Re: [PATCH 2/3] KVM: nVMX: additional checks on vmxon region

[Jan Kiszka]

On 2014-04-28 07:00, Bandan Das wrote:
> Currently, the vmxon region isn't used in the nested case.
> However, according to the spec, the vmxon instruction performs
> additional sanity checks on this region and the associated
> pointer. Modify emulated vmxon to better adhere to the spec
> requirements
> 
> Signed-off-by: Bandan Das <bsd@xxxxxxxxxx>
> ---
>  arch/x86/kvm/vmx.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 53 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index c18fe9a4..d5342c7 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -354,6 +354,7 @@ struct vmcs02_list {
>  struct nested_vmx {
>  	/* Has the level1 guest done vmxon? */
>  	bool vmxon;
> +	gpa_t vmxon_ptr;
>  
>  	/* The guest-physical address of the current VMCS L1 keeps for L2 */
>  	gpa_t current_vmptr;
> @@ -5840,9 +5841,19 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
>  	struct kvm_segment cs;
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
>  	struct vmcs *shadow_vmcs;
> +	gva_t gva;
> +	gpa_t vmptr;
> +	struct x86_exception e;
> +	struct page *page;
> +
>  	const u64 VMXON_NEEDED_FEATURES = FEATURE_CONTROL_LOCKED
>  		| FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX;
>  
> +	/* Guest physical Address Width */
> +	struct kvm_cpuid_entry2 *best =
> +		kvm_find_cpuid_entry(vcpu, 0x80000008, 0);

We have cpuid_maxphyaddr().

> +
> +
>  	/* The Intel VMX Instruction Reference lists a bunch of bits that
>  	 * are prerequisite to running VMXON, most notably cr4.VMXE must be
>  	 * set to 1 (see vmx_set_cr4() for when we allow the guest to set this).
> @@ -5865,6 +5876,46 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
>  		kvm_inject_gp(vcpu, 0);
>  		return 1;
>  	}
> +
> +	if (get_vmx_mem_address(vcpu, vmcs_readl(EXIT_QUALIFICATION),
> +				vmcs_read32(VMX_INSTRUCTION_INFO), &gva))
> +		return 1;
> +
> +	if (kvm_read_guest_virt(&vcpu->arch.emulate_ctxt, gva, &vmptr,
> +				sizeof(vmptr), &e)) {
> +		kvm_inject_page_fault(vcpu, &e);
> +		return 1;
> +	}
> +
> +	/* Don't bailout if best is NULL */
> +	WARN_ON(!best);
> +
> +	/*
> +	 * SDM 3: 24.11.5
> +	 * VMXON pointer must be 4KB aligned
> +	 * VMXON pointer must not set any bits beyond processor's
> +	 * physical address width
> +	 * The first 4 bytes of VMXON region contain the supported
> +	 * VMCS revision identifier
> +	 *
> +	 * Note - IA32_VMX_BASIC[48] will never be 1 for the nested case;
> +	 * which replaces physical address width with 32
> +	 */
> +	if (!IS_ALIGNED(vmptr, PAGE_SIZE) || (best &&
> +					      (vmptr >> (best->eax & 0xff)))) {
> +		nested_vmx_failInvalid(vcpu);
> +		skip_emulated_instruction(vcpu);
> +		return 1;
> +	}
> +
> +	page = nested_get_page(vcpu, vmptr);
> +	if ((page == NULL) || ((*(u32 *)kmap(page) != VMCS12_REVISION))) {

Style: you don't need braces around the comparisons.

> +		nested_vmx_failInvalid(vcpu);
> +		kunmap(page);
> +		skip_emulated_instruction(vcpu);
> +		return 1;
> +	}
> +
>  	if (vmx->nested.vmxon) {
>  		nested_vmx_failValid(vcpu, VMXERR_VMXON_IN_VMX_ROOT_OPERATION);
>  		skip_emulated_instruction(vcpu);
> @@ -5896,9 +5947,11 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
>  	vmx->nested.preemption_timer.function = vmx_preemption_timer_fn;
>  
>  	vmx->nested.vmxon = true;
> +	vmx->nested.vmxon_ptr = vmptr;
>  
>  	skip_emulated_instruction(vcpu);
>  	nested_vmx_succeed(vcpu);
> +	kunmap(page);

This late unmapping leaks the page in other error cases.

Jan

>  	return 1;
>  }
>  
> 

-- 
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
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