Date: Fri, 1 Feb 2019 10:29:11 +0300 From: Alexey Budankov <alexey.budankov@...ux.intel.com> To: Jonatan Corbet <corbet@....net>, Kees Cook <keescook@...omium.org>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org> Cc: Jann Horn <jannh@...gle.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Mark Rutland <mark.rutland@....com>, Andi Kleen <ak@...ux.intel.com>, Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, linux-kernel <linux-kernel@...r.kernel.org> Subject: [PATCH v1 1/3] perf-security: document perf_events/Perf resource control Extend perf-security.rst file with perf_events/Perf resource control section describing RLIMIT_NOFILE and perf_event_mlock_kb settings for performance monitoring user processes. Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com> --- Documentation/admin-guide/perf-security.rst | 36 +++++++++++++++++++++ 1 file changed, 36 insertions(+) diff --git a/Documentation/admin-guide/perf-security.rst b/Documentation/admin-guide/perf-security.rst index f73ebfe9bfe2..ff6832191577 100644 --- a/Documentation/admin-guide/perf-security.rst +++ b/Documentation/admin-guide/perf-security.rst @@ -84,6 +84,40 @@ governed by perf_event_paranoid _ setting: locking limit is imposed but ignored for unprivileged processes with CAP_IPC_LOCK capability. +perf_events/Perf resource control +--------------------------------- + +perf_events system call API _ allocates file descriptors for every configured +PMU event. Open file descriptors are a per-process accountable *resource* governed +by RLIMIT_NOFILE _ limit (ulimit -n), which is usually derived from the login +shell process. When configuring Perf collection for a long list of events on a +large server system, this limit can be easily hit preventing required monitoring +configuration. RLIMIT_NOFILE limit can be increased on per-user basis modifying +content of limits.conf file _ on some systems. Ordinary Perf sampling session +(perf record) requires an amount of open perf_event file descriptors that is not +less than a number of monitored events multiplied by a number of monitored CPUs. + +An amount of memory available to user processes for capturing performance monitoring +data is governed by perf_event_mlock_kb _ setting. This perf_event specific +*resource* setting defines overall per-cpu limits of memory allowed for mapping +by the user processes to execute performance monitoring. The setting essentially +extends RLIMIT_MEMLOCK _ limit but only for memory regions mapped specially +for capturing monitored performance events and related data. + +For example, if a machine has eight cores and perf_event_mlock_kb limit is set +to 516 KiB then a user process is provided with 516 KiB * 8 = 4128 KiB of memory +above RLIMIT_MEMLOCK limit (ulimit -l) for perf_event mmap buffers. In particular +this means that if the user wants to start two or more performance monitoring +processes, it is required to manually distribute available 4128 KiB between the +monitoring processes, for example, using --mmap-pages Perf record mode option. +Otherwise, the first started performance monitoring process allocates all available +4128 KiB and the other processes will fail to proceed due to the lack of memory. + +RLIMIT_MEMLOCK and perf_event_mlock_kb *resource* constraints are ignored for +processes with CAP_IPC_LOCK capability. Thus, perf_events/Perf privileged users +can be provided with memory above the constraints for perf_events/Perf performance +monitoring purpose by providing the Perf executable with CAP_IPC_LOCK capability. + Bibliography ------------ @@ -94,4 +128,6 @@ Bibliography ..  `<https://www.kernel.org/doc/html/latest/security/credentials.html>`_ ..  `<http://man7.org/linux/man-pages/man7/capabilities.7.html>`_ ..  `<http://man7.org/linux/man-pages/man2/ptrace.2.html>`_ +..  `<http://man7.org/linux/man-pages/man2/getrlimit.2.html>`_ +..  `<http://man7.org/linux/man-pages/man5/limits.conf.5.html>`_
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