Re: [syzbot] WARNING in nested_vmx_vmexit

Sean Christopherson
2021-12-06T16:45:18Z

On Mon, Dec 06, 2021, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@google.com> writes:
> > 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@google.com/

Boom. VCPU_RUN exits with KVM_EXIT_INTERNAL_ERROR.

diff --git a/tools/testing/selftests/kvm/x86_64/vmx_close_while_nested_test.c b/tools/testing/selftests/kvm/x86_64/vmx_close_while_nested_test.c
index 2835a17f1b7a..4f77c5d7c7b9 100644
--- a/tools/testing/selftests/kvm/x86_64/vmx_close_while_nested_test.c
+++ b/tools/testing/selftests/kvm/x86_64/vmx_close_while_nested_test.c
@@ -27,6 +27,11 @@ enum {
/* The virtual machine object. */
static struct kvm_vm *vm;

+static void l2_guest_infinite_loop(void)
+{
+ while (1);
+}
+
static void l2_guest_code(void)
{
/* Exit to L0 */
@@ -53,6 +58,9 @@ static void l1_guest_code(struct vmx_pages *vmx_pages)
int main(int argc, char *argv[])
{
vm_vaddr_t vmx_pages_gva;
+ struct kvm_sregs sregs;
+ struct kvm_regs regs;
+ int r;

nested_vmx_check_supported();

@@ -83,4 +91,17 @@ int main(int argc, char *argv[])
TEST_FAIL("Unknown ucall %lu", uc.cmd);
}
}
+
+ memset(&regs, 0, sizeof(regs));
+ vcpu_regs_get(vm, VCPU_ID, &regs);
+ regs.rip = (u64)l2_guest_infinite_loop;
+ vcpu_regs_set(vm, VCPU_ID, &regs);
+
+ memset(&sregs, 0, sizeof(sregs));
+ vcpu_sregs_get(vm, VCPU_ID, &sregs);
+ sregs.tr.unusable = 1;
+ vcpu_sregs_set(vm, VCPU_ID, &sregs);
+
+ r = _vcpu_run(vm, VCPU_ID);
+ TEST_ASSERT(0, "Unexpected return from L2, r = %d, exit_reason = %d", r, vcpu_state(vm, VCPU_ID)->exit_reason);
}

------------[ cut here ]------------
WARNING: CPU: 6 PID: 273926 at arch/x86/kvm/vmx/nested.c:4565 nested_vmx_vmexit+0xd59/0xdb0 [kvm_intel]
CPU: 6 PID: 273926 Comm: vmx_close_while Not tainted 5.15.2-7cc36c3e14ae-pop #279
Hardware name: ASUS Q87M-E/Q87M-E, BIOS 1102 03/03/2014
RIP: 0010:nested_vmx_vmexit+0xd59/0xdb0 [kvm_intel]
Call Trace:
vmx_leave_nested+0x30/0x40 [kvm_intel]
nested_vmx_free_vcpu+0x16/0x20 [kvm_intel]
vmx_free_vcpu+0x4b/0x60 [kvm_intel]
kvm_arch_vcpu_destroy+0x40/0x160 [kvm]
kvm_vcpu_destroy+0x1d/0x50 [kvm]
kvm_arch_destroy_vm+0xc1/0x1c0 [kvm]
kvm_put_kvm+0x187/0x2a0 [kvm]
kvm_vm_release+0x1d/0x30 [kvm]
__fput+0x95/0x250
task_work_run+0x5f/0x90
do_exit+0x3c8/0xab0
do_group_exit+0x47/0xb0
__x64_sys_exit_group+0x14/0x20
do_syscall_64+0x3b/0xc0
entry_SYSCALL_64_after_hwframe+0x44/0xae