Matt T. Yourst notes that kvm_arch_vcpu_ioctl_set_sregs lacks validity checking for the new cr3 value: "Userspace callers of KVM_SET_SREGS can pass a bogus value of cr3 to the kernel. This will trigger a NULL pointer access in gfn_to_rmap() when userspace next tries to call KVM_RUN on the affected VCPU and kvm attempts to activate the new non-existent page table root. This happens since kvm only validates that cr3 points to a valid guest physical memory page when code *inside* the guest sets cr3. However, kvm currently trusts the userspace caller (e.g. QEMU) on the host machine to always supply a valid page table root, rather than properly validating it along with the rest of the reloaded guest state." http://sourceforge.net/tracker/?func=detail&atid=893831&aid=2687641&group_id=180599 Follow Avi's suggestion to use kvm_set_cr3, and do the same for assigment of cr4. Note kvm_set_cr4 unconditionally resets the mmu context, as long as cr4 is valid. Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 148cde2..89fb3c7 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3985,25 +3985,19 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu, kvm_x86_ops->set_gdt(vcpu, &dt); vcpu->arch.cr2 = sregs->cr2; - mmu_reset_needed |= vcpu->arch.cr3 != sregs->cr3; - vcpu->arch.cr3 = sregs->cr3; + kvm_set_cr3(vcpu, sregs->cr3); kvm_set_cr8(vcpu, sregs->cr8); mmu_reset_needed |= vcpu->arch.shadow_efer != sregs->efer; kvm_x86_ops->set_efer(vcpu, sregs->efer); kvm_set_apic_base(vcpu, sregs->apic_base); - kvm_x86_ops->decache_cr4_guest_bits(vcpu); - mmu_reset_needed |= vcpu->arch.cr0 != sregs->cr0; kvm_x86_ops->set_cr0(vcpu, sregs->cr0); vcpu->arch.cr0 = sregs->cr0; - mmu_reset_needed |= vcpu->arch.cr4 != sregs->cr4; - kvm_x86_ops->set_cr4(vcpu, sregs->cr4); - if (!is_long_mode(vcpu) && is_pae(vcpu)) - load_pdptrs(vcpu, vcpu->arch.cr3); + kvm_set_cr4(vcpu, sregs->cr4); if (mmu_reset_needed) kvm_mmu_reset_context(vcpu); -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
