Re: [Xen-devel] [PATCH v3 16/25] x86emul: support SWAPGS

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 07/12/17 14:11, Jan Beulich wrote:
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v3: New.
>
> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -5047,6 +5047,24 @@ x86_emulate(
>                  goto done;
>              break;
>  
> +        case 0xf8: /* swapgs */
> +            generate_exception_if(!mode_64bit(), EXC_UD);
> +            generate_exception_if(!mode_ring0(), EXC_GP, 0);
> +            fail_if(!ops->read_segment || !ops->read_msr ||
> +                    !ops->write_segment || !ops->write_msr);
> +            if ( (rc = ops->read_segment(x86_seg_gs, &sreg,
> +                                         ctxt)) != X86EMUL_OKAY ||
> +                 (rc = ops->read_msr(MSR_SHADOW_GS_BASE, &msr_val,
> +                                     ctxt)) != X86EMUL_OKAY ||
> +                 (rc = ops->write_msr(MSR_SHADOW_GS_BASE, sreg.base,
> +                                      ctxt)) != X86EMUL_OKAY )

We need to unwind this write in the case of write_segment failing, or
when the instruction restarts, state will be corrupt.

~Andrew

> +                goto done;
> +            sreg.base = msr_val;
> +            if ( (rc = ops->write_segment(x86_seg_gs, &sreg,
> +                                          ctxt)) != X86EMUL_OKAY )
> +                goto done;
> +            break;
> +
>          case 0xf9: /* rdtscp */
>              fail_if(ops->read_msr == NULL);
>              if ( (rc = ops->read_msr(MSR_TSC_AUX,
>
>
>


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