Commit 1cb80d9e authored by Kui-Feng Lee's avatar Kui-Feng Lee Committed by Alexei Starovoitov
Browse files

bpf: Support __uptr type tag in BTF 



This patch introduces the "__uptr" type tag to BTF. It is to define
a pointer pointing to the user space memory. This patch adds BTF
logic to pass the "__uptr" type tag.

btf_find_kptr() is reused for the "__uptr" tag. The "__uptr" will only
be supported in the map_value of the task storage map. However,
btf_parse_struct_meta() also uses btf_find_kptr() but it is not
interested in "__uptr". This patch adds a "field_mask" argument
to btf_find_kptr() which will return BTF_FIELD_IGNORE if the
caller is not interested in a “__uptr” field.

btf_parse_kptr() is also reused to parse the uptr.
The btf_check_and_fixup_fields() is changed to do extra
checks on the uptr to ensure that its struct size is not larger
than PAGE_SIZE. It is not clear how a uptr pointing to a CO-RE
supported kernel struct will be used, so it is also not allowed now.

Signed-off-by: default avatarKui-Feng Lee <thinker.li@gmail.com>
Signed-off-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20241023234759.860539-2-martin.lau@linux.dev


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 39b8ab15

include/linux/bpf.h

+5 −0
Original line number Diff line number Diff line
@@ -203,6 +203,7 @@ enum btf_field_type { 
	BPF_GRAPH_ROOT = BPF_RB_ROOT | BPF_LIST_HEAD,

	BPF_REFCOUNT   = (1 << 9),

	BPF_WORKQUEUE  = (1 << 10),

	BPF_UPTR       = (1 << 11),

};



typedef void (*btf_dtor_kfunc_t)(void *);
@@ -322,6 +323,8 @@ static inline const char *btf_field_type_name(enum btf_field_type type) 
		return "kptr";

	case BPF_KPTR_PERCPU:

		return "percpu_kptr";

	case BPF_UPTR:

		return "uptr";

	case BPF_LIST_HEAD:

		return "bpf_list_head";

	case BPF_LIST_NODE:
@@ -350,6 +353,7 @@ static inline u32 btf_field_type_size(enum btf_field_type type) 
	case BPF_KPTR_UNREF:

	case BPF_KPTR_REF:

	case BPF_KPTR_PERCPU:

	case BPF_UPTR:

		return sizeof(u64);

	case BPF_LIST_HEAD:

		return sizeof(struct bpf_list_head);
@@ -379,6 +383,7 @@ static inline u32 btf_field_type_align(enum btf_field_type type) 
	case BPF_KPTR_UNREF:

	case BPF_KPTR_REF:

	case BPF_KPTR_PERCPU:

	case BPF_UPTR:

		return __alignof__(u64);

	case BPF_LIST_HEAD:

		return __alignof__(struct bpf_list_head);

kernel/bpf/btf.c

+29 −5
Original line number Diff line number Diff line
@@ -3334,7 +3334,7 @@ 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)

			 u32 off, int sz, struct btf_field_info *info, u32 field_mask)

{

	enum btf_field_type type;

	u32 res_id;
@@ -3358,9 +3358,14 @@ static int btf_find_kptr(const struct btf *btf, const struct btf_type *t, 
		type = BPF_KPTR_REF;

	else if (!strcmp("percpu_kptr", __btf_name_by_offset(btf, t->name_off)))

		type = BPF_KPTR_PERCPU;

	else if (!strcmp("uptr", __btf_name_by_offset(btf, t->name_off)))

		type = BPF_UPTR;

	else

		return -EINVAL;



	if (!(type & field_mask))

		return BTF_FIELD_IGNORE;



	/* Get the base type */

	t = btf_type_skip_modifiers(btf, t->type, &res_id);

	/* Only pointer to struct is allowed */
@@ -3502,7 +3507,7 @@ static int btf_get_field_type(const struct btf *btf, const struct btf_type *var_ 
	field_mask_test_name(BPF_REFCOUNT,  "bpf_refcount");



