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

On 08/17/2018 02:25 PM, Peter Robinson wrote:

On Thu, Aug 16, 2018 at 11:58 PM, Russell King - ARM Linux
[off-list ref] wrote:

quoted

On Thu, Aug 16, 2018 at 10:35:16PM +0200, Marc Haber wrote:

quoted

On Mon, Jun 25, 2018 at 05:41:27PM +0100, Peter Robinson wrote:

quoted

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.

[1] git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

quoted

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?

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