netdev - Re: [offlist] Re: Crash in netlink/sk_filter_trim_cap on ARMv7 on 4.18rc1

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Date:   Fri, 17 Aug 2018 20:51:29 +0200 (CEST)
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Marc Haber <mh+netdev@...schlus.de>, labbott@...hat.com,
        Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Peter Robinson <pbrobinson@...il.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [offlist] Re: Crash in netlink/sk_filter_trim_cap on ARMv7 on
 4.18rc1

Hi Daniel,

> Daniel Borkmann <daniel@...earbox.net> hat am 17. August 2018 um 20:30 geschrieben:
> 
> 
> On 08/17/2018 06:17 PM, Russell King - ARM Linux wrote:
> > On Fri, Aug 17, 2018 at 02:40:19PM +0200, Daniel Borkmann wrote:
> >> I'd have one potential bug suspicion, for the 4.18 one you were trying,
> >> could you run with the below patch to see whether it would help?
> > 
> > I think this is almost certainly the problem - looking at the history,
> > it seems that the "-4" was assumed to be part of the scratch stuff in
> > commit 38ca93060163 ("bpf, arm32: save 4 bytes of unneeded stack space")
> > but it isn't - it's because "off" of zero refers to the top word in the
> > stack (iow at STACK_SIZE-4).
> 
> Yeah agree, my thinking as well (albeit bit late, sigh, sorry about that).
> Waiting for Peter to get back with results for definite confirmation. Your
> rework in 1c35ba122d4a ("ARM: net: bpf: use negative numbers for stacked
> registers") and 96cced4e774a ("ARM: net: bpf: access eBPF scratch space using
> ARM FP register") fixes this in mainline, so unless I'm missing something this
> would only need a stand-alone fix for 4.18/stable which I can cook up and
> submit then.

i was able to reproduce this issue on RPi 3 with Linux 4.18.1 + multi_v7_defconfig and the following  config changes:

 --- a/arch/arm/configs/multi_v7_defconfig
+++ b/arch/arm/configs/multi_v7_defconfig
@@ -2,7 +2,10 @@ CONFIG_SYSVIPC=y
 CONFIG_NO_HZ=y
 CONFIG_HIGH_RES_TIMERS=y
 CONFIG_CGROUPS=y
+CONFIG_CGROUP_BPF=y
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_BPF_SYSCALL=y
+CONFIG_BPF_JIT_ALWAYS_ON=y
 CONFIG_EMBEDDED=y
 CONFIG_PERF_EVENTS=y
 CONFIG_MODULES=y
@@ -153,6 +156,8 @@ CONFIG_IPV6_MIP6=m
 CONFIG_IPV6_TUNNEL=m
 CONFIG_IPV6_MULTIPLE_TABLES=y
 CONFIG_NET_DSA=m
+CONFIG_BPF_JIT=y
+CONFIG_BPF_STREAM_PARSER=y
 CONFIG_CAN=y
 CONFIG_CAN_AT91=m
 CONFIG_CAN_FLEXCAN=m

After applying the "-4" patch the oopses doesn't appear during boot anymore.

Stefan

> 
> Thanks,
> Daniel
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel


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