Re: general protection fault in vcpu_enter_guest (2)

[Sean Christopherson <sean.j.christopherson@intel.com>]

On Thu, Apr 25, 2019 at 05:07:05PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    76c938fc Add linux-next specific files for 20190423
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=16863d28a00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=62738d35457c577d
> dashboard link: https://syzkaller.appspot.com/bug?extid=f7e65445a40d3e0e4ebf
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1364a6d4a00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17c25dc4a00000
> 
> Bisection is inconclusive: the first bad commit could be any of:
> 
> 57bf67e7 KVM: lapic: Disable timer advancement if adaptive tuning goes
> haywire
> 39497d76 KVM: lapic: Track lapic timer advance per vCPU

Well that was depressingly easy to reproduce.  The per-vCPU commit is at
fault, it fails to ensure the lapic is in kernel before dereferencing the
associated pointer.  Patch incoming...

> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17a32fc4a00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+f7e65445a40d3e0e4ebf@syzkaller.appspotmail.com
> 
> L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and
> https://www.kernel.org/doc/html/latest/admin-guide/l1tf.html for details.
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 7872 Comm: syz-executor233 Not tainted 5.1.0-rc6-next-20190423
> #29
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:vcpu_enter_guest+0xbcd/0x5fb0 arch/x86/kvm/x86.c:7895
> Code: 48 c1 ea 03 80 3c 02 00 0f 85 6f 48 00 00 49 8b 9f b0 03 00 00 48 b8
> 00 00 00 00 00 fc ff df 48 8d 7b 78 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0
> 74 08 3c 03 0f 8e 39 48 00 00 8b 5b 78 31 ff 89
> RSP: 0018:ffff88808bd4fa00 EFLAGS: 00010006
> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff810d1ec9
> RDX: 000000000000000f RSI: ffffffff810ceef2 RDI: 0000000000000078
> RBP: ffff88808bd4fb10 R08: ffff8880a912e580 R09: ffffed1015d05dd0
> R10: ffffed1015d05dcf R11: ffff8880ae82ee7b R12: ffff88808f3e006c
> R13: 0000000000000001 R14: ffff88808f3e0070 R15: ffff88808f3e0040
> FS:  00007f7adb927700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fa0427eb000 CR3: 00000000939e4000 CR4: 00000000001426f0
> Call Trace:
>  vcpu_run arch/x86/kvm/x86.c:8037 [inline]
>  kvm_arch_vcpu_ioctl_run+0x425/0x1750 arch/x86/kvm/x86.c:8245
>  kvm_vcpu_ioctl+0x4dc/0xf90 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2684
>  vfs_ioctl fs/ioctl.c:46 [inline]
>  file_ioctl fs/ioctl.c:509 [inline]
>  do_vfs_ioctl+0xd6e/0x1390 fs/ioctl.c:696
>  ksys_ioctl+0xab/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+0x103/0x670 arch/x86/entry/common.c:298
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x446779
> Code: e8 5c b3 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 0b 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f7adb926db8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00000000006dbc48 RCX: 0000000000446779
> RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000005
> RBP: 00000000006dbc40 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc4c
> R13: 00007fff1cfa7c1f R14: 00007f7adb9279c0 R15: 20c49ba5e353f7cf
> Modules linked in:
> ---[ end trace da6276bd16a5f99d ]---
> RIP: 0010:vcpu_enter_guest+0xbcd/0x5fb0 arch/x86/kvm/x86.c:7895
> Code: 48 c1 ea 03 80 3c 02 00 0f 85 6f 48 00 00 49 8b 9f b0 03 00 00 48 b8
> 00 00 00 00 00 fc ff df 48 8d 7b 78 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0
> 74 08 3c 03 0f 8e 39 48 00 00 8b 5b 78 31 ff 89
> RSP: 0018:ffff88808bd4fa00 EFLAGS: 00010006
> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff810d1ec9
> RDX: 000000000000000f RSI: ffffffff810ceef2 RDI: 0000000000000078
> RBP: ffff88808bd4fb10 R08: ffff8880a912e580 R09: ffffed1015d05dd0
> R10: ffffed1015d05dcf R11: ffff8880ae82ee7b R12: ffff88808f3e006c
> R13: 0000000000000001 R14: ffff88808f3e0070 R15: ffff88808f3e0040
> FS:  00007f7adb927700(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fa0427eb000 CR3: 00000000939e4000 CR4: 00000000001426f0
> 
> 
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
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> 
> syzbot will keep track of this bug report. See:
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> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches