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Reply-To: mtk.manpages@gmail.com
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Date:   Tue, 27 Oct 2020 10:25:26 +0100
Message-ID: <CAKgNAkirXKh6VocM7-gwvC1CoDgqV7NjpU5OSVvXJX9mwiNnBg@mail.gmail.com>
Subject: Re: [PATCH v1] perf_event_open.2: update the man page with
 CAP_PERFMON related information
To:     Alexey Budankov <alexey.budankov@linux.intel.com>
Cc:     linux-man <linux-man@vger.kernel.org>,
        James Morris <jmorris@namei.org>,
        Serge Hallyn <serge@hallyn.com>,
        Stephen Smalley <sds@tycho.nsa.gov>,
        Peter Zijlstra <peterz@infradead.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andi Kleen <ak@linux.intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Michael Kerrisk <mtk.manpages@gmail.com>
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Hi Alexei,

Would you be able to refresh this patch and resend please?

Thnks,

Michael

On Mon, 24 Aug 2020 at 22:17, Alexey Budankov
<alexey.budankov@linux.intel.com> wrote:
>
> Hi Michael,
>
> On 23.08.2020 20:28, Michael Kerrisk (man-pages) wrote:
> > 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@linux.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?
>
> It's since Linux 5.8 .
>
> >
> >> +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..."
>
> Sounds good to me like this, or similar:
>
> "Accessing system performance monitoring and observability operations
>  using CAP_PERFMON rather than the much more powerful CAP_SYS_ADMIN
>  excludes chances to misuse credentials and makes operations more
>  secure."
>
> >
> >> +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
> >
>
> Thanks,
> Alexei
>
> P.S.
> I am on vacations till 08/31.
> Please expect delay in response.
>


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/