Re: qemu-arm64: Unexpected kernel BRK exception at EL1 - WARNING: CPU: 3 PID: 0 at kernel/context_tracking.c:128 ct_kernel_exit.constprop

[Mark Rutland]

On Mon, Jul 03, 2023 at 12:03:38PM +0200, Arnd Bergmann wrote:
> On Mon, Jul 3, 2023, at 11:51, Mark Rutland wrote:
> > On Mon, Jul 03, 2023 at 12:02:22PM +0530, Naresh Kamboju wrote:
> >> On Sun, 2 Jul 2023 at 13:56, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> >> > On Sat, Jul 1, 2023, at 10:42, Naresh Kamboju wrote:
> >> >
> >> 
> >> Here is the build artifacts location with kselftest merge configs.
> >> https://storage.tuxsuite.com/public/linaro/lkft/builds/2Rum1V78RQJMftEanwtN28dApDO/
> >
> > In your .config here, I note you have:
> >
> > | CONFIG_UBSAN_TRAP=y
> >
> > Can you try this with CONFIG_UBSAN_TRAP=n ?
> >
> >> [   56.150153] Modules linked in: crct10dif_ce sm3_ce sm3 sha3_ce
> >> sha512_ce sha512_arm64 cfg80211 bluetooth rfkill sch_fq_codel fuse drm
> >> [   56.151781] CPU: 0 PID: 438 Comm: seccomp_bpf Not tainted 6.4.0 #1
> >> [   56.152043] Hardware name: linux,dummy-virt (DT)
> >> [   56.152396] pstate: 41400005 (nZcv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
> >> [   56.152667] pc : alloc_pid+0x3b4/0x3c8
> >> [   56.154243] lr : alloc_pid+0x140/0x3c8
> >
> > Looking at objdump, that's:
> >
> > | ffff8000800d73b0 <alloc_pid>:
> > | ...
> > | ffff8000800d7764:       d4207d00        brk     #0x3e8
> >
> > ... and addr2line fingers this as:
> >
> > | [mark@lakrids:~/tmp-naresh-kamboju]% usekorg 10.3.0 
> > aarch64-linux-addr2line -ife vmlinux ffff8000800d7764                   
> >        
> > | alloc_pid
> > | /builds/linux/kernel/pid.c:244
> >
> > ... which appears to be:
> >
> > | 244                 pid->numbers[i].nr = nr;
> >
> > Full objdump of the function below; as above I suspect this is UBSAN triggering
> > a __builtin_trap() on an out-of-range access.
> 
> It looks like a fix has already made it into mainline now, so it
> should be fixed on the latest linux-next:
> 
> https://lore.kernel.org/lkml/20230630180418.gonna.286-kees@xxxxxxxxxx/

Thanks for the pointer!

Mark.