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

From: Paolo Bonzini
Date: Mon Apr 26 2021 - 08:32:38 EST


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