linux-kernel - RE: [PATCH v2 2/7] perf/core: open access for CAP_SYS

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Message-ID: <9316a1ab21f6441eb2b421acb818a2a1@ustx2ex-dag1mb6.msg.corp.akamai.com>
Date:   Mon, 16 Dec 2019 16:12:50 +0000
From:   "Lubashev, Igor" <ilubashe@...mai.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        "Ingo Molnar" <mingo@...hat.com>,
        "jani.nikula@...ux.intel.com" <jani.nikula@...ux.intel.com>,
        "joonas.lahtinen@...ux.intel.com" <joonas.lahtinen@...ux.intel.com>,
        "rodrigo.vivi@...el.com" <rodrigo.vivi@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        "james.bottomley@...senpartnership.com" 
        <james.bottomley@...senpartnership.com>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        "serge@...lyn.com" <serge@...lyn.com>,
        James Morris <jmorris@...ei.org>
CC:     Jiri Olsa <jolsa@...hat.com>, Andi Kleen <ak@...ux.intel.com>,
        "Stephane Eranian" <eranian@...gle.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "selinux@...r.kernel.org" <selinux@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "bgregg@...flix.com" <bgregg@...flix.com>,
        Song Liu <songliubraving@...com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: RE: [PATCH v2 2/7] perf/core: open access for CAP_SYS_PERFMON
 privileged process

On Mon, Dec 16, 2019 at 2:15 AM, Alexey Budankov <alexey.budankov@...ux.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@...ux.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