From: Daniel Borkmann <daniel@iogearbox•net>
To: Tycho Andersen <tycho.andersen@canonical•com>,
Alexei Starovoitov <ast@kernel•org>,
"David S. Miller" <davem@davemloft•net>
Cc: netdev@vger•kernel.org
Subject: Re: [PATCH] ebpf: emit correct src_reg for conditional jumps
Date: Fri, 11 Sep 2015 10:45:29 +0200 [thread overview]
Message-ID: <55F294A9.9020005@iogearbox.net> (raw)
In-Reply-To: <1441931107-17673-1-git-send-email-tycho.andersen@canonical.com>
On 09/11/2015 02:25 AM, Tycho Andersen wrote:
> Instead of always emitting BPF_REG_X, let's emit BPF_REG_X only when the
> source actually is BPF_X. This causes programs generated by the classic
> converter to not be importable via bpf(), as the eBPF verifier checks that
> the src_reg is correct or 0. While not a problem yet, this will be a
> problem when BPF_PROG_DUMP lands, and we can potentially dump and re-import
> programs generated by the converter.
>
> Signed-off-by: Tycho Andersen <tycho.andersen@canonical•com>
> CC: Alexei Starovoitov <ast@kernel•org>
> CC: Daniel Borkmann <daniel@iogearbox•net>
I think the description at the beginning could have been a bit clearer. I.e.
it's safe to zero insn->src_reg for BPF_SRC(fp->code) that is not X, because
we can either have X or K for classic jump compares, and in case of K we're
only interested in the immediate value, but not a possible src_reg, of course,
so eBPF converter should have zeroed it.
Yeah, it was never really the aim of the converter to cover something like
that requirement you seem to have:
load classic BPF
-> transform into eBPF
-> dump that eBPF result to uspace
-> load that eBPF via bpf(2)
Anyway, it doesn't cause an issue in the current code as stated, but it's good
if we fix it up nevertheless.
Looks good to me:
Acked-by: Daniel Borkmann <daniel@iogearbox•net>
next prev parent reply other threads:[~2015-09-11 8:45 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-11 0:25 [PATCH] ebpf: emit correct src_reg for conditional jumps Tycho Andersen
2015-09-11 8:45 ` Daniel Borkmann [this message]
2015-09-11 9:28 ` Daniel Borkmann
2015-09-11 15:40 ` Alexei Starovoitov
2015-09-11 15:50 ` Tycho Andersen
2015-09-11 16:53 ` Daniel Borkmann
2015-09-11 21:53 ` David Miller
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