[PATCH v2] perf_event_open.2: update the man page with CAP_PERFMON related information

From: Alexey Budankov
Date: Tue Oct 27 2020 - 12:52:40 EST



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@xxxxxxxxxxxxxxx>
---
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