[PATCH bpf-next 1/2] bpf: Allow ringbuf memory to be used as map key

[Dave Marchevsky <davemarchevsky@xxxxxx>]

This patch adds support for the following pattern:

  struct some_data *data = bpf_ringbuf_reserve(&ringbuf, sizeof(struct some_data, 0));
  bpf_map_lookup_elem(&another_map, &data->some_field);
  bpf_ringbuf_submit(data);

Currently the verifier does not consider bpf_ringbuf_reserve's
PTR_TO_MEM ret type a valid key input to bpf_map_lookup_elem. Since
PTR_TO_MEM is by definition a valid region of memory, it is safe to use
it as a key for lookups.

Signed-off-by: Dave Marchevsky <davemarchevsky@xxxxxx>
---
 kernel/bpf/verifier.c                         |  2 +
 tools/testing/selftests/bpf/Makefile          |  8 ++-
 .../selftests/bpf/prog_tests/ringbuf.c        | 10 +++
 .../bpf/progs/test_ringbuf_map_key.c          | 69 +++++++++++++++++++
 4 files changed, 86 insertions(+), 3 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/test_ringbuf_map_key.c

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c259d734f863..d093618aed99 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5626,6 +5626,8 @@ static const struct bpf_reg_types map_key_value_types = {
 		PTR_TO_PACKET_META,
 		PTR_TO_MAP_KEY,
 		PTR_TO_MAP_VALUE,
+		PTR_TO_MEM,
+		PTR_TO_MEM | MEM_ALLOC,
 	},
 };
 
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 6cd327f1f216..231d9c1364c9 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -351,9 +351,11 @@ LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h		\
 		test_subskeleton.skel.h test_subskeleton_lib.skel.h	\
 		test_usdt.skel.h
 
-LSKELS := fentry_test.c fexit_test.c fexit_sleep.c \
-	test_ringbuf.c atomics.c trace_printk.c trace_vprintk.c \
-	map_ptr_kern.c core_kern.c core_kern_overflow.c
+LSKELS := fentry_test.c fexit_test.c fexit_sleep.c atomics.c 		\
+	trace_printk.c trace_vprintk.c map_ptr_kern.c 			\
+	core_kern.c core_kern_overflow.c test_ringbuf.c			\
+	test_ringbuf_map_key.c
+
 # Generate both light skeleton and libbpf skeleton for these
 LSKELS_EXTRA := test_ksyms_module.c test_ksyms_weak.c kfunc_call_test.c \
 	kfunc_call_test_subprog.c
diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
index 9a80fe8a6427..1cf458d1a179 100644
--- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
+++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
@@ -13,6 +13,7 @@
 #include <linux/perf_event.h>
 #include <linux/ring_buffer.h>
 #include "test_ringbuf.lskel.h"
+#include "test_ringbuf_map_key.lskel.h"
 
 #define EDONE 7777
 
@@ -297,3 +298,12 @@ void test_ringbuf(void)
 	ring_buffer__free(ringbuf);
 	test_ringbuf_lskel__destroy(skel);
 }
+
+void test_ringbuf_map_key(void)
+{
+	struct test_ringbuf_map_key_lskel *skel_map_key;
+
+	skel_map_key = test_ringbuf_map_key_lskel__open_and_load();
+	ASSERT_OK_PTR(skel_map_key, "test_ringbuf_map_key_lskel__open_and_load failed");
+	test_ringbuf_map_key_lskel__destroy(skel_map_key);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_ringbuf_map_key.c b/tools/testing/selftests/bpf/progs/test_ringbuf_map_key.c
new file mode 100644
index 000000000000..96a791a9762e
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_ringbuf_map_key.c
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+struct sample {
+	int pid;
+	int seq;
+	long value;
+	char comm[16];
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_RINGBUF);
+	__uint(max_entries, 4096);
+} ringbuf SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 1000);
+	__type(key, struct sample);
+	__type(value, int);
+} hash_map SEC(".maps");
+
+/* inputs */
+int pid = 0;
+long value = 0;
+long flags = 0;
+
+/* outputs */
+long total = 0;
+long dropped = 0;
+
+/* inner state */
+long seq = 0;
+
+SEC("fentry/" SYS_PREFIX "sys_getpgid")
+int test_ringbuf_mem_map_key(void *ctx)
+{
+	int cur_pid = bpf_get_current_pid_tgid() >> 32;
+	struct sample *sample;
+	int *lookup_val;
+	int zero = 0;
+
+	if (cur_pid != pid)
+		return 0;
+
+	sample = bpf_ringbuf_reserve(&ringbuf, sizeof(*sample), 0);
+	if (!sample) {
+		__sync_fetch_and_add(&dropped, 1);
+		return 0;
+	}
+
+	sample->pid = pid;
+	bpf_get_current_comm(sample->comm, sizeof(sample->comm));
+	sample->value = value;
+	sample->seq = seq++;
+
+	/* This prog is never run, successful load w/ below use of sample mem
+	 * as map key is considered success
+	 */
+	lookup_val = (int *)bpf_map_lookup_elem(&hash_map, sample);
+	bpf_ringbuf_submit(sample, 0);
+	return 0;
+}
-- 
2.30.2