On Thu, Jan 11, 2024 at 9:13 PM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > On Thu, Jan 11, 2024 at 1:06 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > > > > On 11.01.24 22:04, Suren Baghdasaryan wrote: > > > On Thu, Jan 11, 2024 at 9:00 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > > >> > > >> On 11.01.24 21:20, Suren Baghdasaryan wrote: > > >>> On Thu, Jan 11, 2024 at 6:58 PM David Hildenbrand <david@xxxxxxxxxx> wrote: > > >>>> > > >>>> On 11.01.24 19:34, Suren Baghdasaryan wrote: > > >>>>> On Thu, Jan 11, 2024 at 8:44 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > >>>>>> > > >>>>>> On Thu, Jan 11, 2024 at 8:40 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > >>>>>>> > > >>>>>>> On Thu, Jan 11, 2024 at 8:25 AM syzbot > > >>>>>>> <syzbot+705209281e36404998f6@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > >>>>>>>> > > >>>>>>>> Hello, > > >>>>>>>> > > >>>>>>>> syzbot found the following issue on: > > >>>>>>>> > > >>>>>>>> HEAD commit: e2425464bc87 Add linux-next specific files for 20240105 > > >>>>>>>> git tree: linux-next > > >>>>>>>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14941cdee80000 > > >>>>>>>> kernel config: https://syzkaller.appspot.com/x/.config?x=4056b9349f3da8c9 > > >>>>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=705209281e36404998f6 > > >>>>>>>> compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 > > >>>>>>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=125d0a09e80000 > > >>>>>>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15bc7331e80000 > > >>>>>>>> > > >>>>>>>> Downloadable assets: > > >>>>>>>> disk image: https://storage.googleapis.com/syzbot-assets/2f738185e2cf/disk-e2425464.raw.xz > > >>>>>>>> vmlinux: https://storage.googleapis.com/syzbot-assets/b248fcf4ea46/vmlinux-e2425464.xz > > >>>>>>>> kernel image: https://storage.googleapis.com/syzbot-assets/a9945c8223f4/bzImage-e2425464.xz > > >>>>>>>> > > >>>>>>>> The issue was bisected to: > > >>>>>>>> > > >>>>>>>> commit adef440691bab824e39c1b17382322d195e1fab0 > > >>>>>>>> Author: Andrea Arcangeli <aarcange@xxxxxxxxxx> > > >>>>>>>> Date: Wed Dec 6 10:36:56 2023 +0000 > > >>>>>>>> > > >>>>>>>> userfaultfd: UFFDIO_MOVE uABI > > >>>>>>>> > > >>>>>>>> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=11cb6ea9e80000 > > >>>>>>>> final oops: https://syzkaller.appspot.com/x/report.txt?x=13cb6ea9e80000 > > >>>>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=15cb6ea9e80000 > > >>>>>>>> > > >>>>>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit: > > >>>>>>>> Reported-by: syzbot+705209281e36404998f6@xxxxxxxxxxxxxxxxxxxxxxxxx > > >>>>>>>> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") > > >>>>>>>> > > >>>>>>>> do_one_initcall+0x128/0x680 init/main.c:1237 > > >>>>>>>> do_initcall_level init/main.c:1299 [inline] > > >>>>>>>> do_initcalls init/main.c:1315 [inline] > > >>>>>>>> do_basic_setup init/main.c:1334 [inline] > > >>>>>>>> kernel_init_freeable+0x692/0xc30 init/main.c:1552 > > >>>>>>>> kernel_init+0x1c/0x2a0 init/main.c:1442 > > >>>>>>>> ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147 > > >>>>>>>> ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242 > > >>>>>>>> ------------[ cut here ]------------ > > >>>>>>>> kernel BUG at include/linux/page-flags.h:1035! > > >>>>>>>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN > > >>>>>>>> CPU: 0 PID: 5068 Comm: syz-executor191 Not tainted 6.7.0-rc8-next-20240105-syzkaller #0 > > >>>>>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023 > > >>>>>>>> RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline] > > >>>>>>> > > >>>>>>> From a quick look, I think the new ioctl is being used against a > > >>>>>>> file-backed page and that's why PageAnonExclusive() throws this error. > > >>>>>>> I'll confirm if this is indeed the case and will add checks for that > > >>>>>>> case. Thanks! > > >>>>>> > > >>>>>> Hmm. Looking at the reproducer it does not look like a file-backed > > >>>>>> memory... Anyways, I'm on it. > > >>>>> > > >>>>> Looks like the test is trying to move the huge_zero_page. Wonder how > > >>>>> we should handle this. Just fail or do something else? Adding David > > >>>>> and Peter for feedback. > > >>>> > > >>>> You'll need some special-casing to handle that. But it should be fairly > > >>>> easy. > > >>> > > >>> Ok, so should we treat zeropage the same as PAE and map destination > > >>> PTE/PMD to zeropage while clearing source PTE/PMD? > > >> > > >> Likely yes. So it's transparent for user space what we are moving. (this > > >> sounds like an easy case to not require a prior write access just to > > >> move it) > > > > > > Ok, working on it. split_huge_pmd() already knows how to split > > > huge_zero_page but I think I'll need special handling in both > > > move_pages_pte() and move_pages_huge_pmd(). > > > > A PTE-mapped huge zeropage is just a page table populated with the > > ordinary shared zeropage. Are you moving the ordinary shared zeropage as > > well? If not, you should do so for consistency (or not do either :) ). > > Yes, I think I should move ordinary zeropages as well. I have a version that seems to work but I want to test it more and it's too heavy to be considered a quick fix for linux-next. I'll post a simple one-line fix which takes care of this crash and keeps the behavior for zeropages the same (ioctl returns -EBUSY). Later will post a separate patch to move huge and ordinary zeropages. > > > > > -- > > Cheers, > > > > David / dhildenb > >
