linux-kernel - [PATCH v2] perf_event_open.2: update the man page with CAP

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Message-ID: <33c10554-c0ee-9e46-2946-67a9deac6752@linux.intel.com>
Date:   Tue, 27 Oct 2020 19:48:25 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-man <linux-man@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH v2] 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 | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
index 4827a359d..9810bc554 100644
--- a/man2/perf_event_open.2
+++ b/man2/perf_event_open.2
@@ -97,6 +97,8 @@ 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
+(since Linux 5.8) or
 .B CAP_SYS_ADMIN
 capability or a
 .I /proc/sys/kernel/perf_event_paranoid
@@ -108,9 +110,11 @@ This setting is invalid and will return an error.
 When
 .I pid
 is greater than zero, permission to perform this system call
-is governed by a ptrace access mode
+is governed by
+.B CAP_PERFMON
+(since Linux 5.9) and a ptrace access mode
 .B PTRACE_MODE_READ_REALCREDS
-check; see
+check on older Linux versions; see
 .BR ptrace (2).
 .PP
 The
@@ -2925,6 +2929,8 @@ to hold the result.
 This allows attaching a Berkeley Packet Filter (BPF)
 program to an existing kprobe tracepoint event.
 You need
+.B CAP_PERFMON
+(since Linux 5.8) or
 .B CAP_SYS_ADMIN
 privileges to use this ioctl.
 .IP
@@ -2967,6 +2973,8 @@ 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
+(since Linux 5.8) or
 .B CAP_SYS_ADMIN
 privileges to use this ioctl.
 .IP
@@ -3175,6 +3183,8 @@ it was expecting.
 .TP
 .B EACCES
 Returned when the requested event requires
+.B CAP_PERFMON
+(since Linux 5.8) or
 .B CAP_SYS_ADMIN
 permissions (or a more permissive perf_event paranoid setting).
 Some common cases where an unprivileged process
@@ -3296,6 +3306,8 @@ setting is specified.
 It can also happen, as with
 .BR EACCES ,
 when the requested event requires
+.B CAP_PERFMON
+(since Linux 5.8) or
 .B CAP_SYS_ADMIN
 permissions (or a more permissive perf_event paranoid setting).
 This includes setting a breakpoint on a kernel address,
@@ -3326,6 +3338,22 @@ 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 5.8) 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
+rather than the much more powerful
+.B CAP_SYS_ADMIN
+excludes chances to misuse credentials and makes 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
-- 
2.24.1