bpf: Refactor kptr_off_tab into btf_record

To prepare the BPF verifier to handle special fields in both map values
and program allocated types coming from program BTF, we need to refactor
the kptr_off_tab handling code into something more generic and reusable
across both cases to avoid code duplication.

Later patches also require passing this data to helpers at runtime, so
that they can work on user defined types, initialize them, destruct
them, etc.

The main observation is that both map values and such allocated types
point to a type in program BTF, hence they can be handled similarly. We
can prepare a field metadata table for both cases and store them in
struct bpf_map or struct btf depending on the use case.

Hence, refactor the code into generic btf_record and btf_field member
structs. The btf_record represents the fields of a specific btf_type in
user BTF. The cnt indicates the number of special fields we successfully
recognized, and field_mask is a bitmask of fields that were found, to
enable quick determination of availability of a certain field.

Subsequently, refactor the rest of the code to work with these generic
types, remove assumptions about kptr and kptr_off_tab, rename variables
to more meaningful names, etc.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20221103191013.1236066-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 31 insertions, 36 deletions

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index f4d21eef6ebd..8391a77138ee 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3191,7 +3191,7 @@ 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_type {
+enum btf_field_info_type {
 	BTF_FIELD_SPIN_LOCK,
 	BTF_FIELD_TIMER,
 	BTF_FIELD_KPTR,
@@ -3203,9 +3203,9 @@ enum {
 };
 
 struct btf_field_info {
-	u32 type_id;
+	enum btf_field_type type;
 	u32 off;
-	enum bpf_kptr_type type;
+	u32 type_id;
 };
 
 static int btf_find_struct(const struct btf *btf, const struct btf_type *t,
@@ -3222,7 +3222,7 @@ static int btf_find_struct(const struct btf *btf, const struct btf_type *t,
 static int btf_find_kptr(const struct btf *btf, const struct btf_type *t,
 			 u32 off, int sz, struct btf_field_info *info)
 {
-	enum bpf_kptr_type type;
+	enum btf_field_type type;
 	u32 res_id;
 
 	/* Permit modifiers on the pointer itself */
@@ -3259,7 +3259,7 @@ static int btf_find_kptr(const struct btf *btf, const struct btf_type *t,
 
 static int btf_find_struct_field(const struct btf *btf, const struct btf_type *t,
 				 const char *name, int sz, int align,
-				 enum btf_field_type field_type,
+				 enum btf_field_info_type field_type,
 				 struct btf_field_info *info, int info_cnt)
 {
 	const struct btf_member *member;
@@ -3311,7 +3311,7 @@ static int btf_find_struct_field(const struct btf *btf, const struct btf_type *t
 
 static int btf_find_datasec_var(const struct btf *btf, const struct btf_type *t,
 				const char *name, int sz, int align,
-				enum btf_field_type field_type,
+				enum btf_field_info_type field_type,
 				struct btf_field_info *info, int info_cnt)
 {
 	const struct btf_var_secinfo *vsi;
@@ -3360,7 +3360,7 @@ static int btf_find_datasec_var(const struct btf *btf, const struct btf_type *t,
 }
 
 static int btf_find_field(const struct btf *btf, const struct btf_type *t,
-			  enum btf_field_type field_type,
+			  enum btf_field_info_type field_type,
 			  struct btf_field_info *info, int info_cnt)
 {
 	const char *name;
@@ -3423,14 +3423,13 @@ int btf_find_timer(const struct btf *btf, const struct btf_type *t)
 	return info.off;
 }
 
-struct bpf_map_value_off *btf_parse_kptrs(const struct btf *btf,
-					  const struct btf_type *t)
+struct btf_record *btf_parse_fields(const struct btf *btf, const struct btf_type *t)
 {
-	struct btf_field_info info_arr[BPF_MAP_VALUE_OFF_MAX];
-	struct bpf_map_value_off *tab;
+	struct btf_field_info info_arr[BTF_FIELDS_MAX];
 	struct btf *kernel_btf = NULL;
 	struct module *mod = NULL;
-	int ret, i, nr_off;
+	struct btf_record *rec;
+	int ret, i, cnt;
 
 	ret = btf_find_field(btf, t, BTF_FIELD_KPTR, info_arr, ARRAY_SIZE(info_arr));
 	if (ret < 0)
@@ -3438,12 +3437,12 @@ struct bpf_map_value_off *btf_parse_kptrs(const struct btf *btf,
 	if (!ret)
 		return NULL;
 
