Re: [PATCH v4 1/2] selinux: add tracepoint on audited events

[Stephen Smalley]

On Fri, Aug 21, 2020 at 10:09 AM Thiébaud Weksteen <tweek@xxxxxxxxxx> wrote:
>
> The audit data currently captures which process and which target
> is responsible for a denial. There is no data on where exactly in the
> process that call occurred. Debugging can be made easier by being able to
> reconstruct the unified kernel and userland stack traces [1]. Add a
> tracepoint on the SELinux denials which can then be used by userland
> (i.e. perf).
>
> Although this patch could manually be added by each OS developer to
> trouble shoot a denial, adding it to the kernel streamlines the
> developers workflow.
>
> It is possible to use perf for monitoring the event:
>   # perf record -e avc:selinux_audited -g -a
>   ^C
>   # perf report -g
>   [...]
>       6.40%     6.40%  audited=800000 tclass=4
>                |
>                   __libc_start_main
>                   |
>                   |--4.60%--__GI___ioctl
>                   |          entry_SYSCALL_64
>                   |          do_syscall_64
>                   |          __x64_sys_ioctl
>                   |          ksys_ioctl
>                   |          binder_ioctl
>                   |          binder_set_nice
>                   |          can_nice
>                   |          capable
>                   |          security_capable
>                   |          cred_has_capability.isra.0
>                   |          slow_avc_audit
>                   |          common_lsm_audit
>                   |          avc_audit_post_callback
>                   |          avc_audit_post_callback
>                   |
>
> It is also possible to use the ftrace interface:
>   # echo 1 > /sys/kernel/debug/tracing/events/avc/selinux_audited/enable
>   # cat /sys/kernel/debug/tracing/trace
>   tracer: nop
>   entries-in-buffer/entries-written: 1/1   #P:8
>   [...]
>   dmesg-3624  [001] 13072.325358: selinux_denied: audited=800000 tclass=4
>
> The tclass value can be mapped to a class by searching
> security/selinux/flask.h. The audited value is a bit field of the
> permissions described in security/selinux/av_permissions.h for the
> corresponding class.
>
> [1] https://source.android.com/devices/tech/debug/native_stack_dump
>
> Signed-off-by: Thiébaud Weksteen <tweek@xxxxxxxxxx>
> Suggested-by: Joel Fernandes <joelaf@xxxxxxxxxx>
> Reviewed-by: Peter Enderborg <peter.enderborg@xxxxxxxx>

Acked-by: Stephen Smalley <stephen.smalley.work@xxxxxxxxx>