Date:   Tue, 27 Nov 2018 13:07:30 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     syzbot+ff40b9bc4835ea83211c@...kaller.appspotmail.com,
        kvm <kvm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KASAN: use-after-free Read in kvm_write_guest_offset_cached

On Tue, Nov 27, 2018 at 7:14 AM, Wanpeng Li <kernellwp@...il.com> wrote:
>
> On Tue, 27 Nov 2018 at 12:51, syzbot
> <syzbot+ff40b9bc4835ea83211c@...kaller.appspotmail.com> wrote:
> >
> > Hello,
>
> Is there beauty C codes?

syzbot does not have code like:

if (rand() % 2)
  send_C_repro();

:)

> > syzbot found the following crash on:
> >
> > HEAD commit:    442b8cea2477 Add linux-next specific files for 20181109
> > git tree:       linux-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=174d326d400000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=2f72bdb11df9fbe8
> > dashboard link: https://syzkaller.appspot.com/bug?extid=ff40b9bc4835ea83211c
> > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14f5df7b400000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+ff40b9bc4835ea83211c@...kaller.appspotmail.com
> >
> > ==================================================================
> > BUG: KASAN: use-after-free in mark_page_dirty_in_slot
> > arch/x86/kvm/../../../virt/kvm/kvm_main.c:2056 [inline]
> > BUG: KASAN: use-after-free in kvm_write_guest_offset_cached+0x693/0x6b0
> > arch/x86/kvm/../../../virt/kvm/kvm_main.c:1988
> > Read of size 8 at addr ffff8801b9363778 by task syz-executor1/30438
> >
> > CPU: 1 PID: 30438 Comm: syz-executor1 Not tainted 4.20.0-rc1-next-20181109+
> > #110
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > Call Trace:
> >   __dump_stack lib/dump_stack.c:77 [inline]
> >   dump_stack+0x244/0x39d lib/dump_stack.c:113
> >   print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
> >   kasan_report_error mm/kasan/report.c:354 [inline]
> >   kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
> >   __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
> >   mark_page_dirty_in_slot arch/x86/kvm/../../../virt/kvm/kvm_main.c:2056
> > [inline]
> >   kvm_write_guest_offset_cached+0x693/0x6b0
> > arch/x86/kvm/../../../virt/kvm/kvm_main.c:1988
> >   kvm_steal_time_set_preempted arch/x86/kvm/x86.c:3241 [inline]
> >   kvm_arch_vcpu_put+0x365/0x420 arch/x86/kvm/x86.c:3268
> >   kvm_sched_out+0x91/0xb0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3993
> >   __fire_sched_out_preempt_notifiers kernel/sched/core.c:2503 [inline]
> >   fire_sched_out_preempt_notifiers kernel/sched/core.c:2511 [inline]
> >   prepare_task_switch kernel/sched/core.c:2617 [inline]
> >   context_switch kernel/sched/core.c:2796 [inline]
> >   __schedule+0x11ca/0x21d0 kernel/sched/core.c:3472
> >   preempt_schedule_irq+0xb9/0x140 kernel/sched/core.c:3699
> >   retint_kernel+0x1b/0x2d
> > RIP: 0010:search_memslots include/linux/kvm_host.h:955 [inline]
> > RIP: 0010:__gfn_to_memslot include/linux/kvm_host.h:976 [inline]
> > RIP: 0010:__kvm_gfn_to_hva_cache_init+0x2ed/0xd10
> > arch/x86/kvm/../../../virt/kvm/kvm_main.c:1935
> > Code: 3c 02 00 0f 85 0d 0a 00 00 4d 03 6c 24 08 48 89 df 4c 89 ee e8 04 16
> > 78 00 4c 39 eb 0f 82 6e 01 00 00 45 31 ed e8 43 15 78 00 <44> 89 fe 44 89
> > ef e8 c8 15 78 00 45 39 fd 0f 8d cf 00 00 00 e8 2a
> > RSP: 0018:ffff8801cbfee970 EFLAGS: 00000293 ORIG_RAX: ffffffffffffff13
> > RAX: ffff8801b9a4c280 RBX: 0000000000000000 RCX: ffffffff8107942f
> > RDX: 0000000000000000 RSI: ffffffff8107936d RDI: 0000000000000006
> > RBP: ffff8801cbfeeb60 R08: ffff8801b9a4c280 R09: ffffed00342bb209
> > R10: ffffed00342bb209 R11: ffff8801a15d904b R12: 0000000000000017
> > R13: 0000000000000017 R14: 0000000000000016 R15: 0000000000000017
> >   kvm_gfn_to_hva_cache_init+0x15a/0x340
> > arch/x86/kvm/../../../virt/kvm/kvm_main.c:1963
> >   kvm_set_msr_common+0x1a0c/0x2670 arch/x86/kvm/x86.c:2549
> >   vmx_set_msr+0x759/0x1f90 arch/x86/kvm/vmx.c:4360
> >   kvm_set_msr+0x18a/0x370 arch/x86/kvm/x86.c:1324
> >   do_set_msr+0x10d/0x1a0 arch/x86/kvm/x86.c:1353
> >   __msr_io arch/x86/kvm/x86.c:2905 [inline]
> >   msr_io+0x222/0x380 arch/x86/kvm/x86.c:2941
> >   kvm_arch_vcpu_ioctl+0x961/0x3b00 arch/x86/kvm/x86.c:3956
> >   kvm_vcpu_ioctl+0x278/0x1150 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2748
> >   vfs_ioctl fs/ioctl.c:46 [inline]
> >   file_ioctl fs/ioctl.c:509 [inline]
> >   do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
> >   ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
> >   __do_sys_ioctl fs/ioctl.c:720 [inline]
> >   __se_sys_ioctl fs/ioctl.c:718 [inline]
> >   __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
> >   do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
