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Subject[RFC 1/2] perf/pmu: Allow PMU providers to override system-wide security settings
Date
From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

To allow system administrators finer-grained control over security
settings, we add an optional pmu->is_privileged(pmu, event) callback
which is consulted when unprivileged system-wide uncore event collection
is disabled.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: linux-kernel@vger.kernel.org
Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
---
include/linux/perf_event.h | 6 ++++++
kernel/events/core.c | 12 +++++++++++-
2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 8e22f24ded6a..a93630cad6b9 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -446,6 +446,12 @@ struct pmu {
* Filter events for PMU-specific reasons.
*/
int (*filter_match) (struct perf_event *event); /* optional */
+
+ /*
+ * Returns true if the event needs CAP_SYS_ADMIN privilege in system-
+ * wide mode.
+ */
+ bool (*is_privileged) (struct perf_event *event); /* optional */
};

/**
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1811dd5aa2e2..adec28c879e8 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3847,6 +3847,16 @@ find_lively_task_by_vpid(pid_t vpid)
return task;
}

+static bool cpu_is_privileged(struct pmu *pmu, struct perf_event *event)
+{
+ bool privileged = perf_paranoid_cpu();
+
+ if (privileged && pmu->is_privileged)
+ privileged = pmu->is_privileged(event);
+
+ return privileged;
+}
+
/*
* Returns a matching context with refcount and pincount.
*/
@@ -3863,7 +3873,7 @@ find_get_context(struct pmu *pmu, struct task_struct *task,

if (!task) {
/* Must be root to operate on a CPU event: */
- if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
+ if (cpu_is_privileged(pmu, event) && !capable(CAP_SYS_ADMIN))
return ERR_PTR(-EACCES);

cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu);
--
2.14.1
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