netdev - Re: [PATCH v3 bpf-next 01/11] bpf: Move the PTR_TO_BTF_ID check to check_reg

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Date:   Wed, 23 Sep 2020 10:47:51 +0100
From:   Lorenz Bauer <lmb@...udflare.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH v3 bpf-next 01/11] bpf: Move the PTR_TO_BTF_ID check to check_reg_type()

On Tue, 22 Sep 2020 at 19:38, Martin KaFai Lau <kafai@...com> wrote:
>
> On Tue, Sep 22, 2020 at 10:56:55AM +0100, Lorenz Bauer wrote:
> > On Tue, 22 Sep 2020 at 08:04, Martin KaFai Lau <kafai@...com> wrote:
> > >
> > > check_reg_type() checks whether a reg can be used as an arg of a
> > > func_proto.  For PTR_TO_BTF_ID, the check is actually not
> > > completely done until the reg->btf_id is pointing to a
> > > kernel struct that is acceptable by the func_proto.
> > >
> > > Thus, this patch moves the btf_id check into check_reg_type().
> > > The compatible_reg_types[] usage is localized in check_reg_type() now.
> > >
> > > The "if (!btf_id) verbose(...); " is also removed since it won't happen.
> > >
> > > Signed-off-by: Martin KaFai Lau <kafai@...com>
> > > ---
> > >  kernel/bpf/verifier.c | 65 +++++++++++++++++++++++--------------------
> > >  1 file changed, 35 insertions(+), 30 deletions(-)
> > >
> > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > > index 15ab889b0a3f..3ce61c412ea0 100644
> > > --- a/kernel/bpf/verifier.c
> > > +++ b/kernel/bpf/verifier.c
> > > @@ -4028,20 +4028,29 @@ static const struct bpf_reg_types *compatible_reg_types[] = {
> > >         [__BPF_ARG_TYPE_MAX]            = NULL,
> > >  };
> > >
> > > -static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
> > > -                         const struct bpf_reg_types *compatible)
> > > +static int check_reg_type(struct bpf_verifier_env *env, u32 arg,
> > > +                         enum bpf_arg_type arg_type,
> > > +                         const struct bpf_func_proto *fn)
> Yes. I think that works as good.
>
> An idea for the mid term, I think this map helper's arg override logic
> should belong to a new map_ops and this new map_ops can return the whole
> "fn" instead of overriding on an arg-by-arg base.

Yeah, agreed. I've had a similar idea, but no time to implement it yet.

-- 
Lorenz Bauer  |  Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK

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