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Subject[PATCH v2] KVM: nVMX: reset nested_run_pending if the vCPU is going to be reset
Date
Reported by syzkaller:

WARNING: CPU: 1 PID: 27742 at arch/x86/kvm/vmx.c:11029
nested_vmx_vmexit+0x5c35/0x74d0 arch/x86/kvm/vmx.c:11029
CPU: 1 PID: 27742 Comm: a.out Not tainted 4.10.0+ #229
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:15 [inline]
dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
panic+0x1fb/0x412 kernel/panic.c:179
__warn+0x1c4/0x1e0 kernel/panic.c:540
warn_slowpath_null+0x2c/0x40 kernel/panic.c:583
nested_vmx_vmexit+0x5c35/0x74d0 arch/x86/kvm/vmx.c:11029
vmx_leave_nested arch/x86/kvm/vmx.c:11136 [inline]
vmx_set_msr+0x1565/0x1910 arch/x86/kvm/vmx.c:3324
kvm_set_msr+0xd4/0x170 arch/x86/kvm/x86.c:1099
do_set_msr+0x11e/0x190 arch/x86/kvm/x86.c:1128
__msr_io arch/x86/kvm/x86.c:2577 [inline]
msr_io+0x24b/0x450 arch/x86/kvm/x86.c:2614
kvm_arch_vcpu_ioctl+0x35b/0x46a0 arch/x86/kvm/x86.c:3497
kvm_vcpu_ioctl+0x232/0x1120 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2721
vfs_ioctl fs/ioctl.c:43 [inline]
do_vfs_ioctl+0x1bf/0x1790 fs/ioctl.c:683
SYSC_ioctl fs/ioctl.c:698 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:689
entry_SYSCALL_64_fastpath+0x1f/0xc2

The syzkaller folks reported a nested_run_pending warning during userspace clear VMX
capability which is exposed to L1 before.

The warning gets thrown while doing

(*(uint32_t*)0x20aecfe8 = (uint32_t)0x1);
(*(uint32_t*)0x20aecfec = (uint32_t)0x0);
(*(uint32_t*)0x20aecff0 = (uint32_t)0x3a);
(*(uint32_t*)0x20aecff4 = (uint32_t)0x0);
(*(uint64_t*)0x20aecff8 = (uint64_t)0x0);
r[29] = syscall(__NR_ioctl, r[4], 0x4008ae89ul,
0x20aecfe8ul, 0, 0, 0, 0, 0, 0);

i.e. KVM_SET_MSR ioctl with

struct kvm_msrs {
.nmsrs = 1,
.pad = 0,
.entries = {
{.index = MSR_IA32_FEATURE_CONTROL,
.reserved = 0,
.data = 0}
}
}

The VMLANCH/VMRESUME emulation should be stopped since the CPU is going to reset here.
This patch resets the nested_run_pending since the CPU is going to be reset hence there
should be nothing pending.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Suggested-by: Radim Krčmář <rkrcmar@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
v1 -> v2:
* cleanup comments format

arch/x86/kvm/vmx.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 283aa86..b4a757369 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3310,8 +3310,10 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
FEATURE_CONTROL_LOCKED && !msr_info->host_initiated))
return 1;
vmx->msr_ia32_feature_control = data;
- if (msr_info->host_initiated && data == 0)
+ if (msr_info->host_initiated && data == 0) {
+ vmx->nested.nested_run_pending = 0;
vmx_leave_nested(vcpu);
+ }
break;
case MSR_IA32_VMX_BASIC ... MSR_IA32_VMX_VMFUNC:
if (!msr_info->host_initiated)
--
2.7.4
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