On Thu, Mar 18, 2021 at 4:35 PM Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx> wrote: > > On 18/03/2021 15:18, Dmitry Vyukov wrote: > > 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 > > I think so. I've posted a patch that you can test, which should force > the flags to be saved over switch_to(). I think the sanitisers are just > making it easier to see. > > There is a seperate issue of passing complicated things to put_user() > as for security, the function may be executed with the user-space > protections turned off. I plan to raise this on the kernel list later > once I've done some more testing. Thanks for quick debugging and the fix. This is the top crasher on the syzbot instance, so this will unblock real testing. I think I will trust your testing. syzbot instance is now on riscv/fixes branch, so it will pick it up as soon as it's in that tree (hopefully soon) and will do as exhaustive testing as possible :)
