Date: Tue, 27 Nov 2018 11:15:37 +0300 From: Alexey Budankov <alexey.budankov@...ux.intel.com> To: Jonatan Corbet <corbet@....net>, Thomas Gleixner <tglx@...utronix.de>, Kees Cook <keescook@...omium.org>, Jann Horn <jannh@...gle.com>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Andi Kleen <ak@...ux.intel.com> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, Tvrtko Ursulin <tursulin@...ulin.net>, linux-kernel <linux-kernel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org> Subject: [PATCH v4 1/2] Documentation/admin-guide: introduce perf-security.rst file Implement initial version of perf-security.rst documentation file covering security concerns of perf_event_paranoid settings. Suggested-by: Thomas Gleixner <tglx@...utronix.de> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com> --- Changes in v4: - added docs for perf_event related capabilities Changes in v3: - toning down of the markup for "scope, access and resource" - adding definite article for "Linux implementation" Changes in v2: - reverted patches order in the set to avoid CI issue - replaced old PCL referencing by PE (Perf Events) - skipped >=3 setting documentation at the moment --- Documentation/admin-guide/perf-security.rst | 97 +++++++++++++++++++++ 1 file changed, 97 insertions(+) create mode 100644 Documentation/admin-guide/perf-security.rst diff --git a/Documentation/admin-guide/perf-security.rst b/Documentation/admin-guide/perf-security.rst new file mode 100644 index 000000000000..f73ebfe9bfe2 --- /dev/null +++ b/Documentation/admin-guide/perf-security.rst @@ -0,0 +1,97 @@ +.. _perf_security: + +Perf Events and tool security +============================= + +Overview +-------- + +Usage of Performance Counters for Linux (perf_events) _ , _ , _ can +impose a considerable risk of leaking sensitive data accessed by monitored +processes. The data leakage is possible both in scenarios of direct usage of +perf_events system call API _ and over data files generated by Perf tool user +mode utility (Perf) _ , _ . The risk depends on the nature of data that +perf_events performance monitoring units (PMU) _ collect and expose for +performance analysis. Having that said perf_events/Perf performance monitoring +is the subject for security access control management _ . + +perf_events/Perf access control +------------------------------- + +To perform security checks, the Linux implementation splits processes into two +categories _ : a) privileged processes (whose effective user ID is 0, referred +to as superuser or root), and b) unprivileged processes (whose effective UID is +nonzero). Privileged processes bypass all kernel security permission checks so +perf_events performance monitoring is fully available to privileged processes +without access, scope and resource restrictions. + +Unprivileged processes are subject to a full security permission check based on +the process's credentials _ (usually: effective UID, effective GID, and +supplementary group list). + +Linux divides the privileges traditionally associated with superuser into +distinct units, known as capabilities _ , which can be independently enabled +and disabled on per-thread basis for processes and files of unprivileged users. + +Unprivileged processes with enabled CAP_SYS_ADMIN capability are treated as +privileged processes with respect to perf_events performance monitoring and +bypass *scope* permissions checks in the kernel. + +Unprivileged processes using perf_events system call API is also subject for +PTRACE_MODE_READ_REALCREDS ptrace access mode check _ , whose outcome +determines whether monitoring is permitted. So unprivileged processes provided +with CAP_SYS_PTRACE capability are effectively permitted to pass the check. + +Other capabilities being granted to unprivileged processes can effectively +enable capturing of additional data required for later performance analysis of +monitored processes or a system. For example, CAP_SYSLOG capability permits +reading kernel space memory addresses from /proc/kallsyms file. + +perf_events/Perf unprivileged users +----------------------------------- + +perf_events/Perf *scope* and *access* control for unprivileged processes is +governed by perf_event_paranoid _ setting: + +-1: + Impose no *scope* and *access* restrictions on using perf_events performance + monitoring. Per-user per-cpu perf_event_mlock_kb _ locking limit is + ignored when allocating memory buffers for storing performance data. + This is the least secure mode since allowed monitored *scope* is + maximized and no perf_events specific limits are imposed on *resources* + allocated for performance monitoring. + +>=0: + *scope* includes per-process and system wide performance monitoring + but excludes raw tracepoints and ftrace function tracepoints monitoring. + CPU and system events happened when executing either in user or + in kernel space can be monitored and captured for later analysis. + Per-user per-cpu perf_event_mlock_kb locking limit is imposed but + ignored for unprivileged processes with CAP_IPC_LOCK _ capability. + +>=1: + *scope* includes per-process performance monitoring only and excludes + system wide performance monitoring. CPU and system events happened when + executing either in user or in kernel space can be monitored and + captured for later analysis. Per-user per-cpu perf_event_mlock_kb + locking limit is imposed but ignored for unprivileged processes with + CAP_IPC_LOCK capability. + +>=2: + *scope* includes per-process performance monitoring only. CPU and system + events happened when executing in user space only can be monitored and + captured for later analysis. Per-user per-cpu perf_event_mlock_kb + locking limit is imposed but ignored for unprivileged processes with + CAP_IPC_LOCK capability. + +Bibliography +------------ + +..  `<https://lwn.net/Articles/337493/>`_ +..  `<http://man7.org/linux/man-pages/man2/perf_event_open.2.html>`_ +..  `<http://web.eece.maine.edu/~vweaver/projects/perf_events/>`_ +..  `<https://perf.wiki.kernel.org/index.php/Main_Page>`_ +..  `<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>`_ +
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