Re: [PATCH v1] perf_event_open.2: update the man page with CAP_PERFMON related information

From: Michael Kerrisk (man-pages)
Date: Sun Aug 23 2020 - 13:28:43 EST


Hello Alexey,

Could you look at the question below and update the patch.

On 2/17/20 9:18 AM, Alexey Budankov wrote:

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 | 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

What's the version?

+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

I think that wording like "using CAP_PERFMON rather than the much
more powerful CAP_SYS_ADMIN..."

+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

Thanks,

Michael