Hi Vlastimil, Sorry for the late answer I got a few day off. On 31/10/2017 14:57, Vlastimil Babka wrote: > +CC Andrea, Thorsten, Linus > > On 10/31/2017 02:20 PM, Vlastimil Babka wrote: >> On 10/31/2017 01:42 PM, Dmitry Vyukov wrote: >>>> My vm_area_struct is 192 bytes, could be your layout is different due to >>>> .config. At offset 80 I have vma->vm_flags. That is checked by >>>> __do_page_fault(), but only after vma->vm_start (offset 0). Of course, >>>> reordering is possible. >>> >>> >>> It seems that compiler over-optimizes things and messes debug info. >>> I just re-reproduced this on upstream >>> 15f859ae5c43c7f0a064ed92d33f7a5bc5de6de0 and got the same report: >>> >>> ================================================================== >>> BUG: KASAN: use-after-free in arch_local_irq_enable >>> arch/x86/include/asm/paravirt.h:787 [inline] >>> BUG: KASAN: use-after-free in __do_page_fault+0xc03/0xd60 >>> arch/x86/mm/fault.c:1357 >>> Read of size 8 at addr ffff880064d19aa0 by task syz-executor/8001 >>> >>> CPU: 0 PID: 8001 Comm: syz-executor Not tainted 4.14.0-rc6+ #12 >>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 >>> Call Trace: >>> __dump_stack lib/dump_stack.c:16 [inline] >>> dump_stack+0x194/0x257 lib/dump_stack.c:52 >>> print_address_description+0x73/0x250 mm/kasan/report.c:252 >>> kasan_report_error mm/kasan/report.c:351 [inline] >>> kasan_report+0x25b/0x340 mm/kasan/report.c:409 >>> __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430 >>> arch_local_irq_enable arch/x86/include/asm/paravirt.h:787 [inline] >>> __do_page_fault+0xc03/0xd60 arch/x86/mm/fault.c:1357 >>> do_page_fault+0xee/0x720 arch/x86/mm/fault.c:1520 >>> do_async_page_fault+0x82/0x110 arch/x86/kernel/kvm.c:273 >>> async_page_fault+0x22/0x30 arch/x86/entry/entry_64.S:1069 >>> RIP: 0033:0x441bd0 >>> RSP: 002b:00007f2ed8229798 EFLAGS: 00010202 >>> RAX: 00007f2ed82297c0 RBX: 0000000000000000 RCX: 000000000000000e >>> RDX: 0000000000000400 RSI: 0000000020012fe0 RDI: 00007f2ed82297c0 >>> RBP: 0000000000748020 R08: 0000000000000400 R09: 0000000000000000 >>> R10: 0000000020012fee R11: 0000000000000246 R12: 00000000ffffffff >>> R13: 0000000000008430 R14: 00000000006ec4d0 R15: 00007f2ed822a700 >>> >>> Allocated by task 8001: >>> save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 >>> save_stack+0x43/0xd0 mm/kasan/kasan.c:447 >>> set_track mm/kasan/kasan.c:459 [inline] >>> kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551 >>> kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489 >>> kmem_cache_alloc+0x12e/0x760 mm/slab.c:3561 >>> kmem_cache_zalloc include/linux/slab.h:656 [inline] >>> mmap_region+0x7ee/0x15a0 mm/mmap.c:1658 >>> do_mmap+0x69b/0xd40 mm/mmap.c:1468 >>> do_mmap_pgoff include/linux/mm.h:2150 [inline] >>> vm_mmap_pgoff+0x1de/0x280 mm/util.c:333 >>> SYSC_mmap_pgoff mm/mmap.c:1518 [inline] >>> SyS_mmap_pgoff+0x23b/0x5f0 mm/mmap.c:1476 >>> SYSC_mmap arch/x86/kernel/sys_x86_64.c:99 [inline] >>> SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:90 >>> entry_SYSCALL_64_fastpath+0x1f/0xbe >>> >>> Freed by task 8007: >>> save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 >>> save_stack+0x43/0xd0 mm/kasan/kasan.c:447 >>> set_track mm/kasan/kasan.c:459 [inline] >>> kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524 >>> __cache_free mm/slab.c:3503 [inline] >>> kmem_cache_free+0x77/0x280 mm/slab.c:3763 >>> remove_vma+0x162/0x1b0 mm/mmap.c:176 >>> remove_vma_list mm/mmap.c:2475 [inline] >>> do_munmap+0x82a/0xdf0 mm/mmap.c:2714 >>> mmap_region+0x59e/0x15a0 mm/mmap.c:1631 >>> do_mmap+0x69b/0xd40 