Re: [Xen-devel] [PATCH v2 4/7] VMX: Disable SMAP feature when guest is in non-paging mode

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 23/04/14 15:36, Feng Wu wrote:
> SMAP is disabled if CPU is in non-paging mode in hardware.
> However Xen always uses paging mode to emulate guest non-paging
> mode with HAP. To emulate this behavior, SMAP needs to be manually
> disabled when guest switches to non-paging mode.
>
> This logic is similiar with SMEP.
>
> Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>

Reviewed-by: Andrew Cooper<andrew.cooper3@xxxxxxxxxx>

> ---
>  xen/arch/x86/hvm/vmx/vmx.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index 94f3db2..79dd272 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -1310,12 +1310,12 @@ static void vmx_update_guest_cr(struct vcpu *v, 
> unsigned int cr)
>          if ( !hvm_paging_enabled(v) )
>          {
>              /*
> -             * SMEP is disabled if CPU is in non-paging mode in hardware.
> +             * SMEP/SMAP is disabled if CPU is in non-paging mode in 
> hardware.
>               * However Xen always uses paging mode to emulate guest 
> non-paging
> -             * mode. To emulate this behavior, SMEP needs to be manually
> +             * mode. To emulate this behavior, SMEP/SMAP needs to be manually
>               * disabled when guest VCPU is in non-paging mode.
>               */
> -            v->arch.hvm_vcpu.hw_cr[4] &= ~X86_CR4_SMEP;
> +            v->arch.hvm_vcpu.hw_cr[4] &= ~(X86_CR4_SMEP | X86_CR4_SMAP);
>          }
>          __vmwrite(GUEST_CR4, v->arch.hvm_vcpu.hw_cr[4]);
>          break;


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