Re: [PATCHv2 0/4] coresight: etf/etb10/etr: Fix NULL pointer dereference crashes

[Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>]

On 2020-10-22 16:40, Sai Prakash Ranjan wrote:
> 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.
> 

Please ignore my previous ignore request and let me
know if exporting is_kernel_event() is ok.

Thanks,
Sai

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