Re: [Xen-devel] [PATCH] x86emul: correct PUSHF/POPF

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 06/12/16 13:25, Jan Beulich wrote:
> Both need to raise #GP(0) when in VM86 mode with IOPL < 3.
>
> Additionally PUSHF is documented to clear VM and RF from the value
> placed onto the stack.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -3121,13 +3121,20 @@ x86_emulate(
>      }
>  
>      case 0x9c: /* pushf */
> -        src.val = _regs.eflags;
> +        generate_exception_if((_regs.eflags & EFLG_VM) &&
> +                              (_regs.eflags & EFLG_IOPL) != EFLG_IOPL,

How about "MASK_EXTR(_regs.eflags, EFLG_IOPL) != 3"

This would be rather clear to read, as the two EFLG_IOPL have two
different purposes in the line as presented.

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

> +                              EXC_GP, 0);
> +        src.val = _regs.eflags & ~(EFLG_VM | EFLG_RF);
>          goto push;
>  
>      case 0x9d: /* popf */ {
>          uint32_t mask = EFLG_VIP | EFLG_VIF | EFLG_VM;
> +
>          if ( !mode_ring0() )
>          {
> +            generate_exception_if((_regs.eflags & EFLG_VM) &&
> +                                  (_regs.eflags & EFLG_IOPL) != EFLG_IOPL,
> +                                  EXC_GP, 0);
>              mask |= EFLG_IOPL;
>              if ( !mode_iopl() )
>                  mask |= EFLG_IF;
>
>
>


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