From: Stephen Smalley <sds@tycho.nsa.gov>
To: Andi Kleen <ak@linux.intel.com>,
Casey Schaufler <casey@schaufler-ca.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Jiri Olsa <jolsa@redhat.com>,
elena.reshetova@intel.com,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jann Horn <jannh@google.com>, Kees Cook <keescook@chromium.org>,
Stephane Eranian <eranian@google.com>,
Namhyung Kim <namhyung@kernel.org>,
linux-security-module@vger.kernel.org, selinux@vger.kernel.org,
linux-kernel <linux-kernel@vger.kernel.org>,
"Serge E. Hallyn" <serge@hallyn.com>,
James Morris <jmorris@namei.org>
Subject: Re: [PATCH v1 0/3] Introduce CAP_SYS_PERFMON capability for secure Perf users groups
Date: Thu, 12 Dec 2019 09:24:25 -0500 [thread overview]
Message-ID: <d2095e4a-261b-b561-2a2c-cf00fd416503@tycho.nsa.gov> (raw)
In-Reply-To: <20191211203648.GA862919@tassilo.jf.intel.com>
On 12/11/19 3:36 PM, Andi Kleen wrote:
>>> In this circumstances CAP_SYS_PERFMON looks like smart balanced advancement that
>>> trade-offs between perf_events subsystem extensions, required level of control
>>> and configurability of perf_events, existing users adoption effort, and it brings
>>> security hardening benefits of decreasing attack surface for the existing users
>>> and use cases.
>>
>> I'm not 100% opposed to CAP_SYS_PERFMON. I am 100% opposed to new capabilities
>> that have a single use. Surely there are other CAP_SYS_ADMIN users that [cs]ould
>> be converted to CAP_SYS_PERFMON as well. If there is a class of system performance
>> privileged operations, say a dozen or so, you may have a viable argument.
>
> perf events is not a single use. It has a bazillion of sub functionalities,
> including hardware tracing, software tracing, pmu counters, software counters,
> uncore counters, break points and various other stuff in its PMU drivers.
>
> See it more as a whole quite heterogenous driver subsystem.
>
> I guess CAP_SYS_PERFMON is not a good name because perf is much more
> than just Perfmon. Perhaps call it CAP_SYS_PERF_EVENTS
That seems misleading since it isn't being checked for all perf_events
operations IIUC (CAP_SYS_ADMIN is still required for some?) and it is
even more specialized than CAP_SYS_PERFMON, making it less likely that
we could ever use this capability as a check for other kernel
performance monitoring facilities beyond perf_events.
I'm not as opposed to fine-grained capabilities as Casey is but I do
recognize that there are a limited number of available bits (although we
do have a fair number of unused ones currently given the extension to
64-bits) and that it would be easy to consume them all if we allocated
one for every kernel feature. That said, this might be a sufficiently
important use case to justify it.
Obviously I'd encourage you to consider leveraging SELinux as well but I
understand that you are looking for a solution that doesn't depend on a
distro using a particular LSM or a particular policy. I will note that
SELinux doesn't suffer from the limited bits problem because one can
always define a new SELinux security class with its own access vector
permissions bitmap, as has been done for the recently added LSM/SELinux
perf_event hooks.
I don't know who actually gets to decide when/if a new capability is
allocated. Maybe Serge and/or James as capabilities and LSM maintainers.
I have no objections to these patches from a SELinux POV.
next prev parent reply other threads:[~2019-12-12 14:24 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-05 16:15 [PATCH v1 0/3] Introduce CAP_SYS_PERFMON capability for secure Perf users groups Alexey Budankov
2019-12-05 16:19 ` [PATCH v1 1/3] capabilities: introduce CAP_SYS_PERFMON to kernel and user space Alexey Budankov
2019-12-05 16:21 ` [PATCH v1 2/3] perf/core: apply CAP_SYS_PERFMON to CPUs and kernel monitoring Alexey Budankov
2019-12-05 16:22 ` [PATCH v1 3/3] perf tool: extend Perf tool with CAP_SYS_PERFMON support Alexey Budankov
2019-12-05 16:49 ` [PATCH v1 0/3] Introduce CAP_SYS_PERFMON capability for secure Perf users groups Casey Schaufler
2019-12-05 17:05 ` Alexey Budankov
2019-12-05 17:33 ` Casey Schaufler
2019-12-05 18:11 ` Andi Kleen
2019-12-05 18:37 ` Alexey Budankov
2019-12-11 10:52 ` Alexey Budankov
2019-12-11 15:24 ` Peter Zijlstra
2019-12-11 17:00 ` Alexey Budankov
2019-12-11 18:09 ` Casey Schaufler
2019-12-11 20:36 ` Andi Kleen
2019-12-11 21:25 ` Casey Schaufler
2019-12-12 14:24 ` Stephen Smalley [this message]
2019-12-15 11:53 ` Alexey Budankov
2019-12-11 19:04 ` Stephane Eranian
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