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

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Message-ID: <3f2ac76c-6108-7769-4b99-a7a2da31af3d@linux.intel.com>
Date:   Mon, 16 Dec 2019 19:33:48 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     "Lubashev, Igor" <ilubashe@...mai.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 16.12.2019 19:12, Lubashev, Igor wrote:
> 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)?

Yes, it makes sense.

Thanks,
Alexey

> 
> - Igor
>