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. > > Some of ideas from v4 review. well, in the requested changes form v4 I wrote: return capable(CAP_PERFMON); instead of return false; That's what Andy suggested earlier for CAP_BPF. I think that should resolve Stephen's concern.
