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.
