[PATCH 3/4] KVM: x86: Reject KVM_CREATE_IRQCHIP if APIC base is already mapped

[Tim Wiederhake]

User space must not map guest memory that covers the default APIC base
address (0xfee00000) when using an in-kernel irqchip.  Currently,
KVM_CREATE_IRQCHIP does not check for this.  The violation goes
unnoticed until vcpu creation, which fails with the misleading error
-EEXIST.

Add an explicit check to KVM_CREATE_IRQCHIP so the conflict is reported
at the point where the constraint takes effect.

Signed-off-by: Tim Wiederhake <twiederh@xxxxxxxxxx>
---
 arch/x86/kvm/x86.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0550359ed798..07f348232a72 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7336,6 +7336,10 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
 		if (kvm->created_vcpus)
 			goto create_irqchip_unlock;
 
+		r = -EEXIST;
+		if (gfn_to_memslot(kvm, gpa_to_gfn(APIC_DEFAULT_PHYS_BASE)))
+			goto create_irqchip_unlock;
+
 		r = kvm_pic_init(kvm);
 		if (r)
 			goto create_irqchip_unlock;
-- 
2.52.0