Re: [PATCH v2 4/6] KVM: x86: Introduce KVM_GET_SREGS2 / KVM_SET_SREGS2

[Paolo Bonzini]

On 26/04/21 13:13, Maxim Levitsky wrote:
> +	if (sregs2->flags & KVM_SREGS2_FLAGS_PDPTRS_VALID) {
> +
> +		if (!is_pae_paging(vcpu))
> +			return -EINVAL;
> +
> +		for (i = 0 ; i < 4 ; i++)
> +			kvm_pdptr_write(vcpu, i, sregs2->pdptrs[i]);
> +
> +		kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);
> +		mmu_reset_needed = 1;
> +	}

I think this should also have

	else {
		if (is_pae_paging(vcpu))
			return -EINVAL;
	}

but perhaps even better, check it at the beginning:

	if ((sregs->cr4 & X86_CR4_PAE) &&
            !!(sregs->efer & EFER_LMA) == !!(sregs2->flags & KVM_SREGS2_FLAGS_PDPTRS_VALID))
		return -EINVAL;

which technically means the flag is redundant, but there is some value in
having the flag and not allowing the user to shoot itself in the foot.

Paolo