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[68.134.6.11]) by smtp.gmail.com with ESMTPSA id y3sm7176981qtj.55.2020.08.13.08.41.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Aug 2020 08:41:49 -0700 (PDT) Subject: Re: [PATCH v2 1/2] selinux: add tracepoint on denials To: =?UTF-8?Q?Thi=c3=a9baud_Weksteen?= , Paul Moore Cc: Nick Kralevich , Joel Fernandes , Peter Enderborg , Eric Paris , Steven Rostedt , Ingo Molnar , Mauro Carvalho Chehab , "David S. Miller" , Rob Herring , Arnd Bergmann , linux-kernel@vger.kernel.org, selinux@vger.kernel.org References: <20200813144914.737306-1-tweek@google.com> From: Stephen Smalley 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 List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.