On 22.01.2020 17:07, Stephen Smalley wrote: > 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@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx> >>>>>>> --- >>>>>>> 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. perf security [1] document can be updated, at least, to align and document this audit logging specifics. ~Alexey [1] https://www.kernel.org/doc/html/latest/admin-guide/perf-security.html
