linux-kernel - Re: [PATCH v2] KVM: nVMX: reset nested_run_pending if the vCPU is going to be reset

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Date:   Mon, 6 Mar 2017 11:40:10 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v2] KVM: nVMX: reset nested_run_pending if the vCPU is
 going to be reset

Am 05.03.2017 um 23:17 schrieb Wanpeng Li:
> 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@...gle.com>
> Suggested-by: Radim Krčmář <rkrcmar@...hat.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.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);

Maybe move that directly into vmx_leave_nested()?

> +		}
>  		break;
>  	case MSR_IA32_VMX_BASIC ... MSR_IA32_VMX_VMFUNC:
>  		if (!msr_info->host_initiated)
> 


-- 
Thanks,

David