Date:   Fri, 17 Aug 2018 15:32:22 +0100
From:   Peter Robinson <pbrobinson@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        Marc Haber <mh+netdev@...schlus.de>,
        linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
        labbott@...hat.com, Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [offlist] Re: Crash in netlink/sk_filter_trim_cap on ARMv7 on 4.18rc1

On Fri, Aug 17, 2018 at 1:40 PM, Daniel Borkmann <daniel@...earbox.net> wrote:
> On 08/17/2018 02:25 PM, Peter Robinson wrote:
>> On Thu, Aug 16, 2018 at 11:58 PM, Russell King - ARM Linux
>> <linux@...linux.org.uk> wrote:
>>> On Thu, Aug 16, 2018 at 10:35:16PM +0200, Marc Haber wrote:
>>>> On Mon, Jun 25, 2018 at 05:41:27PM +0100, Peter Robinson wrote:
>>>>> So with that and the other fix there was no improvement, with those
>>>>> and the BPF JIT disabled it works, I'm not sure if the two patches
>>>>> have any effect with the JIT disabled though.
>>>>
>>>> I can confirm the crash with the released 4.18.1 on Banana Pi, and I can
>>>> also confirm that disabling BPF JIT makes the Banana Pi work again.,
>>>
>>> I'm afraid that the information in the crash dumps is insufficient
>>> to be able to work very much out about these crashes.
>>>
>>> We need a recipe (kernel configuration and what userspace is doing)
>>> so that it's possible to recreate the crash, or we need responses
>>> to requests for information - I requested the disassembly of
>>> sk_filter_trim_cap and the BPF code dump via setting a sysctl back
>>> in early July.  Without this, as I say, I don't see how this problem
>>> can be progressed.
>>
>> I can provide a kernel config [1] but I've not had enough time to sit
>> down and get the rest of the stuff and debug it due to a combination
>> of travel and other priorities.
>
> Did you get a chance to try latest kernel from Linus' tree [1] from last
> few days to see whether the issue is still persistent? There have been
> a number of improvements, bit strange why e.g. Russell didn't run into
> it while others have, hmm. Perhaps due to EABI vs non EABI.

I haven't had a chance to try anything from the 4.19 merge window as
yet, I'm traveling this week so it was on the list for next week to
try.

> [1] git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>
>>> If the problem is at boot, one way to set the sysctl would be to
>>> hack the kernel and explicitly initialise the sysctl to '2', or
>>> boot with init=/bin/sh, then manually mount /proc, set the sysctl,
>>> and then "exec /sbin/init" from that shell.  (Remember there's no
>>> job control in that shell, so ^z, ^c, etc do not work.)
>>
>> It starts to happen in the early kernel boot long before we get to any
>> userspace across a number of ARMv7 devices (RPi2/3, BeagleBone and
>> AllWinner H3 based devices at least).
>>
>> [1] https://pbrobinson.fedorapeople.org/kernel-armv7hl.config
>
> 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 will try and get someone to test that today, thanks

> Thanks,
> Daniel
>
> diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
> index f6a62ae..c864f6b 100644
> --- a/arch/arm/net/bpf_jit_32.c
> +++ b/arch/arm/net/bpf_jit_32.c
> @@ -238,7 +238,7 @@ static void jit_fill_hole(void *area, unsigned int size)
>  #define STACK_SIZE     ALIGN(_STACK_SIZE, STACK_ALIGNMENT)
>
>  /* Get the offset of eBPF REGISTERs stored on scratch space. */
> -#define STACK_VAR(off) (STACK_SIZE - off)
> +#define STACK_VAR(off) (STACK_SIZE - off - 4)
>
>  #if __LINUX_ARM_ARCH__ < 7
>

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