[bug report] Bug: Write fault blocked by KUAP!

[Ming Lei]

On Thu, Feb 26, 2026 at 6:48 PM Ming Lei <ming.lei at redhat.com> wrote:
>
> Hi Changhui,
>
> Thanks for the report!
>
> Loop Caleb Sander Mateos  in.
>
> Thanks,
>
> On Thu, Feb 26, 2026 at 6:37 PM Changhui Zhong <czhong at redhat.com> wrote:
> >
> > Hello,
> >
> > on the ppc64le arch, I hit the issue below with ublksrv on the latest
> > linux-block/for-next, please help check it, and let me know if you
> > need any info/test for it. Thanks.
> >
> > INFO: HEAD of cloned kernel
> > commit 37a43fd770f3dcac8f72f3ea909b3e893e2385c9
> > Merge: 13cd9b41227a c1dfbd7e71b0
> > Author: Jens Axboe <axboe at kernel.dk>
> > Date:   Wed Feb 25 08:37:06 2026 -0700
> >
> >     Merge branch 'for-7.1/block' into for-next
> >
> >     * for-7.1/block:
> >       ublk: report BLK_SPLIT_INTERVAL_CAPABLE
> >
> > reproducer:
> > compile and install https://github.com/ublk-org/ublksrv.git
> > #echo 0 > /proc/sys/kernel/io_uring_disabled
> > #modprobe ublk_drv
> > #cd ublksrv
> > #make test T=null
> > #make test T=loop
> >
> > dmesg log：
> > Feb 26 00:24:30 ibm-p9z-27-lp26 journal: running null/002
> > Feb 26 00:24:30 ibm-p9z-27-lp26 ublksrvd-0[57921]: start ublksrv io
> > daemon ublksrvd-0
> > Feb 26 00:24:30 ibm-p9z-27-lp26 ublksrvd-0[57921]: tid 57923: ublk dev
> > 0 queue 0 started
> > Feb 26 00:24:30 ibm-p9z-27-lp26 ublksrvd-0[57921]: tid 57924: ublk dev
> > 0 queue 1 started
> > Feb 26 00:24:36 ibm-p9z-27-lp26 NetworkManager[818]: <warn>
> > [1772083476.4882] platform-linux: do-add-ip6-address[2:
> > fe80::8448:a3ff:fe51:f102]: failure 13 (Permission denied - ipv6: IPv6
> > is disabled on this device)
> > Feb 26 00:24:36 ibm-p9z-27-lp26 NetworkManager[818]: <warn>
> > [1772083476.4885] platform-linux: do-add-ip6-address[2:
> > 2620:52:9:160c:8448:a3ff:fe51:f102]: failure 13 (Permission denied -
> > ipv6: IPv6 is disabled on this device)
> > Feb 26 00:24:36 ibm-p9z-27-lp26 NetworkManager[818]: <warn>
> > [1772083476.4938] l3cfg[0f1985ec14299e62,ifindex=2]: unable to
> > configure IPv6 route: type unicast fe80::/64 dev 2 metric 1024 mss 0
> > rt-src ipv6ll
> > Feb 26 00:24:38 ibm-p9z-27-lp26 NetworkManager[818]: <warn>
> > [1772083478.4938] ipv6ll[95ab7f3fdbfe643d,ifindex=2]: changed: no IPv6
> > link local address to retry after Duplicate Address Detection failures
> > (back off)
> > Feb 26 00:24:38 ibm-p9z-27-lp26 NetworkManager[818]: <warn>
> > [1772083478.4943] platform-linux: do-add-ip6-address[2:
> > 2620:52:9:160c:8448:a3ff:fe51:f102]: failure 13 (Permission denied -
> > ipv6: IPv6 is disabled on this device)
> > Feb 26 00:24:48 ibm-p9z-27-lp26 NetworkManager[818]: <warn>
> > [1772083488.5034] platform-linux: do-add-ip6-address[2:
> > fe80::8448:a3ff:fe51:f102]: failure 13 (Permission denied - ipv6: IPv6
> > is disabled on this device)
> > Feb 26 00:24:48 ibm-p9z-27-lp26 NetworkManager[818]: <warn>
> > [1772083488.5037] platform-linux: do-add-ip6-address[2:
> > 2620:52:9:160c:8448:a3ff:fe51:f102]: failure 13 (Permission denied -
> > ipv6: IPv6 is disabled on this device)
> > Feb 26 00:24:48 ibm-p9z-27-lp26 NetworkManager[818]: <warn>
> > [1772083488.5041] l3cfg[0f1985ec14299e62,ifindex=2]: unable to
> > configure IPv6 route: type unicast fe80::/64 dev 2 metric 1024 mss 0
> > rt-src ipv6ll
> > Feb 26 00:24:50 ibm-p9z-27-lp26 NetworkManager[818]: <warn>
> > [1772083490.5034] ipv6ll[95ab7f3fdbfe643d,ifindex=2]: changed: no IPv6
> > link local address to retry after Duplicate Address Detection failures
> > (back off)
> > Feb 26 00:24:50 ibm-p9z-27-lp26 NetworkManager[818]: <warn>
> > [1772083490.5039] platform-linux: do-add-ip6-address[2:
> > 2620:52:9:160c:8448:a3ff:fe51:f102]: failure 13 (Permission denied -
> > ipv6: IPv6 is disabled on this device)
> > Feb 26 00:24:58 ibm-p9z-27-lp26 kernel: Kernel attempted to read user
> > page (7fff81210000) - exploit attempt? (uid: 0)
> > Feb 26 00:24:58 ibm-p9z-27-lp26 kernel: ------------[ cut here ]------------
> > Feb 26 00:24:58 ibm-p9z-27-lp26 kernel: Bug: Read fault blocked by KUAP!
> > Feb 26 00:24:58 ibm-p9z-27-lp26 kernel: WARNING:
> > arch/powerpc/mm/fault.c:231 at bad_kernel_fault.isra.0+0xc8/0x2c0,
> > CPU#5: lt-ublk.null/57924

oops, it shouldn't be related with `ublk: report BLK_SPLIT_INTERVAL_CAPABLE`,
Perhaps one issue lies in the ppcle64 architecture code.

I will find one ppc box and try to reproduce this.

Thanks,