bpf, trace: add BPF_F_CURRENT_CPU flag for bpf_perf_event_read

Follow-up commit to 1e33759c ("bpf, trace: add BPF_F_CURRENT_CPU
flag for bpf_perf_event_output") to add the same functionality into
bpf_perf_event_read() helper. The split of index into flags and index
component is also safe here, since such large maps are rejected during
map allocation time.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/bpf.h

@@ -347,7 +347,7 @@ enum bpf_func_id {
 #define BPF_F_ZERO_CSUM_TX		(1ULL << 1)
 #define BPF_F_DONT_FRAGMENT		(1ULL << 2)
 
-/* BPF_FUNC_perf_event_output flags. */
+/* BPF_FUNC_perf_event_output and BPF_FUNC_perf_event_read flags. */
 #define BPF_F_INDEX_MASK		0xffffffffULL
 #define BPF_F_CURRENT_CPU		BPF_F_INDEX_MASK
 

kernel/trace/bpf_trace.c

@@ -188,13 +188,19 @@ const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
 	return &bpf_trace_printk_proto;
 }
 
-static u64 bpf_perf_event_read(u64 r1, u64 index, u64 r3, u64 r4, u64 r5)
+static u64 bpf_perf_event_read(u64 r1, u64 flags, u64 r3, u64 r4, u64 r5)
 {
 	struct bpf_map *map = (struct bpf_map *) (unsigned long) r1;
 	struct bpf_array *array = container_of(map, struct bpf_array, map);
+	unsigned int cpu = smp_processor_id();
+	u64 index = flags & BPF_F_INDEX_MASK;
 	struct bpf_event_entry *ee;
 	struct perf_event *event;
 
+	if (unlikely(flags & ~(BPF_F_INDEX_MASK)))
+		return -EINVAL;
+	if (index == BPF_F_CURRENT_CPU)
+		index = cpu;
 	if (unlikely(index >= array->map.max_entries))
 		return -E2BIG;
 
@@ -208,8 +214,7 @@ static u64 bpf_perf_event_read(u64 r1, u64 index, u64 r3, u64 r4, u64 r5)
 		return -EINVAL;
 
 	/* make sure event is local and doesn't have pmu::count */
-	if (event->oncpu != smp_processor_id() ||
-	    event->pmu->count)
+	if (unlikely(event->oncpu != cpu || event->pmu->count))
 		return -EINVAL;
 
 	/*