On Tue, Mar 05, 2013 at 02:57:03PM +0200, Gleb Natapov wrote:
> On Mon, Mar 04, 2013 at 08:40:29PM +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>
> > ---
> >
> > Changes in v2:
> > - keep the non-misleading part of the comment in handle_set_cr0
> >
> > arch/x86/kvm/vmx.c | 46 +++++++++++++++++++++++++++++++---------------
> > 1 files changed, 31 insertions(+), 15 deletions(-)
> >
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index 7cc566b..832b7b4 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -4605,37 +4605,53 @@ 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)) {
> > + struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> > + unsigned long orig_val = val;
> > +
> > /*
> > * 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.
> > + * but did change L0 shadowed bits.
> > */
> > - if (kvm_set_cr0(vcpu, (val & vcpu->arch.cr0_guest_owned_bits) |
> > - (vcpu->arch.cr0 & ~vcpu->arch.cr0_guest_owned_bits)))
> > + 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;
> The more I look at it the more it looks correct to me. I will continue
> looking, but I think we can move VMXON_CR0_ALWAYSON check to
> vmx_set_cr0(). Same for cr4 case.
>
BTW would be nice to have unit test for nested :)
--
Gleb.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
