[PATCH] KVM: x86: Mark CR4.UMIP as reserved based on associated CPUID bit

[PATCH] KVM: x86: Mark CR4.UMIP as reserved based on associated CPUID bit

[Sean Christopherson]

Re-add code to mark CR4.UMIP as reserved if UMIP is not supported by the
host.  The UMIP handling was unintentionally dropped during a recent
refactoring.

Not flagging CR4.UMIP allows the guest to set its CR4.UMIP regardless of
host support or userspace desires.  On CPUs with UMIP support, including
emulated UMIP, this allows the guest to enable UMIP against the wishes
of the userspace VMM.  On CPUs without any form of UMIP, this results in
a failed VM-Enter due to invalid guest state.

Fixes: 345599f9a2928 ("KVM: x86: Add macro to ensure reserved cr4 bits checks stay in sync")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/x86.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7e3f1d937224..e70d1215638a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -898,6 +898,8 @@ EXPORT_SYMBOL_GPL(kvm_set_xcr);
 		__reserved_bits |= X86_CR4_PKE;		\
 	if (!__cpu_has(__c, X86_FEATURE_LA57))		\
 		__reserved_bits |= X86_CR4_LA57;	\
+	if (!__cpu_has(__c, X86_FEATURE_UMIP))		\
+		__reserved_bits |= X86_CR4_UMIP;	\
 	__reserved_bits;				\
 })
 
-- 
2.24.1

Re: [PATCH] KVM: x86: Mark CR4.UMIP as reserved based on associated CPUID bit

[Vitaly Kuznetsov]

Sean Christopherson <sean.j.christopherson@intel.com> writes:

> Re-add code to mark CR4.UMIP as reserved if UMIP is not supported by the
> host.  The UMIP handling was unintentionally dropped during a recent
> refactoring.
>
> Not flagging CR4.UMIP allows the guest to set its CR4.UMIP regardless of
> host support or userspace desires.  On CPUs with UMIP support, including
> emulated UMIP, this allows the guest to enable UMIP against the wishes
> of the userspace VMM.  On CPUs without any form of UMIP, this results in
> a failed VM-Enter due to invalid guest state.
>
> Fixes: 345599f9a2928 ("KVM: x86: Add macro to ensure reserved cr4 bits checks stay in sync")

This one in only in kvm/next so just in case another force-push is
around the corner I'd suggest we squash this change in :-)

> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/kvm/x86.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7e3f1d937224..e70d1215638a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -898,6 +898,8 @@ EXPORT_SYMBOL_GPL(kvm_set_xcr);
>  		__reserved_bits |= X86_CR4_PKE;		\
>  	if (!__cpu_has(__c, X86_FEATURE_LA57))		\
>  		__reserved_bits |= X86_CR4_LA57;	\
> +	if (!__cpu_has(__c, X86_FEATURE_UMIP))		\
> +		__reserved_bits |= X86_CR4_UMIP;	\
>  	__reserved_bits;				\
>  })

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

-- 
Vitaly

Re: [PATCH] KVM: x86: Mark CR4.UMIP as reserved based on associated CPUID bit

[Paolo Bonzini]

On 29/01/20 00:53, Sean Christopherson wrote:
> Re-add code to mark CR4.UMIP as reserved if UMIP is not supported by the
> host.  The UMIP handling was unintentionally dropped during a recent
> refactoring.
> 
> Not flagging CR4.UMIP allows the guest to set its CR4.UMIP regardless of
> host support or userspace desires.  On CPUs with UMIP support, including
> emulated UMIP, this allows the guest to enable UMIP against the wishes
> of the userspace VMM.  On CPUs without any form of UMIP, this results in
> a failed VM-Enter due to invalid guest state.
> 
> Fixes: 345599f9a2928 ("KVM: x86: Add macro to ensure reserved cr4 bits checks stay in sync")
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/kvm/x86.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7e3f1d937224..e70d1215638a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -898,6 +898,8 @@ EXPORT_SYMBOL_GPL(kvm_set_xcr);
>  		__reserved_bits |= X86_CR4_PKE;		\
>  	if (!__cpu_has(__c, X86_FEATURE_LA57))		\
>  		__reserved_bits |= X86_CR4_LA57;	\
> +	if (!__cpu_has(__c, X86_FEATURE_UMIP))		\
> +		__reserved_bits |= X86_CR4_UMIP;	\
>  	__reserved_bits;				\
>  })
>  
> 

Queued, thanks.

Paolo