-	nr_off = ret;
-	tab = kzalloc(offsetof(struct bpf_map_value_off, off[nr_off]), GFP_KERNEL | __GFP_NOWARN);
-	if (!tab)
+	cnt = ret;
+	rec = kzalloc(offsetof(struct btf_record, fields[cnt]), GFP_KERNEL | __GFP_NOWARN);
+	if (!rec)
 		return ERR_PTR(-ENOMEM);
-
-	for (i = 0; i < nr_off; i++) {
+	rec->cnt = 0;
+	for (i = 0; i < cnt; i++) {
 		const struct btf_type *t;
 		s32 id;
 
@@ -3500,28 +3499,24 @@ struct bpf_map_value_off *btf_parse_kptrs(const struct btf *btf,
 				ret = -EINVAL;
 				goto end_mod;
 			}
-			tab->off[i].kptr.dtor = (void *)addr;
+			rec->fields[i].kptr.dtor = (void *)addr;
 		}
 
-		tab->off[i].offset = info_arr[i].off;
-		tab->off[i].type = info_arr[i].type;
-		tab->off[i].kptr.btf_id = id;
-		tab->off[i].kptr.btf = kernel_btf;
-		tab->off[i].kptr.module = mod;
+		rec->field_mask |= info_arr[i].type;
+		rec->fields[i].offset = info_arr[i].off;
+		rec->fields[i].type = info_arr[i].type;
+		rec->fields[i].kptr.btf_id = id;
+		rec->fields[i].kptr.btf = kernel_btf;
+		rec->fields[i].kptr.module = mod;
+		rec->cnt++;
 	}
-	tab->nr_off = nr_off;
-	return tab;
+	return rec;
 end_mod:
 	module_put(mod);
 end_btf:
 	btf_put(kernel_btf);
 end:
-	while (i--) {
-		btf_put(tab->off[i].kptr.btf);
-		if (tab->off[i].kptr.module)
-			module_put(tab->off[i].kptr.module);
-	}
-	kfree(tab);
+	btf_record_free(rec);
 	return ERR_PTR(ret);
 }
 
@@ -6370,7 +6365,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 
 		/* kptr_get is only true for kfunc */
 		if (i == 0 && kptr_get) {
-			struct bpf_map_value_off_desc *off_desc;
+			struct btf_field *kptr_field;
 
 			if (reg->type != PTR_TO_MAP_VALUE) {
 				bpf_log(log, "arg#0 expected pointer to map value\n");
@@ -6386,8 +6381,8 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 				return -EINVAL;
 			}
 
-			off_desc = bpf_map_kptr_off_contains(reg->map_ptr, reg->off + reg->var_off.value);
-			if (!off_desc || off_desc->type != BPF_KPTR_REF) {
+			kptr_field = btf_record_find(reg->map_ptr->record, reg->off + reg->var_off.value, BPF_KPTR);
+			if (!kptr_field || kptr_field->type != BPF_KPTR_REF) {
 				bpf_log(log, "arg#0 no referenced kptr at map value offset=%llu\n",
 					reg->off + reg->var_off.value);
 				return -EINVAL;
@@ -6406,8 +6401,8 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
 					func_name, i, btf_type_str(ref_t), ref_tname);
 				return -EINVAL;
 			}
-			if (!btf_struct_ids_match(log, btf, ref_id, 0, off_desc->kptr.btf,
-						  off_desc->kptr.btf_id, true)) {
+			if (!btf_struct_ids_match(log, btf, ref_id, 0, kptr_field->kptr.btf,
+						  kptr_field->kptr.btf_id, true)) {
 				bpf_log(log, "kernel function %s args#%d expected pointer to %s %s\n",
 					func_name, i, btf_type_str(ref_t), ref_tname);
 				return -EINVAL;