mm/mmap.c:1468 >>> do_mmap_pgoff include/linux/mm.h:2150 [inline] >>> vm_mmap_pgoff+0x1de/0x280 mm/util.c:333 >>> SYSC_mmap_pgoff mm/mmap.c:1518 [inline] >>> SyS_mmap_pgoff+0x23b/0x5f0 mm/mmap.c:1476 >>> SYSC_mmap arch/x86/kernel/sys_x86_64.c:99 [inline] >>> SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:90 >>> entry_SYSCALL_64_fastpath+0x1f/0xbe >>> >>> The buggy address belongs to the object at ffff880064d19a50 >>> which belongs to the cache vm_area_struct of size 200 >>> The buggy address is located 80 bytes inside of >>> 200-byte region [ffff880064d19a50, ffff880064d19b18) >>> The buggy address belongs to the page: >>> page:ffffea0001934640 count:1 mapcount:0 mapping:ffff880064d19000 index:0x0 >>> flags: 0x100000000000100(slab) >>> raw: 0100000000000100 ffff880064d19000 0000000000000000 000000010000000f >>> raw: ffffea00018a3a60 ffffea0001940be0 ffff88006c5f79c0 0000000000000000 >>> page dumped because: kasan: bad access detected >>> >>> Memory state around the buggy address: >>> ffff880064d19980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>> ffff880064d19a00: fb fb fc fc fc fc fc fc fc fc fb fb fb fb fb fb >>>> ffff880064d19a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>> ^ >>> ffff880064d19b00: fb fb fb fc fc fc fc fc fc fc fc fb fb fb fb fb >>> ffff880064d19b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>> ================================================================== >>> >>> >>> Here is disasm of the function: >>> https://gist.githubusercontent.com/dvyukov/5a56c66ce605168c951a321d94df6e3a/raw/538d4ce72ceb5631dfcc866ccde46c74543de1cf/gistfile1.txt >>> >>> Seems to be vma->vm_flags at offset 80. >> >> You can see it from the disasm? I can't make much of it, unfortunately, >> the added kasan calls obscure it a lot for me. But I suspect it might be >> the vma_pkey() thing which reads from vma->vm_flags. What happens when >> CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS is disabled? (or is it already?) > > OK, so I opened the google groups link in the report's signature and > looked at the attached config there, which says protkeys are enabled. > Also looked at the repro.txt attachment: > #{Threaded:true Collide:true Repeat:true Procs:8 Sandbox:none Fault:false FaultCall:-1 FaultNth:0 EnableTun:true UseTmpDir:true HandleSegv:true WaitRepeat:true Debug:false Repro:false} > mmap(&(0x7f0000000000/0xfff000)=nil, 0xfff000, 0x3, 0x32, 0xffffffffffffffff, 0x0) > mmap(&(0x7f0000011000/0x3000)=nil, 0x3000, 0x1, 0x32, 0xffffffffffffffff, 0x0) > r0 = userfaultfd(0x0) > ioctl$UFFDIO_API(r0, 0xc018aa3f, &(0x7f0000002000-0x18)={0xaa, 0x0, 0x0}) > ioctl$UFFDIO_REGISTER(r0, 0xc020aa00, &(0x7f0000019000)={{&(0x7f0000012000/0x2000)=nil, 0x2000}, 0x1, 0x0}) > r1 = gettid() > syz_open_dev$evdev(&(0x7f0000013000-0x12)="2f6465762f696e7075742f6576656e742300", 0x0, 0x0) > tkill(r1, 0x7) > > The userfaultfd() caught my attention so I checked handle_userfault() > which seems to do up_read(&mm->mmap_sem); and in some cases later > followed by down_read(&mm->mmap_sem); return VM_FAULT_NOPAGE. > However, __do_page_fault() only expects that mmap_sem to be released > when handle_mm_fault() returns with VM_FAULT_RETRY. It doesn't expect it > to be released and then acquired again, because then vma can be indeed > gone. It seems vma hasn't been touched after that point until the > vma_pkey() was added by commit a3c4fb7c9c2e ("x86/mm: Fix fault error > path using unsafe vma pointer") in rc3. Which tried to fix a similar > problem, but run into this corner case? > > So I suspect a3c4fb7c9c2e