On Mon, 2021-12-06 at 17:16 +0100, Vitaly Kuznetsov wrote: > Sean Christopherson <seanjc@xxxxxxxxxx> writes: > > > On Mon, Dec 06, 2021, Vitaly Kuznetsov wrote: > > > syzbot <syzbot+f1d2136db9c80d4733e8@xxxxxxxxxxxxxxxxxxxxxxxxx> writes: > > > > > > > Hello, > > > > > > > > syzbot found the following issue on: > > > > > > > > HEAD commit: 5f58da2befa5 Merge tag 'drm-fixes-2021-12-03-1' of git://a.. > > > > git tree: upstream > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=14927309b00000 > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=e9ea28d2c3c2c389 > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=f1d2136db9c80d4733e8 > > > > compiler: Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.2 > > > > > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > > > Reported-by: syzbot+f1d2136db9c80d4733e8@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > > > ------------[ cut here ]------------ > > > > WARNING: CPU: 0 PID: 21158 at arch/x86/kvm/vmx/nested.c:4548 nested_vmx_vmexit+0x16bd/0x17e0 arch/x86/kvm/vmx/nested.c:4547 > > > > Modules linked in: > > > > CPU: 0 PID: 21158 Comm: syz-executor.1 Not tainted 5.16.0-rc3-syzkaller #0 > > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > > > RIP: 0010:nested_vmx_vmexit+0x16bd/0x17e0 arch/x86/kvm/vmx/nested.c:4547 > > > > > > The comment above this WARN_ON_ONCE() says: > > > > > > 4541) /* > > > 4542) * The only expected VM-instruction error is "VM entry with > > > 4543) * invalid control field(s)." Anything else indicates a > > > 4544) * problem with L0. And we should never get here with a > > > 4545) * VMFail of any type if early consistency checks are enabled. > > > 4546) */ > > > 4547) WARN_ON_ONCE(vmcs_read32(VM_INSTRUCTION_ERROR) != > > > 4548) VMXERR_ENTRY_INVALID_CONTROL_FIELD); > > > > > > which I think should still be valid and so the problem needs to be > > > looked at L0 (GCE infrastructure). Sean, Jim, your call :-) > > > > The assertion itself is still valid, but look at the call stack. This is firing > > when KVM tears down the VM, i.e. vmx->fail is likely stale. > > Oh, I see, true that! > > > I'll bet dollars to > > donuts that commit c8607e4a086f ("KVM: x86: nVMX: don't fail nested VM entry on > > invalid guest state if !from_vmentry") is to blame. L1 is running with > > unrestricted_guest=Y, so the only way vmx->emulation_required should become true > > is if L2 is active and is not an unrestricted guest. > > > > I objected to the patch[*], but looking back at the dates, it appears that I did > > so after the patch was queued and my comments were never addressed. > > I'll see if I can reproduce this with a selftest. The fix is likely just: > > > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > > index dc4909b67c5c..927a7c43b73b 100644 > > --- a/arch/x86/kvm/vmx/vmx.c > > +++ b/arch/x86/kvm/vmx/vmx.c > > @@ -6665,10 +6665,6 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu) > > * consistency check VM-Exit due to invalid guest state and bail. > > */ > > if (unlikely(vmx->emulation_required)) { > > - > > - /* We don't emulate invalid state of a nested guest */ > > - vmx->fail = is_guest_mode(vcpu); > > - > > vmx->exit_reason.full = EXIT_REASON_INVALID_STATE; > > vmx->exit_reason.failed_vmentry = 1; > > kvm_register_mark_available(vcpu, VCPU_EXREG_EXIT_INFO_1); > > > > [*] https://lore.kernel.org/all/YWDWPbgJik5spT1D@xxxxxxxxxx/ > > > > Let's also summon Max to the discussion to get his thoughts. I'll take a look at that soon. Need to page in the reason why this has to be done. I remember that we have wierd case of L1 beeing in invalid state, because some of the SMM's invalid state is leaking to L1 after a migration, and otherwise L1 while nested has to be in valid state: L1 really can't be in invalid state while in VMXON (even if it could theoretically, no way it can reach that point - I need to refresh my VMX knowelege to be sure about it), and L2 has to have valid state since that is the defintion of VMX - if L2 were in invalid state, then L1 would have to emualte L2 and not use VMX. I'll take a more detailed look soon at this. Best regards, Maxim Levitsky > > > > > <TASK> > > > > vmx_leave_nested arch/x86/kvm/vmx/nested.c:6220 [inline] > > > > nested_vmx_free_vcpu+0x83/0xc0 arch/x86/kvm/vmx/nested.c:330 > > > > vmx_free_vcpu+0x11f/0x2a0 arch/x86/kvm/vmx/vmx.c:6799 > > > > kvm_arch_vcpu_destroy+0x6b/0x240 arch/x86/kvm/x86.c:10989 > > > > kvm_vcpu_destroy+0x29/0x90 arch/x86/kvm/../../../virt/kvm/kvm_main.c:441 > > > > kvm_free_vcpus arch/x86/kvm/x86.c:11426 [inline] > > > > kvm_arch_destroy_vm+0x3ef/0x6b0 arch/x86/kvm/x86.c:11545 > > > > kvm_destroy_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:1189 [inline] > > > > kvm_put_kvm+0x751/0xe40 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1220 > > > > kvm_vcpu_release+0x53/0x60 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3489 > > > > __fput+0x3fc/0x870 fs/file_table.c:280 > > > > task_work_run+0x146/0x1c0 kernel/task_work.c:164 > > > > exit_task_work include/linux/task_work.h:32 [inline] > > > > do_exit+0x705/0x24f0 kernel/exit.c:832 > > > > do_group_exit+0x168/0x2d0 kernel/exit.c:929 > > > > get_signal+0x1740/0x2120 kernel/signal.c:2852 > > > > arch_do_signal_or_restart+0x9c/0x730 arch/x86/kernel/signal.c:868 > > > > handle_signal_work kernel/entry/common.c:148 [inline] > > > > exit_to_user_mode_loop kernel/entry/common.c:172 [inline] > > > > exit_to_user_mode_prepare+0x191/0x220 kernel/entry/common.c:207 > > > > __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline] > > > > syscall_exit_to_user_mode+0x2e/0x70 kernel/entry/common.c:300 > > > > do_syscall_64+0x53/0xd0 arch/x86/entry/common.c:86 > > > > entry_SYSCALL_64_after_hwframe+0x44/0xae > > > > RIP: 0033:0x7f3388806b19 > > > > Code: Unable to access opcode bytes at RIP 0x7f3388806aef. > > > > RSP: 002b:00007f338773a218 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca > > > > RAX: fffffffffffffe00 RBX: 00007f338891a0e8 RCX: 00007f3388806b19 > > > > RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f338891a0e8 > > > > RBP: 00007f338891a0e0 R08: 0000000000000000 R09: 0000000000000000 > > > > R10: 0000000000000000 R11: 0000000000000246 R12: 00007f338891a0ec > > > > R13: 00007fffbe0e838f R14: 00007f338773a300 R15: 0000000000022000 > > > > </TASK>