> >   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > RIP: 0033:0x457569
> > Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
> > 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
> > ff 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> > RSP: 002b:00007fc292e62c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457569
> > RDX: 0000000020000280 RSI: 000000004008ae89 RDI: 0000000000000005
> > RBP: 000000000072c040 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 00007fc292e636d4
> > R13: 00000000004bff9d R14: 00000000004d0970 R15: 00000000ffffffff
> >
> > Allocated by task 30427:
> >   save_stack+0x43/0xd0 mm/kasan/kasan.c:448
> >   set_track mm/kasan/kasan.c:460 [inline]
> >   kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
> >   __do_kmalloc_node mm/slab.c:3684 [inline]
> >   __kmalloc_node+0x50/0x70 mm/slab.c:3691
> >   kmalloc_node include/linux/slab.h:589 [inline]
> >   kvmalloc_node+0xb9/0xf0 mm/util.c:416
> >   kvmalloc include/linux/mm.h:577 [inline]
> >   kvzalloc include/linux/mm.h:585 [inline]
> >   __kvm_set_memory_region+0x116e/0x2d50
> > arch/x86/kvm/../../../virt/kvm/kvm_main.c:1023
> >   kvm_set_memory_region+0x2e/0x50
> > arch/x86/kvm/../../../virt/kvm/kvm_main.c:1085
> >   kvm_vm_ioctl_set_memory_region
> > arch/x86/kvm/../../../virt/kvm/kvm_main.c:1097 [inline]
> >   kvm_vm_ioctl+0x652/0x1d60 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2995
> >   vfs_ioctl fs/ioctl.c:46 [inline]
> >   file_ioctl fs/ioctl.c:509 [inline]
> >   do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
> >   ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
> >   __do_sys_ioctl fs/ioctl.c:720 [inline]
> >   __se_sys_ioctl fs/ioctl.c:718 [inline]
> >   __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
> >   do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
> >   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > Freed by task 30427:
> >   save_stack+0x43/0xd0 mm/kasan/kasan.c:448
> >   set_track mm/kasan/kasan.c:460 [inline]
> >   __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
> >   kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
> >   __cache_free mm/slab.c:3498 [inline]
> >   kfree+0xcf/0x230 mm/slab.c:3817
> >   kvfree+0x61/0x70 mm/util.c:445
> >   __kvm_set_memory_region+0x1cb3/0x2d50
> > arch/x86/kvm/../../../virt/kvm/kvm_main.c:1067
> >   kvm_set_memory_region+0x2e/0x50
> > arch/x86/kvm/../../../virt/kvm/kvm_main.c:1085
> >   kvm_vm_ioctl_set_memory_region
> > arch/x86/kvm/../../../virt/kvm/kvm_main.c:1097 [inline]
> >   kvm_vm_ioctl+0x652/0x1d60 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2995
> >   vfs_ioctl fs/ioctl.c:46 [inline]
> >   file_ioctl fs/ioctl.c:509 [inline]
> >   do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
> >   ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
> >   __do_sys_ioctl fs/ioctl.c:720 [inline]
> >   __se_sys_ioctl fs/ioctl.c:718 [inline]
> >   __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
> >   do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
> >   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > The buggy address belongs to the object at ffff8801b9363080
> >   which belongs to the cache kmalloc-64k of size 65536
> > The buggy address is located 1784 bytes inside of
> >   65536-byte region [ffff8801b9363080, ffff8801b9373080)
> > The buggy address belongs to the page:
> > page:ffffea0006e4d800 count:1 mapcount:0 mapping:ffff8801da802500 index:0x0
> > compound_mapcount: 0
> > flags: 0x2fffc0000010200(slab|head)
> > raw: 02fffc0000010200 ffffea0006906808 ffffea0007034808 ffff8801da802500
> > raw: 0000000000000000 ffff8801b9363080 0000000100000001 0000000000000000
> > page dumped because: kasan: bad access detected
> >
> > Memory state around the buggy address:
> >   ffff8801b9363600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >   ffff8801b9363680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > > ffff8801b9363700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >                                                                  ^
> >   ffff8801b9363780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >   ffff8801b9363800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ==================================================================
> >
> >
> > ---
> > This bug is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@...glegroups.com.
> >
> > syzbot will keep track of this bug report. See:
> > https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> > syzbot.
> > syzbot can test patches for this bug, for details see:
> > https://goo.gl/tpsmEJ#testing-patches
>
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