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Message-ID: <63d9700f-231d-7973-5307-3e56a48c54cb@linux.intel.com>
Date: Wed, 22 Jan 2020 13:45:45 +0300
From: Alexey Budankov <alexey.budankov@...ux.intel.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>,
Stephen Smalley <sds@...ho.nsa.gov>
Cc: 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>,
"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
Michael Ellerman <mpe@...erman.id.au>,
"james.bottomley@...senpartnership.com"
<james.bottomley@...senpartnership.com>,
Serge Hallyn <serge@...lyn.com>,
James Morris <jmorris@...ei.org>,
Will Deacon <will.deacon@....com>,
Mark Rutland <mark.rutland@....com>,
Robert Richter <rric@...nel.org>,
Alexei Starovoitov <ast@...nel.org>,
Jiri Olsa <jolsa@...hat.com>, Andi Kleen <ak@...ux.intel.com>,
Stephane Eranian <eranian@...gle.com>,
Igor Lubashev <ilubashe@...mai.com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Namhyung Kim <namhyung@...nel.org>,
Song Liu <songliubraving@...com>,
Lionel Landwerlin <lionel.g.landwerlin@...el.com>,
Thomas Gleixner <tglx@...utronix.de>,
linux-kernel <linux-kernel@...r.kernel.org>,
"linux-security-module@...r.kernel.org"
<linux-security-module@...r.kernel.org>,
"selinux@...r.kernel.org" <selinux@...r.kernel.org>,
"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
"linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
"linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
oprofile-list@...ts.sf.net, Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH v5 01/10] capabilities: introduce CAP_PERFMON to kernel
and user space
On 21.01.2020 21:27, Alexey Budankov wrote:
>
> On 21.01.2020 20:55, Alexei Starovoitov wrote:
>> On Tue, Jan 21, 2020 at 9:31 AM Alexey Budankov
>> <alexey.budankov@...ux.intel.com> wrote:
>>>
>>>
>>> On 21.01.2020 17:43, Stephen Smalley wrote:
>>>> On 1/20/20 6:23 AM, Alexey Budankov wrote:
>>>>>
>>>>> Introduce CAP_PERFMON capability designed to secure system performance
>>>>> monitoring and observability operations so that CAP_PERFMON would assist
>>>>> CAP_SYS_ADMIN capability in its governing role for perf_events, i915_perf
>>>>> and other performance monitoring and observability subsystems.
>>>>>
>>>>> CAP_PERFMON intends to harden system security and integrity during system
>>>>> performance monitoring and observability operations by decreasing attack
>>>>> surface that is available to a CAP_SYS_ADMIN privileged process [1].
>>>>> Providing access to system performance monitoring and observability
>>>>> operations under CAP_PERFMON capability singly, without the rest of
>>>>> CAP_SYS_ADMIN credentials, excludes chances to misuse the credentials and
>>>>> makes operation more secure.
>>>>>
>>>>> CAP_PERFMON intends to take over CAP_SYS_ADMIN credentials related to
>>>>> system performance monitoring and observability operations and balance
>>>>> amount of CAP_SYS_ADMIN credentials following the recommendations in the
>>>>> capabilities man page [1] for CAP_SYS_ADMIN: "Note: this capability is
>>>>> overloaded; see Notes to kernel developers, below."
>>>>>
>>>>> Although the software running under CAP_PERFMON can not ensure avoidance
>>>>> of related hardware issues, the software can still mitigate these issues
>>>>> following the official embargoed hardware issues mitigation procedure [2].
>>>>> The bugs in the software itself could be fixed following the standard
>>>>> kernel development process [3] to maintain and harden security of system
>>>>> performance monitoring and observability operations.
>>>>>
>>>>> [1] http://man7.org/linux/man-pages/man7/capabilities.7.html
>>>>> [2] https://www.kernel.org/doc/html/latest/process/embargoed-hardware-issues.html
>>>>> [3] https://www.kernel.org/doc/html/latest/admin-guide/security-bugs.html
>>>>>
>>>>> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
>>>>> ---
>>>>> include/linux/capability.h | 12 ++++++++++++
>>>>> include/uapi/linux/capability.h | 8 +++++++-
>>>>> security/selinux/include/classmap.h | 4 ++--
>>>>> 3 files changed, 21 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/include/linux/capability.h b/include/linux/capability.h
>>>>> index ecce0f43c73a..8784969d91e1 100644
>>>>> --- a/include/linux/capability.h
>>>>> +++ b/include/linux/capability.h
>>>>> @@ -251,6 +251,18 @@ extern bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct
>>>>> extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap);
>>>>> extern bool file_ns_capable(const struct file *file, struct user_namespace *ns, int cap);
>>>>> extern bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns);
>>>>> +static inline bool perfmon_capable(void)
>>>>> +{
>>>>> + struct user_namespace *ns = &init_user_ns;
>>>>> +
>>>>> + if (ns_capable_noaudit(ns, CAP_PERFMON))
>>>>> + return ns_capable(ns, CAP_PERFMON);
>>>>> +
>>>>> + if (ns_capable_noaudit(ns, CAP_SYS_ADMIN))
>>>>> + return ns_capable(ns, CAP_SYS_ADMIN);
>>>>> +
>>>>> + return false;
>>>>> +}
>>>>
>>>> Why _noaudit()? Normally only used when a permission failure is non-fatal to the operation. Otherwise, we want the audit message.
So far so good, I suggest using the simplest version for v6:
static inline bool perfmon_capable(void)
{
return capable(CAP_PERFMON) || capable(CAP_SYS_ADMIN);
}
It keeps the implementation simple and readable. The implementation is more
performant in the sense of calling the API - one capable() call for CAP_PERFMON
privileged process.
Yes, it bloats audit log for CAP_SYS_ADMIN privileged and unprivileged processes,
but this bloating also advertises and leverages using more secure CAP_PERFMON
based approach to use perf_event_open system call.
~Alexey
>>>
>>> Some of ideas from v4 review.
>>
>> well, in the requested changes form v4 I wrote:
>> return capable(CAP_PERFMON);
>> instead of
>> return false;
>
> Aww, indeed. I was concerning exactly about it when updating the patch
> and simply put false, missing the fact that capable() also logs.
>
> I suppose the idea is originally from here [1].
> BTW, Has it already seen any _more optimal_ implementation?
> Anyway, original or optimized version could be reused for CAP_PERFMON.
>
> ~Alexey
>
> [1] https://patchwork.ozlabs.org/patch/1159243/
>
>>
>> That's what Andy suggested earlier for CAP_BPF.
>> I think that should resolve Stephen's concern.
>>
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