linux-kernel - [PATCH v1] perf_event_open.2: update the man page with CAP

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Date:   Mon, 17 Feb 2020 11:18:55 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:     linux-man@...r.kernel.org, James Morris <jmorris@...ei.org>,
        Serge Hallyn <serge@...lyn.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH v1] perf_event_open.2: update the man page with CAP_PERFMON
 related information


Extend perf_event_open 2 man page with the information about
CAP_PERFMON capability designed to secure performance monitoring
and observability operation in a system according to the principle
of least privilege [1] (POSIX IEEE 1003.1e, 2.2.2.39).

[1] https://sites.google.com/site/fullycapable/, posix_1003.1e-990310.pdf

Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
---
 man2/perf_event_open.2 | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
index 89d267c02..e9aab2ca1 100644
--- a/man2/perf_event_open.2
+++ b/man2/perf_event_open.2
@@ -98,6 +98,8 @@ when running on the specified CPU.
 .BR "pid == \-1" " and " "cpu >= 0"
 This measures all processes/threads on the specified CPU.
 This requires
+.B CAP_PERFMON
+or
 .B CAP_SYS_ADMIN
 capability or a
 .I /proc/sys/kernel/perf_event_paranoid
@@ -2920,6 +2922,8 @@ to hold the result.
 This allows attaching a Berkeley Packet Filter (BPF)
 program to an existing kprobe tracepoint event.
 You need
+.B CAP_PERFMON
+or
 .B CAP_SYS_ADMIN
 privileges to use this ioctl.
 .IP
@@ -2962,6 +2966,8 @@ have multiple events attached to a tracepoint.
 Querying this value on one tracepoint event returns the id
 of all BPF programs in all events attached to the tracepoint.
 You need
+.B CAP_PERFMON
+or
 .B CAP_SYS_ADMIN
 privileges to use this ioctl.
 .IP
@@ -3170,6 +3176,8 @@ it was expecting.
 .TP
 .B EACCES
 Returned when the requested event requires
+.B CAP_PERFMON
+or
 .B CAP_SYS_ADMIN
 permissions (or a more permissive perf_event paranoid setting).
 Some common cases where an unprivileged process
@@ -3291,6 +3299,8 @@ setting is specified.
 It can also happen, as with
 .BR EACCES ,
 when the requested event requires
+.B CAP_PERFMON
+or
 .B CAP_SYS_ADMIN
 permissions (or a more permissive perf_event paranoid setting).
 This includes setting a breakpoint on a kernel address,
@@ -3321,6 +3331,23 @@ The official way of knowing if
 support is enabled is checking
 for the existence of the file
 .IR /proc/sys/kernel/perf_event_paranoid .
+.PP
+.B CAP_PERFMON
+capability (since Linux X.Y) provides secure approach to
+performance monitoring and observability operations in a system
+according to the principal of least privilege (POSIX IEEE 1003.1e).
+Accessing system performance monitoring and observability operations
+using
+.B CAP_PERFMON
+capability singly, without the rest of
+.B CAP_SYS_ADMIN
+credentials, excludes chances to misuse the credentials and makes
+the operations more secure.
+.B CAP_SYS_ADMIN
+usage for secure system performance monitoring and observability
+is discouraged with respect to
+.B CAP_PERFMON
+capability.
 .SH BUGS
 The
 .B F_SETOWN_EX
-- 
2.20.1