From 1c6d28a6ac56de5b0af9239a1b02aea4c3011ea3 Mon Sep 17 00:00:00 2001 From: Jiri Olsa Date: Tue, 25 Aug 2020 21:21:17 +0200 Subject: [PATCH] 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: Jiri Olsa Signed-off-by: Alexei Starovoitov Acked-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20200825192124.710397-8-jolsa@kernel.org --- kernel/bpf/btf.c | 75 +++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 65 insertions(+), 10 deletions(-) diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 4488c5b03941..d8d64201c4e0 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -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, - const struct btf_type *t, int off, int size, - enum bpf_access_type atype, - u32 *next_btf_id) +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, + 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 @@ error: */ 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 @@ error: 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 @@ error: 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 @@ error: /* 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 @@ error: 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 @@ error: 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) { -- 2.25.1