[PATCH bpf-next 09/25] bpf: tracing: add support to record and check the accessed args

[Menglong Dong <menglong8.dong@gmail.com>]

In this commit, we add the 'accessed_args' field to struct bpf_prog_aux,
which is used to record the accessed index of the function args in
btf_ctx_access().

Meanwhile, we add the function btf_check_func_part_match() to compare the
accessed function args of two function prototype. This function will be
used in the following commit.

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
---
 include/linux/bpf.h |   4 ++
 kernel/bpf/btf.c    | 108 +++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 110 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 7527399bab5b..abf504e95ff2 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1601,6 +1601,7 @@ struct bpf_prog_aux {
 	const struct btf_type *attach_func_proto;
 	/* function name for valid attach_btf_id */
 	const char *attach_func_name;
+	u64 accessed_args;
 	struct bpf_prog **func;
 	void *jit_data; /* JIT specific data. arch dependent */
 	struct bpf_jit_poke_descriptor *poke_tab;
@@ -2779,6 +2780,9 @@ struct bpf_reg_state;
 int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog);
 int btf_check_type_match(struct bpf_verifier_log *log, const struct bpf_prog *prog,
 			 struct btf *btf, const struct btf_type *t);
+int btf_check_func_part_match(struct btf *btf1, const struct btf_type *t1,
+			      struct btf *btf2, const struct btf_type *t2,
+			      u64 func_args);
 const char *btf_find_decl_tag_value(const struct btf *btf, const struct btf_type *pt,
 				    int comp_idx, const char *tag_key);
 int btf_find_next_decl_tag(const struct btf *btf, const struct btf_type *pt,
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 0f7828380895..64538625ee91 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6392,19 +6392,24 @@ static bool is_void_or_int_ptr(struct btf *btf, const struct btf_type *t)
 }
 
 static u32 get_ctx_arg_idx(struct btf *btf, const struct btf_type *func_proto,
-			   int off)
+			   int off, int *aligned_idx)
 {
 	const struct btf_param *args;
 	const struct btf_type *t;
 	u32 offset = 0, nr_args;
 	int i;
 
+	if (aligned_idx)
+		*aligned_idx = -ENOENT;
+
 	if (!func_proto)
 		return off / 8;
 
 	nr_args = btf_type_vlen(func_proto);
 	args = (const struct btf_param *)(func_proto + 1);
 	for (i = 0; i < nr_args; i++) {
+		if (aligned_idx && offset == off)
+			*aligned_idx = i;
 		t = btf_type_skip_modifiers(btf, args[i].type, NULL);
 		offset += btf_type_is_ptr(t) ? 8 : roundup(t->size, 8);
 		if (off < offset)
@@ -6671,7 +6676,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 			tname, off);
 		return false;
 	}
-	arg = get_ctx_arg_idx(btf, t, off);
+	arg = get_ctx_arg_idx(btf, t, off, NULL);
 	args = (const struct btf_param *)(t + 1);
 	/* if (t == NULL) Fall back to default BPF prog with
 	 * MAX_BPF_FUNC_REG_ARGS u64 arguments.
@@ -6681,6 +6686,9 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 		/* skip first 'void *__data' argument in btf_trace_##name typedef */
 		args++;
 		nr_args--;
+		prog->aux->accessed_args |= (1 << (arg + 1));
+	} else {
+		prog->aux->accessed_args |= (1 << arg);
 	}
 
 	if (arg > nr_args) {
@@ -7540,6 +7548,102 @@ int btf_check_type_match(struct bpf_verifier_log *log, const struct bpf_prog *pr
 	return btf_check_func_type_match(log, btf1, t1, btf2, t2);
 }
 
+static u32 get_ctx_arg_total_size(struct btf *btf, const struct btf_type *t)
+{
+	const struct btf_param *args;
+	u32 size = 0, nr_args;
+	int i;
+
+	nr_args = btf_type_vlen(t);
+	args = (const struct btf_param *)(t + 1);
+	for (i = 0; i < nr_args; i++) {
+		t = btf_type_skip_modifiers(btf, args[i].type, NULL);
+		size += btf_type_is_ptr(t) ? 8 : roundup(t->size, 8);
+	}
+
+	return size;
+}
+
+/* This function is similar to btf_check_func_type_match(), except that it
+ * only compare some function args of the function prototype t1 and t2.
+ */
+int btf_check_func_part_match(struct btf *btf1, const struct btf_type *func1,
+			      struct btf *btf2, const struct btf_type *func2,
+			      u64 func_args)
+{
+	const struct btf_param *args1, *args2;
+	u32 nargs1, i, offset = 0;
+	const char *s1, *s2;
+
+	if (!btf_type_is_func_proto(func1) || !btf_type_is_func_proto(func2))
+		return -EINVAL;
+
+	args1 = (const struct btf_param *)(func1 + 1);
+	args2 = (const struct btf_param *)(func2 + 1);
+	nargs1 = btf_type_vlen(func1);
+
+	for (i = 0; i <= nargs1; i++) {
+		const struct btf_type *t1, *t2;
+
+		if (!(func_args & (1 << i)))
+			goto next;
+
+		if (i < nargs1) {
+			int t2_index;
+
+			/* get the index of the arg corresponding to args1[i]
+			 * by the offset.
+			 */
+			get_ctx_arg_idx(btf2, func2, offset, &t2_index);
+			if (t2_index < 0)
+				return -EINVAL;
+
+			t1 = btf_type_skip_modifiers(btf1, args1[i].type, NULL);
+			t2 = btf_type_skip_modifiers(btf2, args2[t2_index].type,
+						     NULL);
+		} else {
+			/* i == nargs1, this is the index of return value of t1 */
+			if (get_ctx_arg_total_size(btf1, func1) !=
+			    get_ctx_arg_total_size(btf2, func2))
+				return -EINVAL;
+
+			/* check the return type of t1 and t2 */
+			t1 = btf_type_skip_modifiers(btf1, func1->type, NULL);
+			t2 = btf_type_skip_modifiers(btf2, func2->type, NULL);
+		}
+
+		if (t1->info != t2->info ||
+		    (btf_type_has_size(t1) && t1->size != t2->size))
+			return -EINVAL;
+		if (btf_type_is_int(t1) || btf_is_any_enum(t1))
+			goto next;
+
+		if (btf_type_is_struct(t1))
+			goto on_struct;
+
+		if (!btf_type_is_ptr(t1))
+			return -EINVAL;
+
+		t1 = btf_type_skip_modifiers(btf1, t1->type, NULL);
+		t2 = btf_type_skip_modifiers(btf2, t2->type, NULL);
+		if (!btf_type_is_struct(t1) || !btf_type_is_struct(t2))
+			return -EINVAL;
+
+on_struct:
+		s1 = btf_name_by_offset(btf1, t1->name_off);
+		s2 = btf_name_by_offset(btf2, t2->name_off);
+		if (strcmp(s1, s2))
+			return -EINVAL;
+next:
+		if (i < nargs1) {
+			t1 = btf_type_skip_modifiers(btf1, args1[i].type, NULL);
+			offset += btf_type_is_ptr(t1) ? 8 : roundup(t1->size, 8);
+		}
+	}
+
+	return 0;
+}
+
 static bool btf_is_dynptr_ptr(const struct btf *btf, const struct btf_type *t)
 {
 	const char *name;
-- 
2.39.5