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From: Stephen Smalley <sds@tycho.nsa.gov>
To: Alexey Budankov <alexey.budankov@linux.intel.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Song Liu <songliubraving@fb.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"joonas.lahtinen@linux.intel.com"
	<joonas.lahtinen@linux.intel.com>,
	Will Deacon <will.deacon@arm.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Stephane Eranian <eranian@google.com>,
	"james.bottomley@hansenpartnership.com"
	<james.bottomley@hansenpartnership.com>,
	Paul Mackerras <paulus@samba.org>, Jiri Olsa <jolsa@redhat.com>,
	Andi Kleen <ak@linux.intel.com>,
	Igor Lubashev <ilubashe@akamai.com>,
	James Morris <jmorris@namei.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Ingo Molnar <mingo@redhat.com>,
	oprofile-list@lists.sf.net, Serge Hallyn <serge@hallyn.com>,
	Robert Richter <rric@kernel.org>,
	"selinux@vger.kernel.org" <selinux@vger.kernel.org>,
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	<intel-gfx@lists.freedesktop.org>,
	"jani.nikula@linux.intel.com" <jani.nikula@linux.intel.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	"rodrigo.vivi@intel.com" <rodrigo.vivi@intel.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	"linux-parisc@vger.kernel.org" <linux-parisc@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Lionel Landwerlin <lionel.g.landwerlin@intel.com>,
	Andy Lutomirski <luto@amacapital.net>,
	"linux-perf-users@vger.kernel.org"
	<linux-perf-users@vger.kernel.org>,
	"linux-security-module@vger.kernel.org"
	<linux-security-module@vger.kernel.org>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH v5 01/10] capabilities: introduce CAP_PERFMON to kernel and user space
Date: Wed, 22 Jan 2020 09:07:32 -0500	[thread overview]
Message-ID: <d7213569-9578-7201-6106-f5ebc95bd6be@tycho.nsa.gov> (raw)
In-Reply-To: <63d9700f-231d-7973-5307-3e56a48c54cb@linux.intel.com>

On 1/22/20 5:45 AM, Alexey Budankov wrote:
> 
> 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@linux.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@linux.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.

I can live with that.  We just need to document that when you see both a 
CAP_PERFMON and a CAP_SYS_ADMIN audit message for a process, try only 
allowing CAP_PERFMON first and see if that resolves the issue.  We have 
a similar issue with CAP_DAC_READ_SEARCH versus CAP_DAC_OVERRIDE.

  reply	other threads:[~2020-01-22 14:14 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-20 11:18 [PATCH v5 0/10] Introduce CAP_PERFMON to secure system performance monitoring and observability Alexey Budankov
2020-01-20 11:23 ` [PATCH v5 01/10] capabilities: introduce CAP_PERFMON to kernel and user space Alexey Budankov
2020-01-21 14:43   ` Stephen Smalley
2020-01-21 17:30     ` Alexey Budankov
2020-01-21 17:55       ` Alexei Starovoitov
2020-01-21 18:27         ` Alexey Budankov
2020-01-22 10:45           ` Alexey Budankov
2020-01-22 14:07             ` Stephen Smalley [this message]
2020-01-22 14:25               ` Alexey Budankov
2020-02-06 18:03                 ` Alexey Budankov
2020-02-07 11:38                   ` Thomas Gleixner
2020-02-07 13:39                     ` Alexey Budankov
2020-02-20 13:05                       ` Alexey Budankov
2020-02-12  8:53               ` Alexey Budankov
2020-02-12 13:32                 ` Stephen Smalley
2020-02-12 13:53                   ` Alexey Budankov
2020-02-12 15:21                     ` Stephen Smalley
2020-02-12 15:45                       ` Stephen Smalley
2020-02-12 16:56                         ` Alexey Budankov
2020-02-12 17:09                           ` Stephen Smalley
2020-02-13  9:05                             ` Alexey Budankov
2020-02-12 16:16                       ` Alexey Budankov
2020-01-20 11:24 ` [PATCH v5 02/10] perf/core: open access to the core for CAP_PERFMON privileged process Alexey Budankov
2020-01-20 11:26 ` [PATCH v5 03/10] perf/core: open access to anon probes " Alexey Budankov
2020-01-20 11:27 ` [PATCH v5 04/10] perf tool: extend Perf tool with CAP_PERFMON capability support Alexey Budankov
2020-01-20 11:28 ` [PATCH v5 05/10] drm/i915/perf: open access for CAP_PERFMON privileged process Alexey Budankov
2020-01-20 11:29 ` [PATCH v5 06/10] trace/bpf_trace: " Alexey Budankov
2020-01-20 11:30 ` [PATCH v5 07/10] powerpc/perf: " Alexey Budankov
2020-01-22 11:02   ` Anju T Sudhakar
2020-01-20 11:31 ` [PATCH v5 08/10] parisc/perf: " Alexey Budankov
2020-01-20 11:32 ` [PATCH v5 09/10] drivers/perf: " Alexey Budankov
2020-01-20 11:33 ` [PATCH v5 10/10] drivers/oprofile: " Alexey Budankov

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