kvm: GPF in __get_kvmclock_ns

[Dmitry Vyukov]

Hello,

The following program triggers GPF in __get_kvmclock_ns if run in a loop:
https://gist.githubusercontent.com/dvyukov/91e4b366019e8500bac73ead5fbc44b0/raw/18178c254775dc953c4b5cf75442207480d939b4/gistfile1.txt

On commit 015ed9433be2b476ec7e2e6a9a411a56e3b5b035 (Nov 11).

general protection fault: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 3 PID: 4898 Comm: syz-executor Not tainted 4.9.0-rc4+ #40
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
task: ffff880066e32dc0 task.stack: ffff880067280000
RIP: 0010:[<ffffffff8108d3be>]  [<ffffffff8108d3be>]
__get_kvmclock_ns+0x5e/0x390 arch/x86/kvm/x86.c:1731
RSP: 0018:ffff8800672878c0  EFLAGS: 00010003
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffc90000766000
RDX: 000000000000064c RSI: 0000000000000000 RDI: 0000000000003265
RBP: ffff8800672878f0 R08: ffffed000ce50f3e R09: ffffed000ce50f3e
R10: ffffed000ce50f3d R11: ffff8800672879ef R12: ffff88006728c000
R13: ffff88006728c000 R14: 000000002000d000 R15: ffffffffffffffea
FS:  00007f0b2288a700(0000) GS:ffff88006e300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000002000d000 CR3: 00000000672ba000 CR4: 00000000000026e0
Stack:
 0000000000000046 1ffff1000ce50f24 1ffff1000ce50f24 ffff8800672879c0
 ffff88006728c000 000000002000d000 ffff880067287b90 ffffffff810aafd8
 0000000000000038 ffff880067287948 ffffffff812c10f5 1ffff1000ce50f2d
Call Trace:
 [<ffffffff810aafd8>] kvm_arch_vm_ioctl+0x1098/0x1c10 arch/x86/kvm/x86.c:4096
 [<ffffffff81065643>] kvm_vm_ioctl+0x193/0x1670
arch/x86/kvm/../../../virt/kvm/kvm_main.c:3097
 [<     inline     >] vfs_ioctl fs/ioctl.c:43
 [<ffffffff816b16fc>] do_vfs_ioctl+0x18c/0x1040 fs/ioctl.c:679
 [<     inline     >] SYSC_ioctl fs/ioctl.c:694
 [<ffffffff816b263f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff831ebd01>] entry_SYSCALL_64_fastpath+0x1f/0xc2
Code: 03 80 3c 02 00 0f 85 26 03 00 00 49 8b 9c 24 a0 03 00 00 48 b8
00 00 00 00 00 fc ff df 48 8d bb 65 32 00 00 48 89 fa 48 c1 ea 03 <0f>
b6 04 02 48 89 fa 83 e2 07 38 d0 7f 08 84 c0 0f 85 99 02 00
RIP  [<ffffffff8108d3be>] __get_kvmclock_ns+0x5e/0x390 arch/x86/kvm/x86.c:1731
 RSP <ffff8800672878c0>
---[ end trace 86f1ebae02f87a96 ]---
Kernel panic - not syncing: Fatal exception
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
reboot: cpu_has_vmx: ecx=80a02021 1


The line is:
    if (vcpu && vcpu->arch.hv_clock.flags & PVCLOCK_TSC_STABLE_BIT) {


Thanks