From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexey Budankov Subject: Re: [PATCH v5 01/10] capabilities: introduce CAP_PERFMON to kernel and user space Date: Wed, 12 Feb 2020 19:56:55 +0300 Message-ID: <950cc6a4-5823-d607-1210-6f62c96cf67f@linux.intel.com> References: <0548c832-7f4b-dc4c-8883-3f2b6d351a08@linux.intel.com> <9b77124b-675d-5ac7-3741-edec575bd425@linux.intel.com> <64cab472-806e-38c4-fb26-0ffbee485367@tycho.nsa.gov> <05297eff-8e14-ccdf-55a4-870c64516de8@linux.intel.com> <537bdb28-c9e4-f44f-d665-25250065a6bb@linux.intel.com> <63d9700f-231d-7973-5307-3e56a48c54cb@linux.intel.com> <2e38c33d-f085-1320-8cc2-45f74b6ad86d@linux.intel.com> <8141da2e-49cf-c02d-69e9-8a7cbdc91431@linux.intel.com> <7c367905-e8c9-7665-d923-c850e05c757a@tycho.nsa.gov> <280e6644-c129-15f6-ea5c-0f66bf764e0f@tycho.nsa.gov> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <280e6644-c129-15f6-ea5c-0f66bf764e0f@tycho.nsa.gov> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Stephen Smalley Cc: Alexei Starovoitov , Peter Zijlstra , Arnaldo Carvalho de Melo , Ingo Molnar , "jani.nikula@linux.intel.com" , "joonas.lahtinen@linux.intel.com" , "rodrigo.vivi@intel.com" , "benh@kernel.crashing.org" , Paul Mackerras , Michael Ellerman , "james.bottomley@hansenpartnership.com" , Serge Hallyn , James Morris , Will Deacon , Mark Rutland , Robert Richter , Alexei Starovoitov List-Id: linux-perf-users.vger.kernel.org On 12.02.2020 18:45, Stephen Smalley wrote: > On 2/12/20 10:21 AM, Stephen Smalley wrote: >> On 2/12/20 8:53 AM, Alexey Budankov wrote: >>> On 12.02.2020 16:32, Stephen Smalley wrote: >>>> On 2/12/20 3:53 AM, Alexey Budankov wrote: >>>>> Hi Stephen, >>>>> >>>>> On 22.01.2020 17:07, Stephen Smalley wrote: >>>>>> On 1/22/20 5:45 AM, Alexey Budankov wrote: >>>>>>> >>>>>>> On 21.01.2020 21:27, Alexey Budankov wrote: >>>>>>>> >>>>>>>> On 21.01.2020 20:55, Alexei Starovoitov wrote: >>>>>>>>> On Tue, Jan 21, 2020 at 9:31 AM Alexey Budankov >>>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> On 21.01.2020 17:43, Stephen Smalley wrote: >>>>>>>>>>> On 1/20/20 6:23 AM, Alexey Budankov wrote: >>>>>>>>>>>> >>>>> >>>>>>>>>>>> Introduce CAP_PERFMON capability designed to secure system performance >>>>>>>>>>> >>>>>>>>>>> Why _noaudit()?  Normally only used when a permission failure is non-fatal to the operation.  Otherwise, we want the audit message. >>>>>>> >>>>>>> So far so good, I suggest using the simplest version for v6: >>>>>>> >>>>>>> static inline bool perfmon_capable(void) >>>>>>> { >>>>>>>       return capable(CAP_PERFMON) || capable(CAP_SYS_ADMIN); >>>>>>> } >>>>>>> >>>>>>> It keeps the implementation simple and readable. The implementation is more >>>>>>> performant in the sense of calling the API - one capable() call for CAP_PERFMON >>>>>>> privileged process. >>>>>>> >>>>>>> Yes, it bloats audit log for CAP_SYS_ADMIN privileged and unprivileged processes, >>>>>>> but this bloating also advertises and leverages using more secure CAP_PERFMON >>>>>>> based approach to use perf_event_open system call. >>>>>> >>>>>> I can live with that.  We just need to document that when you see both a CAP_PERFMON and a CAP_SYS_ADMIN audit message for a process, try only allowing CAP_PERFMON first and see if that resolves the issue.  