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

[Sai Prakash Ranjan]

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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