On Mon, Sep 13, 2021 at 8:51 AM Yonghong Song <yhs@xxxxxx> wrote:
>
> LLVM14 added support for a new C attribute ([1])
> __attribute__((btf_tag("arbitrary_str")))
> This attribute will be emitted to dwarf ([2]) and pahole
> will convert it to BTF. Or for bpf target, this
> attribute will be emitted to BTF directly ([3], [4]).
> The attribute is intended to provide additional
> information for
> - struct/union type or struct/union member
> - static/global variables
> - static/global function or function parameter.
>
> For linux kernel, the btf_tag can be applied
> in various places to specify user pointer,
> function pre- or post- condition, function
> allow/deny in certain context, etc. Such information
> will be encoded in vmlinux BTF and can be used
> by verifier.
>
> The btf_tag can also be applied to bpf programs
> to help global verifiable functions, e.g.,
> specifying preconditions, etc.
>
> This patch added basic parsing and checking support
> in kernel for new BTF_KIND_TAG kind.
>
> [1] https://reviews.llvm.org/D106614
> [2] https://reviews.llvm.org/D106621
> [3] https://reviews.llvm.org/D106622
> [4] https://reviews.llvm.org/D109560
>
> Signed-off-by: Yonghong Song <yhs@xxxxxx>
> ---
> include/uapi/linux/btf.h | 16 ++++-
> kernel/bpf/btf.c | 120 +++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/btf.h | 16 ++++-
> 3 files changed, 148 insertions(+), 4 deletions(-)
>
[...]
>
> +static s32 btf_tag_check_meta(struct btf_verifier_env *env,
> + const struct btf_type *t,
> + u32 meta_left)
> +{
> + const struct btf_tag *tag;
> + u32 meta_needed = sizeof(*tag);
> + const char *value;
> +
> + if (meta_left < meta_needed) {
> + btf_verifier_log_basic(env, t,
> + "meta_left:%u meta_needed:%u",
> + meta_left, meta_needed);
> + return -EINVAL;
> + }
> +
> + value = btf_name_by_offset(env->btf, t->name_off);
> + if (!value || !value[0]) {
> + btf_verifier_log_type(env, t, "Invalid value");
> + return -EINVAL;
> + }
> +
> + if (btf_type_vlen(t)) {
> + btf_verifier_log_type(env, t, "vlen != 0");
> + return -EINVAL;
> + }
> +
> + if (btf_type_kflag(t)) {
> + btf_verifier_log_type(env, t, "Invalid btf_info kind_flag");
> + return -EINVAL;
> + }
> +
probably need to enforce that component_idx is >= -1? -2 is not a
valid supported value right now.
> + btf_verifier_log_type(env, t, NULL);
> +
> + return meta_needed;
> +}
> +
> +static int btf_tag_resolve(struct btf_verifier_env *env,
> + const struct resolve_vertex *v)
> +{
> + const struct btf_type *next_type;
> + const struct btf_type *t = v->t;
> + u32 next_type_id = t->type;
> + struct btf *btf = env->btf;
> + s32 component_idx;
> + u32 vlen;
> +
> + next_type = btf_type_by_id(btf, next_type_id);
> + if (!next_type || !btf_type_is_tag_target(next_type)) {
> + btf_verifier_log_type(env, v->t, "Invalid type_id");
> + return -EINVAL;
> + }
> +
> + if (!env_type_is_resolve_sink(env, next_type) &&
> + !env_type_is_resolved(env, next_type_id))
> + return env_stack_push(env, next_type, next_type_id);
> +
> + component_idx = btf_type_tag(t)->component_idx;
> + if (component_idx != -1) {
so here, if it's -2, that should be an error, but currently will be
ignored, right?
> + if (btf_type_is_var(next_type) || component_idx < 0) {
if is_var(next_type) then component_idx should only be -1, nothing
else. Or am I missing some convention?
> + btf_verifier_log_type(env, v->t, "Invalid component_idx");
> + return -EINVAL;
> + }
> +
> + if (btf_type_is_struct(next_type)) {
> + vlen = btf_type_vlen(next_type);
> + } else {
> + next_type = btf_type_by_id(btf, next_type->type);
> + vlen = btf_type_vlen(next_type);
> + }
> +
> + if ((u32)component_idx >= vlen) {
> + btf_verifier_log_type(env, v->t, "Invalid component_idx");
> + return -EINVAL;
> + }
> + }
> +
> + env_stack_pop_resolved(env, next_type_id, 0);
> +
> + return 0;
> +}
> +
[...]
