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    SubjectRe: [PATCH v5 01/10] capabilities: introduce CAP_PERFMON to kernel and user space
    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.
    >
    > 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.

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