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

[Caleb Sander Mateos]

On Thu, Feb 26, 2026 at 4:44 AM Ming Lei <ming.lei at redhat.com> wrote:
>
> 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.

Agreed, the "Kernel attempted to read user page" error seems
incorrect. The call trace shows this is in copy_from_iter(), so
reading a user page is expected. I too would be suspicious of the
powerpc copy_from_iter() implementation.

Best,
Caleb