We have a similar issue with CAP_DAC_READ_SEARCH versus CAP_DAC_OVERRIDE. >>>>> >>>>> I am trying to reproduce this double logging with CAP_PERFMON. >>>>> I am using the refpolicy version with enabled perf_event tclass [1], in permissive mode. >>>>> When running perf stat -a I am observing this AVC audit messages: >>>>> >>>>> type=AVC msg=audit(1581496695.666:8691): avc:  denied  { open } for  pid=2779 comm="perf" scontext=user_u:user_r:user_systemd_t tcontext=user_u:user_r:user_systemd_t tclass=perf_event permissive=1 >>>>> type=AVC msg=audit(1581496695.666:8691): avc:  denied  { kernel } for  pid=2779 comm="perf" scontext=user_u:user_r:user_systemd_t tcontext=user_u:user_r:user_systemd_t tclass=perf_event permissive=1 >>>>> type=AVC msg=audit(1581496695.666:8691): avc:  denied  { cpu } for  pid=2779 comm="perf" scontext=user_u:user_r:user_systemd_t tcontext=user_u:user_r:user_systemd_t tclass=perf_event permissive=1 >>>>> type=AVC msg=audit(1581496695.666:8692): avc:  denied  { write } for  pid=2779 comm="perf" scontext=user_u:user_r:user_systemd_t tcontext=user_u:user_r:user_systemd_t tclass=perf_event permissive=1 >>>>> >>>>> However there is no capability related messages around. I suppose my refpolicy should >>>>> be modified somehow to observe capability related AVCs. >>>>> >>>>> Could you please comment or clarify on how to enable caps related AVCs in order >>>>> to test the concerned logging. >>>> >>>> The new perfmon permission has to be defined in your policy; you'll have a message in dmesg about "Permission perfmon in class capability2 not defined in policy.".  You can either add it to the common cap2 definition in refpolicy/policy/flask/access_vectors and rebuild your policy or extract your base module as CIL, add it there, and insert the updated module. >>> >>> Yes, I already have it like this: >>> common cap2 >>> { >>> <------>mac_override<--># unused by SELinux >>> <------>mac_admin >>> <------>syslog >>> <------>wake_alarm >>> <------>block_suspend >>> <------>audit_read >>> <------>perfmon >>> } >>> >>> dmesg stopped reporting perfmon as not defined but audit.log still doesn't report CAP_PERFMON denials. >>> BTW, audit even doesn't report CAP_SYS_ADMIN denials, however perfmon_capable() does check for it. >> >> Some denials may be silenced by dontaudit rules; semodule -DB will strip those and semodule -B will restore them.  Other possibility is that the process doesn't have CAP_PERFMON in its effective set and therefore never reaches SELinux at all; denied first by the capability module. > > Also, the fact that your denials are showing up in user_systemd_t suggests that something is off in your policy or userspace/distro; I assume that is a domain type for the systemd --user instance, but your shell and commands shouldn't be running in that domain (user_t would be more appropriate for that). It is user_t for local terminal session: ps -Z LABEL PID TTY TIME CMD user_u:user_r:user_t 11317 pts/9 00:00:00 bash user_u:user_r:user_t 11796 pts/9 00:00:00 ps For local terminal root session: ps -Z LABEL PID TTY TIME CMD user_u:user_r:user_su_t 2926 pts/3 00:00:00 bash user_u:user_r:user_su_t 10995 pts/3 00:00:00 ps For remote ssh session: ps -Z LABEL PID TTY TIME CMD user_u:user_r:user_t 7540 pts/8 00:00:00 ps user_u:user_r:user_systemd_t 8875 pts/8 00:00:00 bash ~Alexey