Re: [RFC bpf-next v3 06/11] bpf: validate value_type

[Kui-Feng Lee <sinquersw@xxxxxxxxx>]

On 9/25/23 18:03, Martin KaFai Lau wrote:
> On 9/20/23 8:59 AM, thinker.li@xxxxxxxxx wrote:
> > From: Kui-Feng Lee <thinker.li@xxxxxxxxx>
> >
> > A value_type should has three members; refcnt, state, and data.
> >
> > Signed-off-by: Kui-Feng Lee <thinker.li@xxxxxxxxx>
> > ---
> >   kernel/bpf/bpf_struct_ops.c | 75 +++++++++++++++++++++++++++++++++++++
> >   1 file changed, 75 insertions(+)
> >
> > diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> > index ef8a1edec891..fb684d2ee99d 100644
> > --- a/kernel/bpf/bpf_struct_ops.c
> > +++ b/kernel/bpf/bpf_struct_ops.c
> > @@ -99,6 +99,79 @@ const struct bpf_prog_ops bpf_struct_ops_prog_ops = {
> >   static const struct btf_type *module_type;
> > +static bool check_value_member(struct btf *btf,
> > +                   const struct btf_member *member,
> > +                   int index,
> > +                   const char *value_name,
> > +                   const char *name, const char *type_name,
> > +                   u16 kind)
> > +{
> > +    const char *mname, *mtname;
> > +    const struct btf_type *mt;
> > +    s32 mtype_id;
> > +
> > +    mname = btf_name_by_offset(btf, member->name_off);
> > +    if (!*mname) {
> > +        pr_warn("The member %d of %s should have a name\n",
> > +            index, value_name);
> > +        return false;
> > +    }
> > +    if (strcmp(mname, name)) {
> > +        pr_warn("The member %d of %s should be refcnt\n",
> > +            index, value_name);
> > +        return false;
> > +    }
> > +    mtype_id = member->type;
> > +    mt = btf_type_by_id(btf, mtype_id);
> > +    mtname = btf_name_by_offset(btf, mt->name_off);
> > +    if (!*mtname) {
> > +        pr_warn("The type of the member %d of %s should have a name\n",
> > +            index, value_name);
> > +        return false;
> > +    }
> > +    if (strcmp(mtname, type_name)) {
> > +        pr_warn("The type of the member %d of %s should be 
> > refcount_t\n",
> > +            index, value_name);
> > +        return false;
> > +    }
> > +    if (btf_kind(mt) != kind) {
> > +        pr_warn("The type of the member %d of %s should be %d\n",
> > +            index, value_name, btf_kind(mt));
> > +        return false;
> > +    }
> > +
> > +    return true;
> > +}
> > +
> > +static bool is_valid_value_type(struct btf *btf, s32 value_id,
> > +                const char *type_name, const char *value_name)
> > +{
> > +    const struct btf_member *member;
> > +    const struct btf_type *vt;
> > +
> > +    vt = btf_type_by_id(btf, value_id);
> > +    if (btf_vlen(vt) != 3) {
> > +        pr_warn("The number of %s's members should be 3, but we get 
> > %d\n",
> > +            value_name, btf_vlen(vt));
> > +        return false;
> > +    }
> > +    member = btf_type_member(vt);
> > +    if (!check_value_member(btf, member, 0, value_name,
> > +                "refcnt", "refcount_t", BTF_KIND_TYPEDEF))
> > +        return false;
> > +    member++;
> > +    if (!check_value_member(btf, member, 1, value_name,
> > +                "state", "bpf_struct_ops_state",
> > +                BTF_KIND_ENUM))
> > +        return false;
> > +    member++;
>
> I wonder if giving BPF_STRUCT_OPS_COMMON_VALUE a proper struct will make 
> the validation cleaner. Like,
>
> struct bpf_struct_ops_common {
>      refcount_t refcnt;
>      enum bpf_struct_ops_state state;
> };
>
> wdyt?

It should work.

> > +    if (!check_value_member(btf, member, 2, value_name,
> > +                "data", type_name, BTF_KIND_STRUCT))
>
> Instead of checking name, I think this can directly check with the 
> st_ops->type.

Make sense

> > +        return false;
> > +
> > +    return true;
> > +}