netdev - Re: [PATCH bpf-next 0/3] bpf: Pointers beyond packet end.

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Message-ID: <20201022094758.GC2318292@krava>
Date:   Thu, 22 Oct 2020 11:47:58 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     davem@...emloft.net, daniel@...earbox.net,
        john.fastabend@...il.com, jolsa@...nel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH bpf-next 0/3] bpf: Pointers beyond packet end.

On Wed, Oct 21, 2020 at 11:20:12AM -0700, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@...nel.org>
> 
> In some cases LLVM uses the knowledge that branch is taken to optimze the code
> which causes the verifier to reject valid programs.
> Teach the verifier to recognize that
> r1 = skb->data;
> r1 += 10;
> r2 = skb->data_end;
> if (r1 > r2) {
>   here r1 points beyond packet_end and subsequent
>   if (r1 > r2) // always evaluates to "true".
> }
> 
> Alexei Starovoitov (3):
>   bpf: Support for pointers beyond pkt_end.
>   selftests/bpf: Add skb_pkt_end test
>   selftests/bpf: Add asm tests for pkt vs pkt_end comparison.

Tested-by: Jiri Olsa <jolsa@...hat.com>

thanks,
jirka

> 
>  include/linux/bpf_verifier.h                  |   2 +-
>  kernel/bpf/verifier.c                         | 131 +++++++++++++++---
>  .../bpf/prog_tests/test_skb_pkt_end.c         |  41 ++++++
>  .../testing/selftests/bpf/progs/skb_pkt_end.c |  54 ++++++++
>  .../testing/selftests/bpf/verifier/ctx_skb.c  |  42 ++++++
>  5 files changed, 247 insertions(+), 23 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/test_skb_pkt_end.c
>  create mode 100644 tools/testing/selftests/bpf/progs/skb_pkt_end.c
> 
> -- 
> 2.23.0
>