[RFC PATCH 02/11] perf: Add PERF_PMU_CAP_IS_DEVICE flag

[Robert Bragg]

The PERF_PMU_CAP_IS_DEVICE flag provides pmu drivers a way to declare
that they only monitor device specific metrics and since they don't
monitor any cpu metrics then perf should bypass any cpu centric security
checks, as well as disallow cpu centric attributes.

Signed-off-by: Robert Bragg <robert at sixbynine.org>
---
 include/linux/perf_event.h |  1 +
 kernel/events/core.c       | 39 +++++++++++++++++++++++++++++++++------
 2 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 2b62198..1af35b4 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -166,6 +166,7 @@ struct perf_event;
  * pmu::capabilities flags
  */
 #define PERF_PMU_CAP_NO_INTERRUPT		0x01
+#define PERF_PMU_CAP_IS_DEVICE			0x02
 
 /**
  * struct pmu - generic performance monitoring unit
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 38c240c..7218b01 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3330,7 +3330,8 @@ find_get_context(struct pmu *pmu, struct task_struct *task, int cpu)
 
 	if (!task) {
 		/* Must be root to operate on a CPU event: */
-		if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
+		if (!(pmu->capabilities & PERF_PMU_CAP_IS_DEVICE) &&
+		    perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
 			return ERR_PTR(-EACCES);
 
 		/*
@@ -7475,11 +7476,6 @@ SYSCALL_DEFINE5(perf_event_open,
 	if (err)
 		return err;
 
-	if (!attr.exclude_kernel) {
-		if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
-			return -EACCES;
-	}
-
 	if (attr.freq) {
 		if (attr.sample_freq > sysctl_perf_event_sample_rate)
 			return -EINVAL;
@@ -7538,6 +7534,37 @@ SYSCALL_DEFINE5(perf_event_open,
 		goto err_cpus;
 	}
 
+	if (event->pmu->capabilities & PERF_PMU_CAP_IS_DEVICE) {
+
+		/* Don't allow cpu centric attributes... */
+		if (event->attr.exclude_user ||
+		    event->attr.exclude_callchain_user ||
+		    event->attr.exclude_kernel ||
+		    event->attr.exclude_callchain_kernel ||
+		    event->attr.exclude_hv ||
+		    event->attr.exclude_idle ||
+		    event->attr.exclude_host ||
+		    event->attr.exclude_guest ||
+		    event->attr.mmap ||
+		    event->attr.comm ||
+		    event->attr.task)
+			return -EINVAL;
+
+		if (attr.sample_type &
+		    (PERF_SAMPLE_IP |
+		     PERF_SAMPLE_TID |
+		     PERF_SAMPLE_ADDR |
+		     PERF_SAMPLE_CALLCHAIN |
+		     PERF_SAMPLE_CPU |
+		     PERF_SAMPLE_BRANCH_STACK |
+		     PERF_SAMPLE_REGS_USER |
+		     PERF_SAMPLE_STACK_USER))
+			return -EINVAL;
+	} else if (!attr.exclude_kernel) {
+		if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
+			return -EACCES;
+	}
+
 	if (flags & PERF_FLAG_PID_CGROUP) {
 		err = perf_cgroup_connect(pid, event, &attr, group_leader);
 		if (err) {
-- 
2.3.2