were trying to >>>> fix the NULL pointer dereference right and hence the >>>> question as to why we need to check for kernel events? >>>> I am no expert in perf but I don't see anywhere in the >>>> kernel checking for is_kernel_event(), so I am a bit >>>> skeptical if exporting that is actually right or not. >>>> >>> >>> I have stress tested with the original patch many times >>> now, i.e., without a check for event->owner and is_kernel_event() >>> and didn't observe any crash. Plus on ETR where this was already >>> done, no crashes were reported till date and with ETF, the issue >>> was quickly reproducible, so I am fairly confident that this >>> doesn't just delay the original issue but actually fixes >>> it. I will run an overnight test again to confirm this. >>> >> >> I ran the overnight test which collected aroung 4G data(see below), >> with the following small change to see if the two cases >> (event->owner=NULL and is_kernel_event()) are triggered >> with suggested changes and it didn't trigger at all. >> Do we still need those additional checks? >> > > Yes. Please see perf_event_create_kernel_event(), which is > an exported function allowing any kernel code (including modules) > to use the PMU (just like the userspace perf tool would do). > Just because your use case doesn't trigger this (because > you don't run something that can trigger this) doesn't mean > this can't be triggered. > Thanks for that pointer, I will add them in the next version. Thanks, Sai
On 10/22/20 9:02 AM, Sai Prakash Ranjan wrote: > On 2020-10-21 15:38, Suzuki Poulose wrote: >> On 10/21/20 8:29 AM, Sai Prakash Ranjan wrote: >>> On 2020-10-20 21:40, Sai Prakash Ranjan wrote: >>>> On 2020-10-14 21:29, Sai Prakash Ranjan wrote: >>>>> On 2020-10-14 18:46, Suzuki K Poulose wrote: >>>>>> On 10/14/2020 10:36 AM, Sai Prakash Ranjan wrote: >>>>>>> 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 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 ? */ >>>>>>>> >>>>>>> >>>>>>> Looking at it some more, is_kernel_event() is not exposed >>>>>>> outside events core and probably for good reason. Why do >>>>>>> we need to check for this and not just tsk? >>>>>> >>>>>> Because the event->owner could be : >>>>>> >>>>>> = NULL >>>>>> = -1UL // kernel event >>>>>> = valid. >>>>>> >>>>> >>>>> Yes I understood that part, but here we were trying to >>>>> fix the NULL pointer dereference right and hence the >>>>> question as to why we need to check for kernel events? >>>>> I am no expert in perf but I don't see anywhere in the >>>>> kernel checking for is_kernel_event(), so I am a bit >>>>> skeptical if exporting that is actually right or not. >>>>> >>>> >>>> I have stress tested with the original patch many times >>>> now, i.e., without a check for event->owner and is_kernel_event() >>>> and didn't observe any crash. Plus on ETR where this was already >>>> done, no crashes were reported till date and with ETF, the issue >>>> was quickly reproducible, so I am fairly confident that this >>>> doesn't just delay the original issue but actually fixes >>>> it. I will run an overnight test again to confirm this. >>>> >>> >>> I ran the overnight test which collected aroung 4G data(see below), >>> with the following small change to see if the two cases >>> (event->owner=NULL and is_kernel_event()) are triggered >>> with suggested changes and it didn't trigger at all. >>> Do we still need those additional checks? >>> >> >> Yes. Please see perf_event_create_kernel_event(), which is >> an exported function allowing any kernel code (including modules) >> to use the PMU (just like the userspace perf tool would do). >> Just because your use case doesn't trigger this (because >> you don't run something that can trigger this) doesn't mean >> this can't be triggered. >> > > Thanks for that pointer, I will add them in the next version. > And instead of redefining TASK_TOMBSTONE in the driver, you may simply use IS_ERR_OR_NULL(tsk) to cover both NULL case and kernel event. Cheers Suzuki
