Re: [PATCH V2] KVM/x86: Check input paging mode when cs.l is set

[Paolo Bonzini]

On 14/12/2017 04:55, Lan Tianyu wrote:
> +      * When EFER.LME and CR0.PG are set, CR4.PAE and EFER.LMA
> +      * must be set.
> +      */
> +     if ((sregs->efer & EFER_LME) && (sregs->cr0 & X86_CR0_PG_BIT)) {
> +             if (!(sregs->cr4 & X86_CR4_PAE_BIT))
> +                     return -EINVAL;
> +             if (!(sregs->efer & EFER_LMA))
> +                     return -EINVAL;
> +     } else if (sregs->efer & EFER_LMA)

This can just be "(sregs->efer & EFER_LMA) || sregs->cs.l", making the
next "if" redundant.  Even better written as

        if ((sregs->efer & EFER_LME) && (sregs->cr0 & X86_CR0_PG_BIT)) {
                /*
                 * When EFER.LME and CR0.PG are set, the processor is in
                 * 64-bit mode (though maybe in a 32-bit code segment).
                 * CR4.PAE and EFER.LMA must be set.
                 */
                if (... || ...)
                        return -EINVAL;
        } else {
                /*
                 * Not in 64-bit mode: EFER.LMA is clear and the code
                 * segment cannot be 64-bit.
                 */
                if (... || ...)
                        return -EINVAL;
        }

Paolo

> +             return -EINVAL;
> +
> +     /* When CS.L is set, vcpu should run in 64-bit mode. */
> +     if (sregs->cs.l)
> +             if (!((sregs->cr0 & X86_CR0_PG_BIT) &&
> +                   (sregs->cr4 & X86_CR4_PAE_BIT) &&
> +                   (sregs->efer & EFER_LME)))
> +                     return -EINVAL;