On Thu, Feb 28, 2013 at 10:44:47AM +0100, Jan Kiszka wrote:
> The logic for calculating the value with which we call kvm_set_cr0/4 was
> broken (will definitely be visible with nested unrestricted guest mode
> support). Also, we performed the check regarding CR0_ALWAYSON too early
> when in guest mode.
>
> What really needs to be done on both CR0 and CR4 is to mask out L1-owned
> bits and merge them in from GUEST_CR0/4. In contrast, arch.cr0/4 and
> arch.cr0/4_guest_owned_bits contain the mangled L0+L1 state and, thus,
> are not suited as input.
>
> For both CRs, we can then apply the check against VMXON_CRx_ALWAYSON and
> refuse the update if it fails. To be fully consistent, we implement this
> check now also for CR4.
>
> Finally, we have to set the shadow to the value L2 wanted to write
> originally.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
> ---
>
> Found while making unrestricted guest mode working. Not sure what impact
> the bugs had on current feature level, if any.
>
> For interested folks, I've pushed my nEPT environment here:
>
> git://git.kiszka.org/linux-kvm.git nept-hacking
>
> arch/x86/kvm/vmx.c | 49 ++++++++++++++++++++++++++++++-------------------
> 1 files changed, 30 insertions(+), 19 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 7cc566b..d1dac08 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -4605,37 +4605,48 @@ vmx_patch_hypercall(struct kvm_vcpu *vcpu, unsigned char *hypercall)
> /* called to set cr0 as appropriate for a mov-to-cr0 exit. */
> static int handle_set_cr0(struct kvm_vcpu *vcpu, unsigned long val)
> {
> - if (to_vmx(vcpu)->nested.vmxon &&
> - ((val & VMXON_CR0_ALWAYSON) != VMXON_CR0_ALWAYSON))
> - return 1;
> -
> if (is_guest_mode(vcpu)) {
> - /*
> - * We get here when L2 changed cr0 in a way that did not change
> - * any of L1's shadowed bits (see nested_vmx_exit_handled_cr),
> - * but did change L0 shadowed bits. This can currently happen
> - * with the TS bit: L0 may want to leave TS on (for lazy fpu
> - * loading) while pretending to allow the guest to change it.
> - */
Can't say I understand this patch yet, but it looks like the comment is
still valid. Why have you removed it?
> - if (kvm_set_cr0(vcpu, (val & vcpu->arch.cr0_guest_owned_bits) |
> - (vcpu->arch.cr0 & ~vcpu->arch.cr0_guest_owned_bits)))
> + struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> + unsigned long orig_val = val;
> +
> + val = (val & ~vmcs12->cr0_guest_host_mask) |
> + (vmcs_read64(GUEST_CR0) & vmcs12->cr0_guest_host_mask);
> + if ((val & VMXON_CR0_ALWAYSON) != VMXON_CR0_ALWAYSON)
> + return 1;
> +
> + if (kvm_set_cr0(vcpu, val))
> return 1;
> - vmcs_writel(CR0_READ_SHADOW, val);
> + vmcs_writel(CR0_READ_SHADOW, orig_val);
> return 0;
> - } else
> + } else {
> + if (to_vmx(vcpu)->nested.vmxon &&
> + ((val & VMXON_CR0_ALWAYSON) != VMXON_CR0_ALWAYSON))
> + return 1;
> return kvm_set_cr0(vcpu, val);
> + }
> }
>
> static int handle_set_cr4(struct kvm_vcpu *vcpu, unsigned long val)
> {
> if (is_guest_mode(vcpu)) {
> - if (kvm_set_cr4(vcpu, (val & vcpu->arch.cr4_guest_owned_bits) |
> - (vcpu->arch.cr4 & ~vcpu->arch.cr4_guest_owned_bits)))
> + struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> + unsigned long orig_val = val;
> +
> + val = (val & ~vmcs12->cr4_guest_host_mask) |
> + (vmcs_readl(GUEST_CR4) & vmcs12->cr4_guest_host_mask);
> + if ((val & VMXON_CR4_ALWAYSON) != VMXON_CR4_ALWAYSON)
> + return 1;
> +
> + if (kvm_set_cr4(vcpu, val))
> return 1;
> - vmcs_writel(CR4_READ_SHADOW, val);
> + vmcs_writel(CR4_READ_SHADOW, orig_val);
> return 0;
> - } else
> + } else {
> + if (to_vmx(vcpu)->nested.vmxon &&
> + ((val & VMXON_CR4_ALWAYSON) != VMXON_CR4_ALWAYSON))
> + return 1;
> return kvm_set_cr4(vcpu, val);
> + }
> }
>
> /* called to set cr0 as approriate for clts instruction exit. */
> --
> 1.7.3.4
--
Gleb.
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