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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) [1]_ , [2]_ , [3]_ 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 [2]_ and over data files generated by Perf tool user +mode utility (Perf) [3]_ , [4]_ . The risk depends on the nature of data that +perf_events performance monitoring units (PMU) [2]_ collect and expose for +performance analysis. Having that said perf_events/Perf performance monitoring +is the subject for security access control management [5]_ . + +perf_events/Perf access control +------------------------------- + +To perform security checks, the Linux implementation splits processes into two +categories [6]_ : 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 [5]_ (usually: effective UID, effective GID, and +supplementary group list). + +Linux divides the privileges traditionally associated with superuser into +distinct units, known as capabilities [6]_ , 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 [7]_ , 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 [2]_ setting: + +-1: + Impose no *scope* and *access* restrictions on using perf_events performance + monitoring. Per-user per-cpu perf_event_mlock_kb [2]_ 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 [6]_ 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 +------------ + +.. [1] `<https://lwn.net/Articles/337493/>`_ +.. [2] `<http://man7.org/linux/man-pages/man2/perf_event_open.2.html>`_ +.. [3] `<http://web.eece.maine.edu/~vweaver/projects/perf_events/>`_ +.. [4] `<https://perf.wiki.kernel.org/index.php/Main_Page>`_ +.. [5] `<https://www.kernel.org/doc/html/latest/security/credentials.html>`_ +.. [6] `<http://man7.org/linux/man-pages/man7/capabilities.7.html>`_ +.. [7] `<http://man7.org/linux/man-pages/man2/ptrace.2.html>`_ + |