linux-kernel - Re: [PATCH v3 1/3] selinux: add tracepoint on audited events

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Date:   Tue, 18 Aug 2020 10:31:11 -0400
From:   Stephen Smalley <stephen.smalley.work@...il.com>
To:     Thiébaud Weksteen <tweek@...gle.com>,
        Paul Moore <paul@...l-moore.com>
Cc:     Nick Kralevich <nnk@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Peter Enderborg <peter.enderborg@...y.com>,
        Eric Paris <eparis@...isplace.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh@...nel.org>, linux-kernel@...r.kernel.org,
        selinux@...r.kernel.org
Subject: Re: [PATCH v3 1/3] selinux: add tracepoint on audited events

On 8/17/20 1:07 PM, Thiébaud Weksteen 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@...gle.com>
> Suggested-by: Joel Fernandes <joelaf@...gle.com>
> Reviewed-by: Peter Enderborg <peter.enderborg@...y.com>
Acked-by: Stephen Smalley <stephen.smalley.work@...il.com>