netdev - Re: [offlist] Re: Crash in netlink/sk_filter_trim

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Message-ID: <CALeDE9NYxp34Dx_fZ66=7XQ5u7grm-UU=LisR3EDfTF8vYUctw@mail.gmail.com>
Date:   Fri, 17 Aug 2018 22:15:01 +0100
From:   Peter Robinson <pbrobinson@...il.com>
To:     Stefan Wahren <stefan.wahren@...e.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        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>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [offlist] Re: Crash in netlink/sk_filter_trim_cap on ARMv7 on 4.18rc1

Hi Stefan,

>> 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.

Would be fab to get that into the kernel so this is widely tested
moving forward.

Peter