On 9/13/21 10:08 PM, Andrii Nakryiko wrote:
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.
I tested below. But I can test here for kernel practice, testing error
case earlier.
+ 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?
It is not. See below. At this point, component_idx could be -2 or 0 or 1 ...
+ 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?
So if it is a variable, the error will return.
If it is not a variable and component_idx < 0 (-2 in this case), return
error. So we do test -2 here.
I will restructure the code to test < -1 earlier, so we won't have
confusion here.
+ 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;
+}
+
[...]
