[PATCH 4/4] KVM: x86: Reject user memory regions covering the APIC base

[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_SET_USER_MEMORY_REGION 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_arch_prepare_memory_region() so the
conflict is reported at the point where it is introduced.

Signed-off-by: Tim Wiederhake <twiederh@xxxxxxxxxx>
---
 arch/x86/kvm/x86.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 07f348232a72..b38d4355137a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -13684,12 +13684,19 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 		return -EINVAL;
 
 	if (change == KVM_MR_CREATE || change == KVM_MR_MOVE) {
+		const gfn_t apic_gfn = gpa_to_gfn(APIC_DEFAULT_PHYS_BASE);
+
 		if ((new->base_gfn + new->npages - 1) > kvm_mmu_max_gfn())
 			return -EINVAL;
 
 		if (kvm_is_gfn_alias(kvm, new->base_gfn + new->npages - 1))
 			return -EINVAL;
 
+		if (irqchip_in_kernel(kvm) &&
+		    new->base_gfn <= apic_gfn &&
+		    apic_gfn < new->base_gfn + new->npages)
+			return -EEXIST;
+
 		return kvm_alloc_memslot_metadata(kvm, new);
 	}
 
-- 
2.52.0