arm/arm64: KVM: Ensure memslots are within KVM_PHYS_SIZE

When creating or moving a memslot, make sure the IPA space is within the
addressable range of the guest.  Otherwise, user space can create too
large a memslot and KVM would try to access potentially unallocated page
table entries when inserting entries in the Stage-2 page tables.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index ee142edcca84..8c40829d4a52 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -1003,6 +1003,9 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
                 goto out_unlock;
         }
 
+        /* Userspace should not be able to register out-of-bounds IPAs */
+        VM_BUG_ON(fault_ipa >= KVM_PHYS_SIZE);
+
         ret = user_mem_abort(vcpu, fault_ipa, memslot, hva, fault_status);
         if (ret == 0)
                 ret = 1;
@@ -1229,6 +1232,14 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
                 return 0;
 
         /*
+         * Prevent userspace from creating a memory region outside of the IPA
+         * space addressable by the KVM guest IPA space.
+         */
+        if (memslot->base_gfn + memslot->npages >=
+            (KVM_PHYS_SIZE >> PAGE_SHIFT))
+                return -EFAULT;
+
+        /*
          * A memory region could potentially cover multiple VMAs, and any holes
          * between them, so iterate over all of them to find out if we can map
          * any of them right now.