linux-kernel - Re: [PATCH bpf] xdp: use trusted arguments in XDP hints kfuncs

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Message-ID: <CAKH8qBtBHD=1bXQyPUczLRUSNagNTKC6DNhO1rqHmrGE5kLHWQ@mail.gmail.com>
Date:   Tue, 11 Jul 2023 10:00:42 -0700
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:     Larysa Zaremba <larysa.zaremba@...el.com>, bpf@...r.kernel.org,
        brouer@...hat.com, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Martin KaFai Lau <martin.lau@...nel.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf] xdp: use trusted arguments in XDP hints kfuncs

On Tue, Jul 11, 2023 at 7:21 AM Jesper Dangaard Brouer
<jbrouer@...hat.com> wrote:
>
>
> On 11/07/2023 12.59, Larysa Zaremba wrote:
> > Currently, verifier does not reject XDP programs that pass NULL pointer to
> > hints functions. At the same time, this case is not handled in any driver
> > implementation (including veth). For example, changing
> >
> > bpf_xdp_metadata_rx_timestamp(ctx, &timestamp);
> >
> > to
> >
> > bpf_xdp_metadata_rx_timestamp(ctx, NULL);
> >
> > in xdp_metadata test successfully crashes the system.
> >
> > Add KF_TRUSTED_ARGS flag to hints kfunc definitions, so driver code
> > does not have to worry about getting invalid pointers.
> >
>
> Looks good to me, assuming this means verifier will reject BPF-prog's
> supplying NULL.
>
> Acked-by: Jesper Dangaard Brouer <hawk@...nel.org>
>
> > Fixes: 3d76a4d3d4e5 ("bpf: XDP metadata RX kfuncs")
> > Reported-by: Stanislav Fomichev <sdf@...gle.com>
> > Closes: https://lore.kernel.org/bpf/ZKWo0BbpLfkZHbyE@google.com/
> > Signed-off-by: Larysa Zaremba <larysa.zaremba@...el.com>

Acked-by: Stanislav Fomichev <sdf@...gle.com>

Thank you for the fix!

> > ---
> >   net/core/xdp.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/core/xdp.c b/net/core/xdp.c
> > index 41e5ca8643ec..8362130bf085 100644
> > --- a/net/core/xdp.c
> > +++ b/net/core/xdp.c
> > @@ -741,7 +741,7 @@ __bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32 *hash,
> >   __diag_pop();
> >
> >   BTF_SET8_START(xdp_metadata_kfunc_ids)
> > -#define XDP_METADATA_KFUNC(_, name) BTF_ID_FLAGS(func, name, 0)
> > +#define XDP_METADATA_KFUNC(_, name) BTF_ID_FLAGS(func, name, KF_TRUSTED_ARGS)
> >   XDP_METADATA_KFUNC_xxx
> >   #undef XDP_METADATA_KFUNC
> >   BTF_SET8_END(xdp_metadata_kfunc_ids)
>