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