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

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Message-ID: <ed6f63bd-5dcb-425d-60ee-311a68756bfe@gmail.com>
Date:   Sun, 23 Aug 2020 19:28:31 +0200
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.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: Re: [PATCH v1] perf_event_open.2: update the man page with
 CAP_PERFMON related information

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@...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

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