Re: kvm: WARNING in mmu_spte_clear_track_bits

[Paolo Bonzini]

On 13/01/2017 12:15, Dmitry Vyukov wrote:
> 
> I've commented out the WARNING for now, but I am seeing lots of
> use-after-free's and rcu stalls involving mmu_spte_clear_track_bits:
> 
> 
> BUG: KASAN: use-after-free in mmu_spte_clear_track_bits+0x186/0x190
> arch/x86/kvm/mmu.c:597 at addr ffff880068ae2008
> Read of size 8 by task syz-executor2/16715
> page:ffffea00016e6170 count:0 mapcount:0 mapping:          (null) index:0x0
> flags: 0x500000000000000()
> raw: 0500000000000000 0000000000000000 0000000000000000 00000000ffffffff
> raw: ffffea00017ec5a0 ffffea0001783d48 ffff88006aec5d98
> page dumped because: kasan: bad access detected
> CPU: 2 PID: 16715 Comm: syz-executor2 Not tainted 4.10.0-rc3+ #163
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:15 [inline]
>  dump_stack+0x292/0x3a2 lib/dump_stack.c:51
>  kasan_report_error mm/kasan/report.c:213 [inline]
>  kasan_report+0x42d/0x460 mm/kasan/report.c:307
>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:333
>  mmu_spte_clear_track_bits+0x186/0x190 arch/x86/kvm/mmu.c:597
>  drop_spte+0x24/0x280 arch/x86/kvm/mmu.c:1182
>  kvm_zap_rmapp+0x119/0x260 arch/x86/kvm/mmu.c:1401
>  kvm_unmap_rmapp+0x1d/0x30 arch/x86/kvm/mmu.c:1412
>  kvm_handle_hva_range+0x54a/0x7d0 arch/x86/kvm/mmu.c:1565
>  kvm_unmap_hva_range+0x2e/0x40 arch/x86/kvm/mmu.c:1591
>  kvm_mmu_notifier_invalidate_range_start+0xae/0x140
> arch/x86/kvm/../../../virt/kvm/kvm_main.c:360
>  __mmu_notifier_invalidate_range_start+0x1f8/0x300 mm/mmu_notifier.c:199
>  mmu_notifier_invalidate_range_start include/linux/mmu_notifier.h:282 [inline]
>  unmap_vmas+0x14b/0x1b0 mm/memory.c:1368
>  unmap_region+0x2f8/0x560 mm/mmap.c:2460
>  do_munmap+0x7b8/0xfa0 mm/mmap.c:2657
>  mmap_region+0x68f/0x18e0 mm/mmap.c:1612
>  do_mmap+0x6a2/0xd40 mm/mmap.c:1450
>  do_mmap_pgoff include/linux/mm.h:2031 [inline]
>  vm_mmap_pgoff+0x1a9/0x200 mm/util.c:305
>  SYSC_mmap_pgoff mm/mmap.c:1500 [inline]
>  SyS_mmap_pgoff+0x22c/0x5d0 mm/mmap.c:1458
>  SYSC_mmap arch/x86/kernel/sys_x86_64.c:95 [inline]
>  SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:86
>  entry_SYSCALL_64_fastpath+0x1f/0xc2
> RIP: 0033:0x445329
> RSP: 002b:00007fb33933cb58 EFLAGS: 00000282 ORIG_RAX: 0000000000000009
> RAX: ffffffffffffffda RBX: 0000000020000000 RCX: 0000000000445329
> RDX: 0000000000000003 RSI: 0000000000af1000 RDI: 0000000020000000
> RBP: 00000000006dfe90 R08: ffffffffffffffff R09: 0000000000000000
> R10: 0000000000000032 R11: 0000000000000282 R12: 0000000000700000
> R13: 0000000000000006 R14: ffffffffffffffff R15: 0000000020001000
> Memory state around the buggy address:
>  ffff880068ae1f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  ffff880068ae1f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> ffff880068ae2000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>                       ^
>  ffff880068ae2080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>  ffff880068ae2100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ==================================================================

This could be related to the gfn_to_rmap issues.

Paolo