On 2020-10-22 14:57, Suzuki Poulose wrote: > On 10/22/20 9:02 AM, Sai Prakash Ranjan wrote: >> On 2020-10-21 15:38, Suzuki Poulose wrote: >>> On 10/21/20 8:29 AM, Sai Prakash Ranjan wrote: >>>> On 2020-10-20 21:40, Sai Prakash Ranjan wrote: >>>>> On 2020-10-14 21:29, Sai Prakash Ranjan wrote: >>>>>> On 2020-10-14 18:46, Suzuki K Poulose wrote: >>>>>>> On 10/14/2020 10:36 AM, Sai Prakash Ranjan wrote: >>>>>>>> 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 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 ? */ >>>>>>>>> >>>>>>>> >>>>>>>> Looking at it some more, is_kernel_event() is not exposed >>>>>>>> outside events core and probably for good reason. Why do >>>>>>>> we need to check for this and not just tsk? >>>>>>> >>>>>>> Because the event->owner could be : >>>>>>> >>>>>>> = NULL >>>>>>> = -1UL // kernel event >>>>>>> = valid. >>>>>>> >>>>>> >>>>>> Yes I understood that part, but here we were trying to >>>>>> fix the NULL pointer dereference right and hence the >>>>>> question as to why we need to check for kernel events? >>>>>> I am no expert in perf but I don't see anywhere in the >>>>>> kernel checking for is_kernel_event(), so I am a bit >>>>>> skeptical if exporting that is actually right or not. >>>>>> >>>>> >>>>> I have stress tested with the original patch many times >>>>> now, i.e., without a check for event->owner and is_kernel_event() >>>>> and didn't observe any crash. Plus on ETR where this was already >>>>> done, no crashes were reported till date and with ETF, the issue >>>>> was quickly reproducible, so I am fairly confident that this >>>>> doesn't just delay the original issue but actually fixes >>>>> it. I will run an overnight test again to confirm this. >>>>> >>>> >>>> I ran the overnight test which collected aroung 4G data(see below), >>>> with the following small change to see if the two cases >>>> (event->owner=NULL and is_kernel_event()) are triggered >>>> with suggested changes and it didn't trigger at all. >>>> Do we still need those additional checks? >>>> >>> >>> Yes. Please see perf_event_create_kernel_event(), which is >>> an exported function allowing any kernel code (including modules) >>> to use the PMU (just like the userspace perf tool would do). >>> Just because your use case doesn't trigger this (because >>> you don't run something that can trigger this) doesn't mean >>> this can't be triggered. >>> >> >> Thanks for that pointer, I will add them in the next version. >> > > And instead of redefining TASK_TOMBSTONE in the driver, you > may simply use IS_ERR_OR_NULL(tsk) to cover both NULL case > and kernel event. > Ugh sorry, sent out v2 exporting is_kernel_event() before seeing this comment, I will resend. Thanks, Sai
On 10/22/20 12:07 PM, Sai Prakash Ranjan wrote: > On 2020-10-22 14:57, Suzuki Poulose wrote: >> On 10/22/20 9:02 AM, Sai Prakash Ranjan wrote: >>> On 2020-10-21 15:38, Suzuki Poulose wrote: >>>> On 10/21/20 8:29 AM, Sai Prakash Ranjan wrote: >>>>> On 2020-10-20 21:40, Sai Prakash Ranjan wrote: >>>>>> On 2020-10-14 21:29, Sai Prakash Ranjan wrote: >>>>>>> On 2020-10-14 18:46, Suzuki K Poulose wrote: >>>>>>>> On 10/14/2020 10:36 AM, Sai Prakash Ranjan wrote: >>>>>>>>> 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 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 ? */ >>>>>>>>>> >>>>>>>>> >>>>>>>>> Looking at it some more, is_kernel_event() is not exposed >>>>>>>>> outside events core and probably for good reason. Why do >>>>>>>>> we need to check for this and not just tsk? >>>>>>>> >>>>>>>> Because the event->owner could be : >>>>>>>> >>>>>>>> = NULL >>>>>>>> = -1UL // kernel event >>>>>>>> = valid. >>>>>>>> >>>>>>> >>>>>>> Yes I understood that part, but here we were trying to >>>>>>> fix the NULL pointer dereference right and hence the >>>>>>> question as to why we need to check for kernel events? >>>>>>> I am no expert in perf but I don't see anywhere in the >>>>>>> kernel checking for is_kernel_event(), so I am a bit >>>>>>> skeptical if exporting that is actually right or not. >>>>>>> >>>>>> >>>>>> I have stress tested with the original patch many times >>>>>> now, i.e., without a check for event->owner and is_kernel_event() >>>>>> and didn't observe any crash. Plus on ETR where this was already >>>>>> done, no crashes were reported till date and with ETF, the issue >>>>>> was quickly reproducible, so I am fairly confident that this >>>>>> doesn't just delay the original issue but actually fixes >>>>>> it. I will run an overnight test again to confirm this. >>>>>> >>>>> >>>>> I ran the overnight test which collected aroung 4G data(see below), >>>>> with the following small change to see if the two cases >>>>> (event->owner=NULL and is_kernel_event()) are