Re: [PATCH 4/4] KVM: Disable SMAP for guests in EPT realmode and EPT unpaging mode

[Jan Kiszka]

On 2014-03-27 13:25, Feng Wu wrote:
> 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, SMAP needs to be
> manually disabled when guest switches to non-paging mode.
> 
> Signed-off-by: Feng Wu <feng...@intel.com>
> ---
>  arch/x86/kvm/vmx.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index dcc4de3..1d37e50 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3421,13 +3421,15 @@ static int vmx_set_cr4(struct kvm_vcpu *vcpu, 
> unsigned long cr4)
>                       hw_cr4 &= ~X86_CR4_PAE;
>                       hw_cr4 |= X86_CR4_PSE;
>                       /*
> -                      * SMEP is disabled if CPU is in non-paging mode in
> -                      * hardware. However KVM always uses paging mode to
> +                      * 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 needs to be manually
> -                      * disabled when guest switches to non-paging mode.
> +                      * To emulate this behavior, SMEP/SMAP needs to be
> +                      * manually disabled when guest switches to non-paging
> +                      * mode.
>                        */
>                       hw_cr4 &= ~X86_CR4_SMEP;
> +                     hw_cr4 &= ~X86_CR4_SMAP;

Why not

hw_cr4 &= ~(X86_CR4_SMEP | X86_CR4_SMAP);

?

Jan

>               } else if (!(cr4 & X86_CR4_PAE)) {
>                       hw_cr4 &= ~X86_CR4_PAE;
>               }
> 

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