is the culprit and thus a regression. Yes that's my mistake. My patch was removing the use of vma once mmap_sem is released but it was mainly done in the error path and I moved the read of the vma's pkey before releasing the mmap_sem, but in the no-error path also, leading to the use after free you seen. As suggested and done later in this thread, reading the vma's key value before calling handle_mm_fault() will solve this issue. This is safe since the vma's pkey can't be changed once the mmap_sem is held. Thanks, Laurent. > >> Also did you try the vmacache shortcut test suggested in my previous mail? >> >>> I think the size of 200 reported by slab is OK as it can do some rounding. >>> Everything points to a vma object. >>> >>> >>>>>> The buggy address belongs to the page: >>>>>> page:ffffea00072ff4c0 count:1 mapcount:0 mapping:ffff8801cbfd3040 index:0x0 >>>>>> flags: 0x200000000000100(slab) >>>>>> raw: 0200000000000100 ffff8801cbfd3040 0000000000000000 000000010000000f >>>>>> raw: ffffea000730c7a0 ffffea00072ff7a0 ffff8801dae069c0 0000000000000000 >>>>>> page dumped because: kasan: bad access detected >>>>>> >>>>>> Memory state around the buggy address: >>>>>> ffff8801cbfd2f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >>>>>> ffff8801cbfd3000: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb >>>>>>> >>>>>>> ffff8801cbfd3080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>>>>> >>>>>> ^ >>>>>> ffff8801cbfd3100: fb fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb >>>>>> ffff8801cbfd3180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >>>>>> ================================================================== >>>>> >>>>> >>>>> I guess this is more related to mm rather than x86, so +mm maintainers. >>>>> This continues to happen, in particular on upstream >>>>> 781402340475144bb360e32bb7437fa4b84cadc3 (Oct 28). >>>>> >>>>> >>>>>> --- >>>>>> This bug is generated by a dumb bot. It may contain errors. >>>>>> See https://goo.gl/tpsmEJ for details. >>>>>> Direct all questions to syzkaller@xxxxxxxxxxxxxxxx. >>>>>> >>>>>> syzbot will keep track of this bug report. >>>>>> Once a fix for this bug is committed, please reply to this email with: >>>>>> #syz fix: exact-commit-title >>>>>> To mark this as a duplicate of another syzbot report, please reply with: >>>>>> #syz dup: exact-subject-of-another-report >>>>>> If it's a one-off invalid bug report, please reply with: >>>>>> #syz invalid >>>>>> Note: if the crash happens again, it will cause creation of a new bug >>>>>> report. >>>>>> >>>>>> -- >>>>>> You received this message because you are subscribed to the Google Groups >>>>>> "syzkaller-bugs" group. >>>>>> To unsubscribe from this group and stop receiving emails from it, send an >>>>>> email to syzkaller-bugs+unsubscribe@xxxxxxxxxxxxxxxx. >>>>>> To view this discussion on the web visit >>>>>> https://groups.google.com/d/msgid/syzkaller-bugs/94eb2c0433c8f42cac055cc86991%40google.com. >>>>>> For more options, visit https://groups.google.com/d/optout. >>>>> >>>>> -- >>>>> To unsubscribe, send a message with 'unsubscribe linux-mm' in >>>>> the body to majordomo@xxxxxxxxx. For more info on Linux MM, >>>>> see: http://www.linux-mm.org/ . >>>>> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> >>>>> >>>> >> >> -- >> To unsubscribe, send a message with 'unsubscribe linux-mm' in >> the body to majordomo@xxxxxxxxx. For more info on Linux MM, >> see: http://www.linux-mm.org/ . >> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> >> > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