triggered >>>>> with suggested changes and it didn't trigger at all. >>>>> Do we still need those additional checks? >>>>> >>>> >>>> Yes. Please see perf_event_create_kernel_event(), which is >>>> an exported function allowing any kernel code (including modules) >>>> to use the PMU (just like the userspace perf tool would do). >>>> Just because your use case doesn't trigger this (because >>>> you don't run something that can trigger this) doesn't mean >>>> this can't be triggered. >>>> >>> >>> Thanks for that pointer, I will add them in the next version. >>> >> >> And instead of redefining TASK_TOMBSTONE in the driver, you >> may simply use IS_ERR_OR_NULL(tsk) to cover both NULL case >> and kernel event. >> > > Ugh sorry, sent out v2 exporting is_kernel_event() before seeing > this comment, I will resend. Saw that. I would say, wait until someone complains about that. If people are Ok with exporting it, it is fine. I guess it will be useful. You could fall back to this approach if there is resistance. Cheers Suzuki
On 2020-10-22 16:44, Suzuki Poulose wrote: > On 10/22/20 12:07 PM, Sai Prakash Ranjan wrote: >> On 2020-10-22 14:57, Suzuki Poulose wrote: >>> On 10/22/20 9:02 AM, Sai Prakash Ranjan wrote: >>>> On 2020-10-21 15:38, Suzuki Poulose wrote: >>>>> On 10/21/20 8:29 AM, Sai Prakash Ranjan wrote: >>>>>> On 2020-10-20 21:40, Sai Prakash Ranjan wrote: >>>>>>> On 2020-10-14 21:29, Sai Prakash Ranjan wrote: >>>>>>>> On 2020-10-14 18:46, Suzuki K Poulose wrote: >>>>>>>>> On 10/14/2020 10:36 AM, Sai Prakash Ranjan wrote: >>>>>>>>>> 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 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 ? */ >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>> Looking at it some more, is_kernel_event() is not exposed >>>>>>>>>> outside events core and probably for good reason. Why do >>>>>>>>>> we need to check for this and not just tsk? >>>>>>>>> >>>>>>>>> Because the event->owner could be : >>>>>>>>> >>>>>>>>> = NULL >>>>>>>>> = -1UL // kernel event >>>>>>>>> = valid. >>>>>>>>> >>>>>>>> >>>>>>>> Yes I understood that part, but here we were trying to >>>>>>>> fix the NULL pointer dereference right and hence the >>>>>>>> question as to why we need to check for kernel events? >>>>>>>> I am no expert in perf but I don't see anywhere in the >>>>>>>> kernel checking for is_kernel_event(), so I am a bit >>>>>>>> skeptical if exporting that is actually right or not. >>>>>>>> >>>>>>> >>>>>>> I have stress tested with the original patch many times >>>>>>> now, i.e., without a check for event->owner and is_kernel_event() >>>>>>> and didn't observe any crash. Plus on ETR where this was already >>>>>>> done, no crashes were reported till date and with ETF, the issue >>>>>>> was quickly reproducible, so I am fairly confident that this >>>>>>> doesn't just delay the original issue but actually fixes >>>>>>> it. I will run an overnight test again to confirm this. >>>>>>> >>>>>> >>>>>> I ran the overnight test which collected aroung 4G data(see >>>>>> below), >>>>>> with the following small change to see if the two cases >>>>>> (event->owner=NULL and is_kernel_event()) are triggered >>>>>> with suggested changes and it didn't trigger at all. >>>>>> Do we still need those additional checks? >>>>>> >>>>> >>>>> Yes. Please see perf_event_create_kernel_event(), which is >>>>> an exported function allowing any kernel code (including modules) >>>>> to use the PMU (just like the userspace perf tool would do). >>>>> Just because your use case doesn't trigger this (because >>>>> you don't run something that can trigger this) doesn't mean >>>>> this can't be triggered. >>>>> >>>> >>>> Thanks for that pointer, I will add them in the next version. >>>> >>> >>> And instead of redefining TASK_TOMBSTONE in the driver, you >>> may simply use IS_ERR_OR_NULL(tsk) to cover both NULL case >>> and kernel event. >>> >> >> Ugh sorry, sent out v2 exporting is_kernel_event() before seeing >> this comment, I will resend. > > Saw that. I would say, wait until someone complains about that. If > people are Ok with exporting it, it is fine. I guess it will be useful. > You could fall back to this approach if there is resistance. > Sure, I will wait for some comments although I hurried to tell them to ignore it :( Thanks, Sai
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(-)