Re: [Xen-devel] [PATCH 5/5] x86/PV: don't commit debug register values early in arch_set_info_guest()

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 12/10/2013 03:48 PM, Jan Beulich wrote:
> They're being taken care of later (via set_debugreg()), and temporarily
> copying them into struct vcpu means that bad values may end up getting
> loaded during context switch if the vCPU is already running and the
> function errors out between the premature and real commit step, leading
> to the same issue that XSA-12 dealt with.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Release-acked-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -740,11 +740,12 @@ int arch_set_info_guest(
>               XLAT_trap_info(v->arch.pv_vcpu.trap_ctxt + i,
>                              c.cmp->trap_ctxt + i);
>       }
> -    for ( i = 0; i < ARRAY_SIZE(v->arch.debugreg); ++i )
> -        v->arch.debugreg[i] = c(debugreg[i]);
>   
>       if ( has_hvm_container_vcpu(v) )
>       {
> +        for ( i = 0; i < ARRAY_SIZE(v->arch.debugreg); ++i )
> +            v->arch.debugreg[i] = c(debugreg[i]);
> +
>           /*
>            * NB: TF_kernel_mode is set unconditionally for HVM guests,
>            * so we always use the gs_base_kernel here. If we change this

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