| Message ID | 751bd7d9fc65cdd3f1d118814193e9d925e2f56f.1601292571.git.saiprakash.ranjan@codeaurora.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Coresight ETF perf NULL pointer dereference and ETM save/restore fixes | expand |
On 2020-09-28 17:07, Sai Prakash Ranjan wrote: > There was a report of NULL pointer dereference in ETF enable > path for perf CS mode with PID. It is almost 100% reproducible > when the process to monitor is something very active such as > chrome and only with ETF as the sink. Currently in a bid to > find the pid, the owner is dereferenced via task_pid_nr() call > in tmc_enable_etf_sink_perf(). With owner being NULL, we get a > NULL pointer dereference, so check the owner before dereferencing > it to prevent the system crash. > > 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 > > 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 > +Peter, I could reproduce this (without my band-aid patch 100%) even on the latest coresight-next tip which is on 5.9-rc5 with my debian installed on SDM845 based board. Hi Peter, sorry to bother you. We observe that the NULL pointer is propagated from events core code(in the call trace below), is it even valid for the owner(task) to be NULL? Reproduction is as simple as below: perf record -e cs_etm/@tmc_etf0/ -N -p 1 [ 16.411231] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000468 [ 16.420080] Mem abort info: [ 16.422903] ESR = 0x96000004 [ 16.425988] EC = 0x25: DABT (current EL), IL = 32 bits [ 16.431345] SET = 0, FnV = 0 [ 16.434429] EA = 0, S1PTW = 0 [ 16.437602] Data abort info: [ 16.440506] ISV = 0, ISS = 0x00000004 [ 16.444377] CM = 0, WnR = 0 [ 16.447372] user pgtable: 4k pages, 48-bit VAs, pgdp=00000001f078c000 [ 16.453858] [0000000000000468] pgd=0000000000000000, p4d=0000000000000000 [ 16.460704] Internal error: Oops: 96000004 [#1] PREEMPT SMP [ 16.466323] Modules linked in: [ 16.469409] CPU: 5 PID: 2795 Comm: systemd Not tainted 5.9.0-rc5-g1aeb4770c2f1-dirty #6 [ 16.484046] pstate: 80400085 (Nzcv daIf +PAN -UAO BTYPE=--) [ 16.489668] pc : tmc_enable_etf_sink+0x74/0x2e8 [ 16.494237] lr : tmc_enable_etf_sink+0x50/0x2e8 [ 16.498807] sp : ffff800010c73b20 [ 16.502149] x29: ffff800010c73b20 x28: ffff0001712b0008 [ 16.507510] x27: ffff00017c76b308 x26: ffffa1e8a227dc80 [ 16.512860] x25: 0000000000000002 x24: ffff00017c766768 [ 16.518217] x23: 0000000000000080 x22: ffff000171c192e0 [ 16.523575] x21: ffff000173868000 x20: ffff000171c19280 [ 16.528934] x19: 0000000000000002 x18: ffffffffffffffff [ 16.534293] x17: 0000000000000000 x16: 0000000000000000 [ 16.539652] x15: ffffa1e8a1ec9948 x14: ffff800090c738a7 [ 16.545011] x13: ffff800010c738b5 x12: 0000000000000028 [ 16.550369] x11: ffffa1e8a1eea000 x10: 0000000000000000 [ 16.555728] x9 : 0000000000000000 x8 : 00000aeb00000aeb [ 16.561088] x7 : 003000000000000c x6 : 0000000000000001 [ 16.566447] x5 : 0000000000000002 x4 : 0000000000000001 [ 16.571805] x3 : 0000000000000000 x2 : 0000000000000001 [ 16.577163] x1 : 0000000000000000 x0 : 00000000ffffffff [ 16.582523] Call trace: [ 16.584998] tmc_enable_etf_sink+0x74/0x2e8 [ 16.589219] coresight_enable_path+0xd8/0x208 [ 16.593608] etm_event_start+0xe8/0x128 [ 16.597481] etm_event_add+0x44/0x60 [ 16.601094] event_sched_in.isra.139+0xd0/0x218 [ 16.605664] merge_sched_in+0x148/0x370 [ 16.609536] visit_groups_merge.constprop.147+0x124/0x490 [ 16.614973] ctx_sched_in+0xc4/0x168 [ 16.618575] perf_event_sched_in+0x6c/0xa8 [ 16.622706] __perf_event_task_sched_in+0x1a0/0x1b0 [ 16.627623] finish_task_switch+0x19c/0x248 [ 16.631843] schedule_tail+0x20/0x120 [ 16.635535] ret_from_fork+0x4/0x1c [ 16.639060] Code: 54000f20 f9400301 b9406680 f9414821 (b9446839) [ 16.645215] ---[ end trace bf238834e81d5892 ]--- [ 16.649877] Kernel panic - not syncing: Fatal exception Thanks, Sai
diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c index 44402d413ebb..32f141d943ca 100644 --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c @@ -242,6 +242,9 @@ static int tmc_enable_etf_sink_perf(struct coresight_device *csdev, void *data) break; } + if (!handle->event->owner) + break; + /* Get a handle on the pid of the process to monitor */ pid = task_pid_nr(handle->event->owner);
There was a report of NULL pointer dereference in ETF enable path for perf CS mode with PID. It is almost 100% reproducible when the process to monitor is something very active such as chrome and only with ETF as the sink. Currently in a bid to find the pid, the owner is dereferenced via task_pid_nr() call in tmc_enable_etf_sink_perf(). With owner being NULL, we get a NULL pointer dereference, so check the owner before dereferencing it to prevent the system crash. 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 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 Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org> --- I am not sure of this incomplete solution hence the RFC. This issue was also reported when this code was first added [1] but somehow it didn't get much notice at the time. So the NULL pointer is propagated from as far as flexible_sched_in() (might even be earlier than this) in events core and deferenced in ETF code where it crashes. So I am not sure if its a problem with the core code or the etf driver. Plus it is not reproducible with all the processes, just something which is quite active ones such as chrome. This is with 5.4 kernel with all the coresight patches backported, I did go through events/core code from latest kernel to see if we are missing any fixes related to this but I couldn't find any so I believe this problem should also exist on latest kernel as well. [1] https://lists.linaro.org/pipermail/coresight/2019-March/002278.html --- drivers/hwtracing/coresight/coresight-tmc-etf.c | 3 +++ 1 file changed, 3 insertions(+)