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Date: Tue, 20 Nov 2018 12:27:55 +0300
From: Alexey Budankov <alexey.budankov@...ux.intel.com>
To: 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>,
Arnaldo Carvalho de Melo <acme@...nel.org>, Andi Kleen <ak@...ux.intel.com>,
Jonatan Corbet <corbet@....net>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...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 v2 1/2] Documentation/admin-guide: introduce perf-security.rst
file
Implement initial version of perf-security.rst documentation file
initially covering security concerns related to PE/Perf performance
monitoring in multiuser environments.
Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
---
Changes in v2:
- replaced old PCL referencing by PE (Perf Events)
- skipped >=3 setting documentation at the moment
---
Documentation/admin-guide/perf-security.rst | 76 +++++++++++++++++++++
1 file changed, 76 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..d9dcea61ed87
--- /dev/null
+++ b/Documentation/admin-guide/perf-security.rst
@@ -0,0 +1,76 @@
+.. _perf_security:
+
+Perf Events and tool security
+=============================
+
+Overview
+--------
+
+Usage of Perf Events (PE) [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 PE 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 PE performance monitoring units (PMU) [2]_
+collect and expose for performance analysis. Having that said PE/Perf performance
+monitoring is the subject for security access control management [5]_ .
+
+PE/Perf access control
+----------------------
+
+For the purpose of performing security checks 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 PE performance monitoring is fully available to
+privileged processes without *access*, *scope* and *resource* restrictions.
+Unprivileged processes are subject to full security permission check based
+on the process's credentials [5]_ (usually: effective UID, effective GID,
+and supplementary group list).
+
+PE/Perf unprivileged users
+--------------------------
+
+PE/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 PE 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 PE 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>`_
+
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