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. ~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. >>
