Commit 1c6d28a6 authored by Jiri Olsa's avatar Jiri Olsa Committed by Alexei Starovoitov
Browse files

bpf: Factor btf_struct_access function 



Adding btf_struct_walk function that walks through the
struct type + given offset and returns following values:

  enum bpf_struct_walk_result {
       /* < 0 error */
       WALK_SCALAR = 0,
       WALK_PTR,
       WALK_STRUCT,
  };

WALK_SCALAR - when SCALAR_VALUE is found
WALK_PTR    - when pointer value is found, its ID is stored
              in 'next_btf_id' output param
WALK_STRUCT - when nested struct object is found, its ID is stored
              in 'next_btf_id' output param

It will be used in following patches to get all nested
struct objects for given type and offset.

The btf_struct_access now calls btf_struct_walk function,
as long as it gets nested structs as return value.

Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200825192124.710397-8-jolsa@kernel.org
parent dafe58fc

kernel/bpf/btf.c

+65 −10
Original line number Diff line number Diff line
@@ -3886,16 +3886,22 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, 
	return true;

}



int btf_struct_access(struct bpf_verifier_log *log,

enum bpf_struct_walk_result {

	/* < 0 error */

	WALK_SCALAR = 0,

	WALK_PTR,

	WALK_STRUCT,

};



static int btf_struct_walk(struct bpf_verifier_log *log,

			   const struct btf_type *t, int off, int size,

		      enum bpf_access_type atype,

			   u32 *next_btf_id)

{

	u32 i, moff, mtrue_end, msize = 0, total_nelems = 0;

	const struct btf_type *mtype, *elem_type = NULL;

	const struct btf_member *member;

	const char *tname, *mname;

	u32 vlen;

	u32 vlen, elem_id, mid;



again:

	tname = __btf_name_by_offset(btf_vmlinux, t->name_off);
@@ -3966,7 +3972,7 @@ int btf_struct_access(struct bpf_verifier_log *log, 
			 */

			if (off <= moff &&

			    BITS_ROUNDUP_BYTES(end_bit) <= off + size)

				return SCALAR_VALUE;

				return WALK_SCALAR;



			/* off may be accessing a following member

			 *
@@ -3988,11 +3994,13 @@ int btf_struct_access(struct bpf_verifier_log *log, 
			break;



		/* type of the field */

		mid = member->type;

		mtype = btf_type_by_id(btf_vmlinux, member->type);

		mname = __btf_name_by_offset(btf_vmlinux, member->name_off);



		mtype = __btf_resolve_size(btf_vmlinux, mtype, &msize,

					   &elem_type, NULL, &total_nelems, NULL);

					   &elem_type, &elem_id, &total_nelems,

					   &mid);

		if (IS_ERR(mtype)) {

			bpf_log(log, "field %s doesn't have size\n", mname);

			return -EFAULT;
@@ -4054,6 +4062,7 @@ int btf_struct_access(struct bpf_verifier_log *log, 
			elem_idx = (off - moff) / msize;

			moff += elem_idx * msize;

			mtype = elem_type;

			mid = elem_id;

		}



		/* the 'off' we're looking for is either equal to start
@@ -4063,6 +4072,12 @@ int btf_struct_access(struct bpf_verifier_log *log, 
			/* our field must be inside that union or struct */

			t = mtype;



			/* return if the offset matches the member offset */

			if (off == moff) {

				*next_btf_id = mid;

				return WALK_STRUCT;

			}



			/* adjust offset we're looking for */

			off -= moff;

			goto again;
@@ -4078,11 +4093,10 @@ int btf_struct_access(struct bpf_verifier_log *log, 
					mname, moff, tname, off, size);

				return -EACCES;

			}



			stype = btf_type_skip_modifiers(btf_vmlinux, mtype->type, &id);

			if (btf_type_is_struct(stype)) {

				*next_btf_id = id;

				return PTR_TO_BTF_ID;

				return WALK_PTR;

			}

		}
@@ -4099,12 +4113,53 @@ int btf_struct_access(struct bpf_verifier_log *log, 
			return -EACCES;

		}



		return SCALAR_VALUE;

		return WALK_SCALAR;

	}

	bpf_log(log, "struct %s doesn't have field at offset %d\n", tname, off);

	return -EINVAL;

}



int btf_struct_access(struct bpf_verifier_log *log,

		      const struct btf_type *t, int off, int size,

		      enum bpf_access_type atype __maybe_unused,

		      u32 *next_btf_id)

{

	int err;

	u32 id;



	do {

		err = btf_struct_walk(log, t, off, size, &id);



		switch (err) {

		case WALK_PTR:

			/* If we found the pointer or scalar on t+off,

			 * we're done.

			 */

			*next_btf_id = id;

			return PTR_TO_BTF_ID;

		case WALK_SCALAR:

			return SCALAR_VALUE;

		case WALK_STRUCT:

			/* We found nested struct, so continue the search

			 * by diving in it. At this point the offset is

			 * aligned with the new type, so set it to 0.

			 */

			t = btf_type_by_id(btf_vmlinux, id);

			off = 0;

			break;

		default:

			/* It's either error or unknown return value..

			 * scream and leave.

			 */

			if (WARN_ONCE(err > 0, "unknown btf_struct_walk return value"))

				return -EINVAL;

			return err;

		}

	} while (t);



	return -EINVAL;

}



int btf_resolve_helper_id(struct bpf_verifier_log *log,

			  const struct bpf_func_proto *fn, int arg)

{