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.
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