ACK: [trusty/master-next 1/1] UBUNTU: SAUCE: KVM has a flaw in INVEPT emulation that could crash the host

[Colin Ian King]

On 25/04/17 18:57, Andy Whitcroft wrote:
> [ 1046.384746] BUG: unable to handle kernel NULL pointer dereference at 0000000000000070
> [ 1046.387386] IP: [<ffffffffa05b3ca3>] handle_invept+0x123/0x170 [kvm_intel]
> [ 1046.389577] PGD 0
> [ 1046.390273] Oops: 0000 [#1] SMP
> 
> (tested with Ubuntu 14.04 linux-image-3.13.0-113-generic)
> 
> The host KVM touches NULL pointer (vmx->nested.current_vmcs12) when a
> (crafted or buggy) guest issues a single-context INVEPT instruction
> *without* VMPTRLD like this:
> 
> 	kvm_cpu_vmxon(phys_addr);
> 	ept_sync_context(0);
> 
> (requires nested EPT; full PoC module code attached)
> 
> This flaw was introduced in commit bfd0a56b90005f8c8a004baf407ad90045c2b11e
> (nEPT: Nested INVEPT) and removed in 4b855078601fc422dbac3059f2215e776f49780f
> (KVM: nVMX: Don't advertise single context invalidation for invept).
> 
> Original-Patch-By: Minoura Makoto <minoura at valinux.co.jp>
> CVE-2017-8106
> BugLink: http://bugs.launchpad.net/bugs/1678676
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=195167
> Reviewed-by: Tyler Hicks <tyhicks at canonical.com>
> Signed-off-by: Andy Whitcroft <apw at canonical.com>
> ---
>  arch/x86/kvm/vmx.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 6658c0bf3666..57eae7732493 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -6386,6 +6386,8 @@ static int handle_invept(struct kvm_vcpu *vcpu)
>  
>  	switch (type) {
>  	case VMX_EPT_EXTENT_CONTEXT:
> +		if (to_vmx(vcpu)->nested.current_vmptr == -1ull)
> +			break;
>  		if ((operand.eptp & eptp_mask) !=
>  				(nested_ept_get_cr3(vcpu) & eptp_mask))
>  			break;
> 

Has been tested, looks OK to me.

Acked-by: Colin Ian King <colin.king at canonical.com>