Date: Mon, 19 Nov 2018 18:12:23 +0300 From: Alexey Budankov <alexey.budankov@...ux.intel.com> To: Greg KH <gregkh@...uxfoundation.org> Cc: 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>, 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, linux-doc@...r.kernel.org Subject: Re: [PATCH v1 1/2]: Documentation/admin-guide: update admin-guide index.rst Hello Greg, On 19.11.2018 13:03, Greg KH wrote: > On Mon, Nov 19, 2018 at 08:41:31AM +0300, Alexey Budankov wrote: >> >> Extend index.rst index file at admin-guide root directory with >> the reference to perf-security.rst file being introduced. >> >> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com> >> --- >> Documentation/admin-guide/index.rst | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/Documentation/admin-guide/index.rst b/Documentation/admin-guide/index.rst >> index 0873685bab0f..885cc0de9114 100644 >> --- a/Documentation/admin-guide/index.rst >> +++ b/Documentation/admin-guide/index.rst >> @@ -75,6 +75,7 @@ configure specific aspects of kernel behavior to your liking. >> thunderbolt >> LSM/index >> mm/index >> + perf-security > > You just broke the build with this patch. They need to be ordered the > other way around :( Thanks for pointing that out. The patches are now rebased according to MAINTAINERS here: git://git.lwn.net/linux.git docs-next make htmldocs SPHINXDIRS=admin-guide worked for me: ... build succeeded, 10 warnings. The HTML pages are in Documentation/output/admin-guide. firefox Documentation/output/admin-guide/index.html shows link to the document at the end of this paragraph: "The rest of this manual consists of various unordered guides on how to \ configure specific aspects of kernel behavior to your liking." Rebased changes are below for your convenience. Thanks, Alexey --- Documentation/admin-guide/index.rst | 1 + Documentation/admin-guide/perf-security.rst | 83 +++++++++++++++++++++++++++++ 2 files changed, 84 insertions(+) diff --git a/Documentation/admin-guide/index.rst b/Documentation/admin-guide/index.rst index 965745d5fb9a..0a491676685e 100644 --- a/Documentation/admin-guide/index.rst +++ b/Documentation/admin-guide/index.rst @@ -76,6 +76,7 @@ configure specific aspects of kernel behavior to your liking. thunderbolt LSM/index mm/index + perf-security .. only:: subproject and html diff --git a/Documentation/admin-guide/perf-security.rst b/Documentation/admin-guide/perf-security.rst new file mode 100644 index 000000000000..b9564066e686 --- /dev/null +++ b/Documentation/admin-guide/perf-security.rst @@ -0,0 +1,83 @@ +.. _perf_security: + +PCL/Perf security +================= + +Overview +-------- + +Usage of Performance Counters for Linux (PCL) _ , _ , _ 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 PCL system +call API _ and over data files generated by Perf tool user mode utility +(Perf) _ , _ . The risk depends on the nature of data that PCL performance +monitoring units (PMU) _ collect and expose for performance analysis. +Having that said PCL/Perf performance monitoring is the subject for security +access control management _ . + +PCL/Perf access control +----------------------- + +For the purpose of performing security checks 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 PCL 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 _ (usually: effective UID, effective GID, +and supplementary group list). + +PCL/Perf unprivileged users +--------------------------- + +PCL/Perf *scope* and *access* control for unprivileged processes is governed by +perf_event_paranoid _ setting: + +**-1**: + Impose no *scope* and *access* restrictions on using PCL 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 PCL 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. + +**>=3**: + Restrict *access* to PCL performance monitoring for unprivileged processes. + This is the default on Debian and Android _ , _ . + +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>`_ +..  `<https://lkml.org/lkml/2016/1/11/587>`_ +..  `<https://android-review.googlesource.com/#/c/234743/>`_ +
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