Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v2 1/2] selinux: add tracepoint on denials
To:     =?UTF-8?Q?Thi=c3=a9baud_Weksteen?= <tweek@google.com>,
        Paul Moore <paul@paul-moore.com>
Cc:     Nick Kralevich <nnk@google.com>,
        Joel Fernandes <joelaf@google.com>,
        Peter Enderborg <peter.enderborg@sony.com>,
        Eric Paris <eparis@parisplace.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Rob Herring <robh@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        linux-kernel@vger.kernel.org, selinux@vger.kernel.org
References: <20200813144914.737306-1-tweek@google.com>
From:   Stephen Smalley <stephen.smalley.work@gmail.com>
Message-ID: <15e2e26d-fe4b-679c-b5c0-c96d56e09853@gmail.com>
Date:   Thu, 13 Aug 2020 11:41:48 -0400
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <20200813144914.737306-1-tweek@google.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 8/13/20 10:48 AM, 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

An explanation here of how one might go about decoding audited and 
tclass would be helpful to users (even better would be a script to do it 
for them).  Again, I know how to do that but not everyone using 
perf/ftrace will.