bpf: mark a NULL kfunc argument precisegrafted

check_kfunc_arg() allows bpf_register_is_null() for nullable arguments
w/o marking the underlying scalar register precise. Hence a checkpoint
created on such a path would prune against arbitrary scalar value.

Fixes: 3bda08b63670 ("bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)")
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260904-register-is-null-precise-fixes-v1-5-0f5a360ff15d@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 27 insertions, 0 deletions

diff --git a/tools/perf/util/btf.c b/tools/perf/util/btf.c
new file mode 100644
index 000000000..50d98f3e8
--- /dev/null
+++ b/tools/perf/util/btf.c
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Arnaldo Carvalho de Melo <acme@redhat.com>
+ *
+ * Copyright (C) 2024, Red Hat, Inc
+ */
+
+#include <bpf/btf.h>
+#include <util/btf.h>
+#include <string.h>
+
+const struct btf_member *__btf_type__find_member_by_name(struct btf *btf,
+							 int type_id, const char *member_name)
+{
+	const struct btf_type *t = btf__type_by_id(btf, type_id);
+	const struct btf_member *m;
+	u32 i;
+
+	for (i = 0, m = btf_members(t); i < btf_vlen(t); i++, m++) {
+		const char *current_member_name = btf__name_by_offset(btf, m->name_off);
+
+		if (!strcmp(current_member_name, member_name))
+			return m;
+	}
+
+	return NULL;
+}