linux-kernel - Re: kernel crash in bpf_jit on x86

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Date:	Fri, 10 Oct 2014 14:17:45 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: kernel crash in bpf_jit on x86_64 when running nmap

On Fri, Oct 10, 2014 at 1:44 PM, Darrick J. Wong
<darrick.wong@...cle.com> wrote:
> Hi everyone,
>
> I was running nmap on a x86_64 qemu guest and experienced the following crash:
>
> # nmap -sS -O -vvv 192.168.122.1
> Starting Nmap 6.40 ( http://nmap.org ) at 2014-10-10 13:14 PDT
> Initiating ARP Ping Scan at 13:14
> Scanning 192.168.122.1 [1 port]
> <kaboom>
>
> dmesg output is as follows (I set net.core.bpf_jit_enable=2 the second time):
>
> [   32.376291] flen=3 proglen=82 pass=0 image=ffffffffc01ac65b
> [   32.377595] JIT code: 00000000: 55 48 89 e5 48 81 ec 28 02 00 00 48 89 9d d8 fd
> [   32.379243] JIT code: 00000010: ff ff 4c 89 ad e0 fd ff ff 4c 89 b5 e8 fd ff ff
> [   32.380984] JIT code: 00000020: 4c 89 bd f0 fd ff ff 31 c0 4d 31 ed 48 89 fb b8
> [   32.382606] JIT code: 00000030: 00 00 00 00 48 8b 9d d8 fd ff ff 4c 8b ad e0 fd
> [   32.384280] JIT code: 00000040: ff ff 4c 8b b5 e8 fd ff ff 4c 8b bd f0 fd ff ff
> [   32.385911] JIT code: 00000050: c9 c3
> [   32.386841] bpf_jit: proglen=265 != oldproglen=269

thanks for the report. The line above indicates that JIT tried to emit
4 byte longer program than during pre-final pass.
Will look at it asap.
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