On 27.10.2020 19:57, Michael Kerrisk (man-pages) wrote:
> Hello Alexey,
>
> On 10/27/20 5:48 PM, 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 <[email protected]>
>
> Thanks for this. I've applied. I have a few questions/comments below.
>
>> ---
>> 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
>
> I want to check: did you really mean 5.9 here? (Everywhere else,
> 5.8 is mentioned, but perhaps this change came in the next kernel
> version.)
Yes, it is not a typo. This thing was merged into v5.9.
Thanks,
Alexei
>
>> .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.
>
> Thank you for adding the above piece. That point of course
> really needs to be emphasized!
>
> Thanks,
>
> Michael
>
>
On Tue, 27 Oct 2020 at 18:10, Alexey Budankov
<[email protected]> wrote:
>
>
> On 27.10.2020 19:57, Michael Kerrisk (man-pages) wrote:
> > Hello Alexey,
> >
> > On 10/27/20 5:48 PM, 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 <[email protected]>
> >
> > Thanks for this. I've applied. I have a few questions/comments below.
> >
> >> ---
> >> 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
> >
> > I want to check: did you really mean 5.9 here? (Everywhere else,
> > 5.8 is mentioned, but perhaps this change came in the next kernel
> > version.)
>
> Yes, it is not a typo. This thing was merged into v5.9.
>
> Thanks,
> Alexei
Thanks, Alexei!
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/