From: John Fastabend <john.fastabend@gmail.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>, davem@davemloft.net
Cc: daniel@iogearbox.net, netdev@vger.kernel.org,
bpf@vger.kernel.org, kernel-team@fb.com
Subject: RE: [PATCH v2 bpf-next 1/3] bpf: Support for pointers beyond pkt_end.
Date: Thu, 12 Nov 2020 11:16:11 -0800 [thread overview]
Message-ID: <5fad89fb649af_2a612088e@john-XPS-13-9370.notmuch> (raw)
In-Reply-To: <20201111031213.25109-2-alexei.starovoitov@gmail.com>
Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@kernel.org>
>
> This patch adds the verifier support to recognize inlined branch conditions.
> The LLVM knows that the branch evaluates to the same value, but the verifier
> couldn't track it. Hence causing valid programs to be rejected.
> The potential LLVM workaround: https://reviews.llvm.org/D87428
> can have undesired side effects, since LLVM doesn't know that
> skb->data/data_end are being compared. LLVM has to introduce extra boolean
> variable and use inline_asm trick to force easier for the verifier assembly.
>
> Instead 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".
> }
>
> Tested-by: Jiri Olsa <jolsa@redhat.com>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---
> include/linux/bpf_verifier.h | 2 +-
> kernel/bpf/verifier.c | 129 +++++++++++++++++++++++++++++------
> 2 files changed, 108 insertions(+), 23 deletions(-)
>
Thanks, we can remove another set of inline asm logic.
Acked-by: John Fastabend <john.fastabend@gmail.com>
> if (pred >= 0) {
> @@ -7517,7 +7601,8 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
> */
> if (!__is_pointer_value(false, dst_reg))
> err = mark_chain_precision(env, insn->dst_reg);
> - if (BPF_SRC(insn->code) == BPF_X && !err)
> + if (BPF_SRC(insn->code) == BPF_X && !err &&
> + !__is_pointer_value(false, src_reg))
This could have been more specific with !type_is_pkt_pointer() correct? I
think its fine as is though.
> err = mark_chain_precision(env, insn->src_reg);
> if (err)
> return err;
> --
> 2.24.1
>
next prev parent reply other threads:[~2020-11-12 19:16 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-11 3:12 [PATCH v2 bpf-next 0/3] bpf: Pointers beyond packet end Alexei Starovoitov
2020-11-11 3:12 ` [PATCH v2 bpf-next 1/3] bpf: Support for pointers beyond pkt_end Alexei Starovoitov
2020-11-12 19:16 ` John Fastabend [this message]
2020-11-12 23:56 ` Daniel Borkmann
2020-11-13 0:09 ` Alexei Starovoitov
2020-11-13 0:50 ` Daniel Borkmann
2020-11-12 23:59 ` Alexei Starovoitov
2020-11-13 0:35 ` John Fastabend
2020-11-11 3:12 ` [PATCH v2 bpf-next 2/3] selftests/bpf: Add skb_pkt_end test Alexei Starovoitov
2020-11-12 19:19 ` John Fastabend
2020-11-11 3:12 ` [PATCH v2 bpf-next 3/3] selftests/bpf: Add asm tests for pkt vs pkt_end comparison Alexei Starovoitov
2020-11-12 19:24 ` John Fastabend
2021-01-20 20:51 ` Jiri Olsa
2020-11-13 0:50 ` [PATCH v2 bpf-next 0/3] bpf: Pointers beyond packet end patchwork-bot+netdevbpf
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