Re: [PATCH bpf v2 1/5] bpf: Adapt 32-bit return value kfunc for 32-bit ARM when zext extension

[Yang Jihong]

Hello,

On 2022/11/9 7:12, Martin KaFai Lau wrote:
> On 11/7/22 1:20 AM, Yang Jihong wrote:
> > For ARM32 architecture, if data width of kfunc return value is 32 bits,
> > need to do explicit zero extension for high 32-bit, insn_def_regno should
> > return dst_reg for BPF_JMP type of BPF_PSEUDO_KFUNC_CALL. Otherwise,
> > opt_subreg_zext_lo32_rnd_hi32 returns -EFAULT, resulting in BPF failure.
> >
> > Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
> > ---
> >   kernel/bpf/verifier.c | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 7f0a9f6cb889..bac37757ffca 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -2404,6 +2404,9 @@ static int insn_def_regno(const struct bpf_insn 
> > *insn)
> >   {
> >       switch (BPF_CLASS(insn->code)) {
> >       case BPF_JMP:
> > +        if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL)
> > +            return insn->dst_reg;
>
> This does not look right.  A kfunc can return void.  The btf type of the 
> kfunc's return value needs to be checked against "void" first?
OK, will add the check in next version.

> Also, this will affect insn_has_def32(), does is_reg64 (called from 
> insn_has_def32) need to be adjusted also?
Yes, is_reg64 need to be adjusted, will fix in next version.
> For patch 2, as replied earlier in v1, I would separate out the prog 
> that does __sk_buff->sk and use the uapi's bpf.h instead of vmlinux.h 
> since it does not need CO-RE.
OK, will remove adjust sk check patches in next verion.

As mentioned in v1:
"bpf-tc program can take'struct sk_buff *skb' instead of'struct
__sk_buff *skb' but it will be a separate topic."

It is a separate topic, only the lskel test cases are affected.
The ARM32 kfunc function is not affected.

> This set should target for bpf-next instead of bpf.
OK, will send to bpf-next in next version.

Thanks,
Yang