[PATCH bpf-next v2 02/15] bpf: Make btf_find_field more generic

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

Next commit's field type will not be struct, but pointer, and it will
not be limited to one offset, but multiple ones. Make existing
btf_find_struct_field and btf_find_datasec_var functions amenable to use
for finding BTF ID pointers in map value, by taking a moving spin_lock
and timer specific checks into their own function.

The alignment, and name are checked before the function is called, so it
is the last point where we can skip field or return an error before the
next loop iteration happens. This is important, because we'll be
potentially reallocating memory inside this function in next commit, so
being able to do that when everything else is in order is going to be
more convenient.

The name parameter is now optional, and only checked if it is not NULL.

The size must be checked in the function, because in case of PTR it will
instead point to the underlying BTF ID it is pointing to (or modifiers),
so the check becomes wrong to do outside of function, and the base type
has to be obtained by removing modifiers.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/btf.c | 120 +++++++++++++++++++++++++++++++++--------------
 1 file changed, 86 insertions(+), 34 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 17b9adcd88d3..5b2824332880 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3161,71 +3161,109 @@ static void btf_struct_log(struct btf_verifier_env *env,
 	btf_verifier_log(env, "size=%u vlen=%u", t->size, btf_type_vlen(t));
 }
 
+enum {
+	BTF_FIELD_SPIN_LOCK,
+	BTF_FIELD_TIMER,
+};
+
+struct btf_field_info {
+	u32 off;
+};
+
+static int btf_find_field_struct(const struct btf *btf, const struct btf_type *t,
+				 u32 off, int sz, struct btf_field_info *info)
+{
+	if (!__btf_type_is_struct(t))
+		return 0;
+	if (t->size != sz)
+		return 0;
+	if (info->off != -ENOENT)
+		/* only one such field is allowed */
+		return -E2BIG;
+	info->off = off;
+	return 0;
+}
+
 static int btf_find_struct_field(const struct btf *btf, const struct btf_type *t,
-				 const char *name, int sz, int align)
+				 const char *name, int sz, int align, int field_type,
+				 struct btf_field_info *info)
 {
 	const struct btf_member *member;
-	u32 i, off = -ENOENT;
+	u32 i, off;
+	int ret;
 
 	for_each_member(i, t, member) {
 		const struct btf_type *member_type = btf_type_by_id(btf,
 								    member->type);
-		if (!__btf_type_is_struct(member_type))
-			continue;
-		if (member_type->size != sz)
-			continue;
-		if (strcmp(__btf_name_by_offset(btf, member_type->name_off), name))
-			continue;
-		if (off != -ENOENT)
-			/* only one such field is allowed */
-			return -E2BIG;
+
 		off = __btf_member_bit_offset(t, member);
+
+		if (name && strcmp(__btf_name_by_offset(btf, member_type->name_off), name))
+			continue;
 		if (off % 8)
 			/* valid C code cannot generate such BTF */
 			return -EINVAL;
 		off /= 8;
 		if (off % align)
 			return -EINVAL;
+
+		switch (field_type) {
+		case BTF_FIELD_SPIN_LOCK:
+		case BTF_FIELD_TIMER:
+			ret = btf_find_field_struct(btf, member_type, off, sz, info);
+			if (ret < 0)
+				return ret;
+			break;
+		default:
+			return -EFAULT;
+		}
 	}
-	return off;
+	return 0;
 }
 
 static int btf_find_datasec_var(const struct btf *btf, const struct btf_type *t,
-				const char *name, int sz, int align)
+				const char *name, int sz, int align, int field_type,
+				struct btf_field_info *info)
 {
 	const struct btf_var_secinfo *vsi;
-	u32 i, off = -ENOENT;
+	u32 i, off;
+	int ret;
 
 	for_each_vsi(i, t, vsi) {
 		const struct btf_type *var = btf_type_by_id(btf, vsi->type);
 		const struct btf_type *var_type = btf_type_by_id(btf, var->type);
 
-		if (!__btf_type_is_struct(var_type))
-			continue;
-		if (var_type->size != sz)
+		off = vsi->offset;
+
+		if (name && strcmp(__btf_name_by_offset(btf, var_type->name_off), name))
 			continue;
 		if (vsi->size != sz)
 			continue;
-		if (strcmp(__btf_name_by_offset(btf, var_type->name_off), name))
-			continue;
-		if (off != -ENOENT)
-			/* only one such field is allowed */
-			return -E2BIG;
-		off = vsi->offset;
 		if (off % align)
 			return -EINVAL;
+
+		switch (field_type) {
+		case BTF_FIELD_SPIN_LOCK:
+		case BTF_FIELD_TIMER:
+			ret = btf_find_field_struct(btf, var_type, off, sz, info);
+			if (ret < 0)
+				return ret;
+			break;
+		default:
+			return -EFAULT;
+		}
 	}
-	return off;
+	return 0;
 }
 
 static int btf_find_field(const struct btf *btf, const struct btf_type *t,
-			  const char *name, int sz, int align)
+			  const char *name, int sz, int align, int field_type,
+			  struct btf_field_info *info)
 {
-
 	if (__btf_type_is_struct(t))
-		return btf_find_struct_field(btf, t, name, sz, align);
+		return btf_find_struct_field(btf, t, name, sz, align, field_type, info);
 	else if (btf_type_is_datasec(t))
-		return btf_find_datasec_var(btf, t, name, sz, align);
+		return btf_find_datasec_var(btf, t, name, sz, align, field_type, info);
 	return -EINVAL;
 }
 
@@ -3235,16 +3273,30 @@ static int btf_find_field(const struct btf *btf, const struct btf_type *t,
  */
 int btf_find_spin_lock(const struct btf *btf, const struct btf_type *t)
 {
-	return btf_find_field(btf, t, "bpf_spin_lock",
-			      sizeof(struct bpf_spin_lock),
-			      __alignof__(struct bpf_spin_lock));
+	struct btf_field_info info = { .off = -ENOENT };
+	int ret;
+
+	ret = btf_find_field(btf, t, "bpf_spin_lock",
+			     sizeof(struct bpf_spin_lock),
+			     __alignof__(struct bpf_spin_lock),
+			     BTF_FIELD_SPIN_LOCK, &info);
+	if (ret < 0)
+		return ret;
+	return info.off;
 }
 
 int btf_find_timer(const struct btf *btf, const struct btf_type *t)
 {
-	return btf_find_field(btf, t, "bpf_timer",
-			      sizeof(struct bpf_timer),
-			      __alignof__(struct bpf_timer));
+	struct btf_field_info info = { .off = -ENOENT };
+	int ret;
+
+	ret = btf_find_field(btf, t, "bpf_timer",
+			     sizeof(struct bpf_timer),
+			     __alignof__(struct bpf_timer),
+			     BTF_FIELD_TIMER, &info);
+	if (ret < 0)
+		return ret;
+	return info.off;
 }
 
 static void __btf_struct_show(const struct btf *btf, const struct btf_type *t,
-- 
2.35.1