RE: [PATCH v2 2/7] perf/core: open access for CAP_SYS_PERFMON privileged process

From: "Lubashev, Igor" <ilubashe@akamai.com>
To: Alexey Budankov <alexey.budankov@linux.intel.com>,
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	Arnaldo Carvalho de Melo <acme@kernel.org>,
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Subject: RE: [PATCH v2 2/7] perf/core: open access for CAP_SYS_PERFMON privileged process
Date: Mon, 16 Dec 2019 16:12:50 +0000	[thread overview]
Message-ID: <9316a1ab21f6441eb2b421acb818a2a1@ustx2ex-dag1mb6.msg.corp.akamai.com> (raw)
In-Reply-To: <fd6ffb43-ed43-14cd-b286-6ab4b199155b@linux.intel.com>

On Mon, Dec 16, 2019 at 2:15 AM, Alexey Budankov <alexey.budankov@linux.intel.com> wrote:
> 
> Open access to perf_events monitoring for CAP_SYS_PERFMON privileged
> processes.
> For backward compatibility reasons access to perf_events subsystem remains
> open for CAP_SYS_ADMIN privileged processes but CAP_SYS_ADMIN usage
> for secure perf_events monitoring is discouraged with respect to
> CAP_SYS_PERFMON capability.
> 
> Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
> ---
>  include/linux/perf_event.h | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index
> 34c7c6910026..52313d2cc343 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1285,7 +1285,8 @@ static inline int perf_is_paranoid(void)
> 
>  static inline int perf_allow_kernel(struct perf_event_attr *attr)  {
> -	if (sysctl_perf_event_paranoid > 1 && !capable(CAP_SYS_ADMIN))
> +	if (sysctl_perf_event_paranoid > 1 &&
> +	   !(capable(CAP_SYS_PERFMON) || capable(CAP_SYS_ADMIN)))
>  		return -EACCES;
> 
>  	return security_perf_event_open(attr, PERF_SECURITY_KERNEL); @@
> -1293,7 +1294,8 @@ static inline int perf_allow_kernel(struct
> perf_event_attr *attr)
> 
>  static inline int perf_allow_cpu(struct perf_event_attr *attr)  {
> -	if (sysctl_perf_event_paranoid > 0 && !capable(CAP_SYS_ADMIN))
> +	if (sysctl_perf_event_paranoid > 0 &&
> +	    !(capable(CAP_SYS_PERFMON) || capable(CAP_SYS_ADMIN)))
>  		return -EACCES;
> 
>  	return security_perf_event_open(attr, PERF_SECURITY_CPU); @@ -
> 1301,7 +1303,8 @@ static inline int perf_allow_cpu(struct perf_event_attr
> *attr)
> 
>  static inline int perf_allow_tracepoint(struct perf_event_attr *attr)  {
> -	if (sysctl_perf_event_paranoid > -1 && !capable(CAP_SYS_ADMIN))
> +	if (sysctl_perf_event_paranoid > -1 &&
> +	    !(capable(CAP_SYS_PERFMON) || capable(CAP_SYS_ADMIN)))
>  		return -EPERM;
> 
>  	return security_perf_event_open(attr, PERF_SECURITY_TRACEPOINT);
> --
> 2.20.1

Thanks.  I like the idea of CAP_SYS_PERFMON that does not require CAP_SYS_ADMIN.  It makes granting users ability to run perf a bit safer.

I see a lot of "(capable(CAP_SYS_PERFMON) || capable(CAP_SYS_ADMIN)" constructs now.  Maybe wrapping it in an " inline bool perfmon_capable()" defined somewhere (like in /include/linux/capability.h)?

- Igor