2015-11-02 21:22:22

by Radim Krčmář

Subject: [PATCH] KVM: VMX: fix SMEP and SMAP without EPT

The comment in code had it mostly right, but we enable paging for
emulated real mode regardless of EPT.

Without EPT (which implies emulated real mode), secondary VCPUs won't
start unless we disable SM[AE]P when the guest doesn't use paging.

Signed-off-by: Radim Krčmář <[email protected]>
---
arch/x86/kvm/vmx.c | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index b680c2e0e8a3..ab598558a7a4 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3788,20 +3788,21 @@ static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
if (!is_paging(vcpu)) {
hw_cr4 &= ~X86_CR4_PAE;
hw_cr4 |= X86_CR4_PSE;
- /*
- * SMEP/SMAP is disabled if CPU is in non-paging mode
- * in hardware. However KVM always uses paging mode to
- * emulate guest non-paging mode with TDP.
- * To emulate this behavior, SMEP/SMAP needs to be
- * manually disabled when guest switches to non-paging
- * mode.
- */
- hw_cr4 &= ~(X86_CR4_SMEP | X86_CR4_SMAP);
} else if (!(cr4 & X86_CR4_PAE)) {
hw_cr4 &= ~X86_CR4_PAE;
}
}

+ if (!enable_unrestricted_guest && !is_paging(vcpu))
+ /*
+ * SMEP/SMAP is disabled if CPU is in non-paging mode in
+ * hardware. However KVM always uses paging mode without
+ * unrestricted guest.
+ * To emulate this behavior, SMEP/SMAP needs to be manually
+ * disabled when guest switches to non-paging mode.
+ */
+ hw_cr4 &= ~(X86_CR4_SMEP | X86_CR4_SMAP);
+
vmcs_writel(CR4_READ_SHADOW, cr4);
vmcs_writel(GUEST_CR4, hw_cr4);
return 0;
--
2.5.3

2015-11-03 09:45:35

by Paolo Bonzini

Subject: Re: [PATCH] KVM: VMX: fix SMEP and SMAP without EPT

On 02/11/2015 22:20, Radim Krčmář wrote:
> The comment in code had it mostly right, but we enable paging for
> emulated real mode regardless of EPT.
>
> Without EPT (which implies emulated real mode), secondary VCPUs won't
> start unless we disable SM[AE]P when the guest doesn't use paging.
>
> Signed-off-by: Radim Krčmář <[email protected]>
> ---
> arch/x86/kvm/vmx.c | 19 ++++++++++---------
> 1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index b680c2e0e8a3..ab598558a7a4 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3788,20 +3788,21 @@ static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
> if (!is_paging(vcpu)) {
> hw_cr4 &= ~X86_CR4_PAE;
> hw_cr4 |= X86_CR4_PSE;
> - /*
> - * SMEP/SMAP is disabled if CPU is in non-paging mode
> - * in hardware. However KVM always uses paging mode to
> - * emulate guest non-paging mode with TDP.
> - * To emulate this behavior, SMEP/SMAP needs to be
> - * manually disabled when guest switches to non-paging
> - * mode.
> - */
> - hw_cr4 &= ~(X86_CR4_SMEP | X86_CR4_SMAP);
> } else if (!(cr4 & X86_CR4_PAE)) {
> hw_cr4 &= ~X86_CR4_PAE;
> }
> }
>
> + if (!enable_unrestricted_guest && !is_paging(vcpu))
> + /*
> + * SMEP/SMAP is disabled if CPU is in non-paging mode in
> + * hardware. However KVM always uses paging mode without
> + * unrestricted guest.
> + * To emulate this behavior, SMEP/SMAP needs to be manually
> + * disabled when guest switches to non-paging mode.
> + */
> + hw_cr4 &= ~(X86_CR4_SMEP | X86_CR4_SMAP);
> +
> vmcs_writel(CR4_READ_SHADOW, cr4);
> vmcs_writel(GUEST_CR4, hw_cr4);
> return 0;
>

Applied with Cc: [email protected].

Paolo