On Mon, Mar 15, 2021 at 3:41 PM Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx> wrote: > > On 15/03/2021 11:52, Dmitry Vyukov wrote: > > On Mon, Mar 15, 2021 at 12:30 PM Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx> wrote: > >> > >> On 14/03/2021 11:03, Dmitry Vyukov wrote: > >>> On Sun, Mar 14, 2021 at 11:01 AM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > >>>>> On Wed, Mar 10, 2021 at 7:28 PM syzbot > >>>>> <syzbot+c23c5421600e9b454849@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > >>>>>> > >>>>>> Hello, > >>>>>> > >>>>>> syzbot found the following issue on: > >>>>>> > >>>>>> HEAD commit: 0d7588ab riscv: process: Fix no prototype for arch_dup_tas.. > >>>>>> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git fixes > >>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=122c343ad00000 > >>>>>> kernel config: https://syzkaller.appspot.com/x/.config?x=e3c595255fb2d136 > >>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=c23c5421600e9b454849 > >>>>>> userspace arch: riscv64 > >>>>>> > >>>>>> Unfortunately, I don't have any reproducer for this issue yet. > >>>>>> > >>>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit: > >>>>>> Reported-by: syzbot+c23c5421600e9b454849@xxxxxxxxxxxxxxxxxxxxxxxxx > >>>>> > >>>>> +riscv maintainers > >>>>> > >>>>> Another case of put_user crashing. > >>>> > >>>> There are 58 crashes in sock_ioctl already. Somehow there is a very > >>>> significant skew towards crashing with this "user memory without > >>>> uaccess routines" in schedule_tail and sock_ioctl of all places in the > >>>> kernel that use put_user... This looks very strange... Any ideas > >>>> what's special about these 2 locations? > >>> > >>> I could imagine if such a crash happens after a previous stack > >>> overflow and now task data structures are corrupted. But f_getown does > >>> not look like a function that consumes way more than other kernel > >>> syscalls... > >> > >> The last crash I looked at suggested somehow put_user got re-entered > >> with the user protection turned back on. Either there is a path through > >> one of the kernel handlers where this happens or there's something > >> weird going on with qemu. > > > > Is there any kind of tracking/reporting that would help to localize > > it? I could re-reproduce with that code. > > I'm not sure. I will have a go at debugging on qemu today just to make > sure I can reproduce here before I have to go into the office and fix > my Icicle board for real hardware tests. > > I think my first plan post reproduction is to stuff some trace points > into the fault handlers to see if we can get a idea of faults being > processed, etc. > > Maybe also add a check in the fault handler to see if the fault was > in a fixable region and post an error if that happens / maybe retry > the instruction with the relevant SR_SUM flag set. > > Hopefully tomorrow I can get a run on real hardware to confirm. > Would have been better if the Unmatched board I ordered last year > would turn up. In retrospect it's obvious what's common between these 2 locations: they both call a function inside of put_user. #syz dup: BUG: unable to handle kernel access to user memory in schedule_tail