	/* Only return BPF_KPTR when all other types with matchable names fail */

	if (field_mask & BPF_KPTR && !__btf_type_is_struct(var_type)) {

	if (field_mask & (BPF_KPTR | BPF_UPTR) && !__btf_type_is_struct(var_type)) {

		type = BPF_KPTR_REF;

		goto end;

	}
@@ -3535,6 +3540,7 @@ static int btf_repeat_fields(struct btf_field_info *info, 
		case BPF_KPTR_UNREF:

		case BPF_KPTR_REF:

		case BPF_KPTR_PERCPU:

		case BPF_UPTR:

		case BPF_LIST_HEAD:

		case BPF_RB_ROOT:

			break;
@@ -3661,8 +3667,9 @@ static int btf_find_field_one(const struct btf *btf, 
	case BPF_KPTR_UNREF:

	case BPF_KPTR_REF:

	case BPF_KPTR_PERCPU:

	case BPF_UPTR:

		ret = btf_find_kptr(btf, var_type, off, sz,

				    info_cnt ? &info[0] : &tmp);

				    info_cnt ? &info[0] : &tmp, field_mask);

		if (ret < 0)

			return ret;

		break;
@@ -3985,6 +3992,7 @@ struct btf_record *btf_parse_fields(const struct btf *btf, const struct btf_type 
		case BPF_KPTR_UNREF:

		case BPF_KPTR_REF:

		case BPF_KPTR_PERCPU:

		case BPF_UPTR:

			ret = btf_parse_kptr(btf, &rec->fields[i], &info_arr[i]);

			if (ret < 0)

				goto end;
@@ -4044,12 +4052,28 @@ int btf_check_and_fixup_fields(const struct btf *btf, struct btf_record *rec) 
	 * Hence we only need to ensure that bpf_{list_head,rb_root} ownership

	 * does not form cycles.

	 */

	if (IS_ERR_OR_NULL(rec) || !(rec->field_mask & BPF_GRAPH_ROOT))

	if (IS_ERR_OR_NULL(rec) || !(rec->field_mask & (BPF_GRAPH_ROOT | BPF_UPTR)))

		return 0;

	for (i = 0; i < rec->cnt; i++) {

		struct btf_struct_meta *meta;

		const struct btf_type *t;

		u32 btf_id;



		if (rec->fields[i].type == BPF_UPTR) {

			/* The uptr only supports pinning one page and cannot

			 * point to a kernel struct

			 */

			if (btf_is_kernel(rec->fields[i].kptr.btf))

				return -EINVAL;

			t = btf_type_by_id(rec->fields[i].kptr.btf,

					   rec->fields[i].kptr.btf_id);

			if (!t->size)

				return -EINVAL;

			if (t->size > PAGE_SIZE)

				return -E2BIG;

			continue;

		}



		if (!(rec->fields[i].type & BPF_GRAPH_ROOT))

			continue;

		btf_id = rec->fields[i].graph_root.value_btf_id;
@@ -5560,7 +5584,7 @@ btf_parse_struct_metas(struct bpf_verifier_log *log, struct btf *btf) 
			goto free_aof;

		}



		ret = btf_find_kptr(btf, t, 0, 0, &tmp);

		ret = btf_find_kptr(btf, t, 0, 0, &tmp, BPF_KPTR);

		if (ret != BTF_FIELD_FOUND)

			continue;

kernel/bpf/syscall.c

+2 −0
Original line number Diff line number Diff line
@@ -548,6 +548,7 @@ void btf_record_free(struct btf_record *rec) 
		case BPF_KPTR_UNREF:

		case BPF_KPTR_REF:

		case BPF_KPTR_PERCPU:

		case BPF_UPTR:

			if (rec->fields[i].kptr.module)

				module_put(rec->fields[i].kptr.module);

			if (btf_is_kernel(rec->fields[i].kptr.btf))
@@ -597,6 +598,7 @@ struct btf_record *btf_record_dup(const struct btf_record *rec) 
		case BPF_KPTR_UNREF:

		case BPF_KPTR_REF:

		case BPF_KPTR_PERCPU:

		case BPF_UPTR:

			if (btf_is_kernel(fields[i].kptr.btf))

				btf_get(fields[i].kptr.btf);

			if (fields[i].kptr.module && !try_module_get(fields[i].kptr.module)) {