On Tue, Jun 30, 2020 at 1:05 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Thu, Jun 25, 2020 at 4:49 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > Adding btf_struct_address function that takes 2 BTF objects
> > and offset as arguments and checks whether object A is nested
> > in object B on given offset.
> >
> > This function will be used when checking the helper function
> > PTR_TO_BTF_ID arguments. If the argument has an offset value,
> > the btf_struct_address will check if the final address is
> > the expected BTF ID.
> >
> > This way we can access nested BTF objects under PTR_TO_BTF_ID
> > pointer type and pass them to helpers, while they still point
> > to valid kernel BTF objects.
> >
> > Using btf_struct_access to implement new btf_struct_address
> > function, because it already walks down the given BTF object.
> >
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> > include/linux/bpf.h | 3 ++
> > kernel/bpf/btf.c | 67 ++++++++++++++++++++++++++++++++++++++-----
> > kernel/bpf/verifier.c | 37 +++++++++++++++---------
> > 3 files changed, 87 insertions(+), 20 deletions(-)
> >
[...]
> >
> > error:
> > bpf_log(log, "access beyond struct %s at off %u size %u\n",
> > @@ -4043,9 +4054,21 @@ int btf_struct_access(struct bpf_verifier_log *log,
> >
> > /* adjust offset we're looking for */
> > off -= moff;
> > +
> > + /* We are nexting into another struct,
> > + * check if we are crossing expected ID.
> > + */
> > + if (data->op == ACCESS_EXPECT && !off && t == data->exp_type)
>
> before you can do this type check, you need to btf_type_skip_modifiers() first.
>
Ignore this part, btf_resolve_size() (somewhat unexpectedly) already does that.
> > + return 0;
> > goto again;
> > }
> >
> > + /* We are interested only in structs for expected ID,
> > + * bail out.
> > + */
> > + if (data->op == ACCESS_EXPECT)
> > + return -EINVAL;
> > +
> > if (btf_type_is_ptr(mtype)) {
> > const struct btf_type *stype;
> > u32 id;
[...]
