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Date: Wed, 22 Jan 2020 09:07:32 -0500 From: Stephen Smalley <sds@...ho.nsa.gov> To: Alexey Budankov <alexey.budankov@...ux.intel.com>, Alexei Starovoitov <alexei.starovoitov@...il.com> 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 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@...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. 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.
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