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