[RFC PATCH 2/3] perf: Add PERF_PMU_CAP_IS_DEVICE flag

[Robert Bragg <robert@sixbynine.org>]

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@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 707617a..e1e0153 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -170,6 +170,7 @@ 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 9449180..3ddb157 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3131,7 +3131,8 @@ 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);
 
 		/*
@@ -7091,11 +7092,6 @@ 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;
@@ -7154,6 +7150,37 @@ 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) {
-- 
2.1.2