[PATCH bpf v1 8/8] selftests/bpf: Check callback map value lock identity

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Add a verifier test which retains a map value from an outer callback and
then acquires a lock through an inner callback value before attempting to
release the outer value's lock. Both values can denote different elements,
so the verifier must reject the mismatched unlock.

Keep a nested same-element lock/unlock program as a positive control. This
ensures assigning fresh identities to callback map values does not reject
balanced locking through one callback argument.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 .../selftests/bpf/prog_tests/verifier.c       |  2 +
 .../bpf/progs/verifier_callback_lock.c        | 73 +++++++++++++++++++
 2 files changed, 75 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/verifier_callback_lock.c

diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c
index 64ac49ad67e6..5c572dd725e7 100644
--- a/tools/testing/selftests/bpf/prog_tests/verifier.c
+++ b/tools/testing/selftests/bpf/prog_tests/verifier.c
@@ -25,6 +25,7 @@
 #include "verifier_btf_ctx_access.skel.h"
 #include "verifier_btf_unreliable_prog.skel.h"
 #include "verifier_call_large_imm.skel.h"
+#include "verifier_callback_lock.skel.h"
 #include "verifier_cfg.skel.h"
 #include "verifier_cgroup_inv_retcode.skel.h"
 #include "verifier_cgroup_skb.skel.h"
@@ -188,6 +189,7 @@ void test_verifier_bswap(void)                { RUN(verifier_bswap); }
 void test_verifier_btf_ctx_access(void)       { RUN(verifier_btf_ctx_access); }
 void test_verifier_btf_unreliable_prog(void)  { RUN(verifier_btf_unreliable_prog); }
 void test_verifier_call_large_imm(void)       { RUN(verifier_call_large_imm); }
+void test_verifier_callback_lock(void)        { RUN(verifier_callback_lock); }
 void test_verifier_cfg(void)                  { RUN(verifier_cfg); }
 void test_verifier_cgroup_inv_retcode(void)   { RUN(verifier_cgroup_inv_retcode); }
 void test_verifier_cgroup_skb(void)           { RUN(verifier_cgroup_skb); }
diff --git a/tools/testing/selftests/bpf/progs/verifier_callback_lock.c b/tools/testing/selftests/bpf/progs/verifier_callback_lock.c
new file mode 100644
index 000000000000..ee09dd66f467
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/verifier_callback_lock.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+struct bpf_map;
+
+struct lock_value {
+	struct bpf_spin_lock lock;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 2);
+	__type(key, int);
+	__type(value, struct lock_value);
+} lock_map SEC(".maps");
+
+struct callback_ctx {
+	struct lock_value *value;
+};
+
+static long lock_different_value(struct bpf_map *map, int *key,
+				 struct lock_value *value, struct callback_ctx *ctx)
+{
+	bpf_spin_lock(&value->lock);
+	bpf_spin_unlock(&ctx->value->lock);
+	return 0;
+}
+
+static long nest_lock_different_value(struct bpf_map *map, int *key,
+				      struct lock_value *value, void *data)
+{
+	struct callback_ctx ctx = { .value = value };
+
+	bpf_for_each_map_elem(&lock_map, lock_different_value, &ctx, 0);
+	return 0;
+}
+
+SEC("?tc")
+__description("callback map value has a distinct lock identity")
+__failure __msg("bpf_spin_unlock of different lock")
+int callback_value_lock_identity(void *ctx)
+{
+	bpf_for_each_map_elem(&lock_map, nest_lock_different_value, NULL, 0);
+	return 0;
+}
+
+static long lock_same_value(struct bpf_map *map, int *key,
+			    struct lock_value *value, void *data)
+{
+	bpf_spin_lock(&value->lock);
+	bpf_spin_unlock(&value->lock);
+	return 0;
+}
+
+static long nest_lock_same_value(struct bpf_map *map, int *key,
+				 struct lock_value *value, void *data)
+{
+	bpf_for_each_map_elem(&lock_map, lock_same_value, NULL, 0);
+	return 0;
+}
+
+SEC("?tc")
+__description("nested callback can lock its own map value")
+__success
+int callback_value_lock_identity_same(void *ctx)
+{
+	bpf_for_each_map_elem(&lock_map, nest_lock_same_value, NULL, 0);
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.53.0