kvm: WARNING in em_jmp_far

[Dmitry Vyukov]

Hello,

The following program triggers WARNING in em_jmp_far:
https://gist.githubusercontent.com/dvyukov/16bfd3d68fa7d5461101ef74e07796e4/raw/e6d663980681f2c5838ff6cd361cede7d3204838/gistfile1.txt


WARNING: CPU: 1 PID: 15748 at arch/x86/kvm/emulate.c:2128 em_jmp_far+0x4a7/0x530
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 15748 Comm: syz-executor Not tainted 4.9.0-rc5+ #28
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
 ffff880033986ec8 ffffffff834c2959 ffffffff00000001 1ffff10006730d6c
 ffffed0006730d64 0000000041b58ab3 ffffffff89575430 ffffffff834c266b
 0000000041b58ab3 ffffffff894d1810 ffffffff8158f020 ffffffff811ac787
Call Trace:
 [<     inline     >] __dump_stack lib/dump_stack.c:15
 [<ffffffff834c2959>] dump_stack+0x2ee/0x3f5 lib/dump_stack.c:51
 [<ffffffff81848908>] panic+0x200/0x425 kernel/panic.c:179
 [<ffffffff813fc919>] __warn+0x1c9/0x1e0 kernel/panic.c:542
 [<ffffffff813fcb81>] warn_slowpath_null+0x31/0x40 kernel/panic.c:585
 [<ffffffff81157867>] em_jmp_far+0x4a7/0x530 arch/x86/kvm/emulate.c:2128
 [<ffffffff811614ef>] x86_emulate_insn+0x43f/0x4090 arch/x86/kvm/emulate.c:5294
 [<ffffffff810e121e>] x86_emulate_instruction+0x43e/0x2300
arch/x86/kvm/x86.c:5547
 [<     inline     >] emulate_instruction arch/x86/include/asm/kvm_host.h:1116
 [<     inline     >] complete_emulated_io arch/x86/kvm/x86.c:6872
 [<ffffffff810e384e>] complete_emulated_mmio+0x76e/0xb70 arch/x86/kvm/x86.c:6936
 [<ffffffff810f1c92>] kvm_arch_vcpu_ioctl_run+0x3562/0x4eb0
arch/x86/kvm/x86.c:6980
 [<ffffffff8107b328>] kvm_vcpu_ioctl+0x678/0x11c0
arch/x86/kvm/../../../virt/kvm/kvm_main.c:2557
 [<     inline     >] vfs_ioctl fs/ioctl.c:43
 [<ffffffff81abcb44>] do_vfs_ioctl+0x1c4/0x1630 fs/ioctl.c:679
 [<     inline     >] SYSC_ioctl fs/ioctl.c:694
 [<ffffffff81abe044>] SyS_ioctl+0x94/0xc0 fs/ioctl.c:685
 [<ffffffff88143885>] entry_SYSCALL_64_fastpath+0x23/0xc6
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
reboot: cpu_has_vmx: ecx=80a02021 1

On commit a25f0944ba9b1d8a6813fd6f1a86f1bd59ac25a6 (Nov 13).