MIPS: KVM: Add missing gfn range check

kvm_mips_handle_mapped_seg_tlb_fault() calculates the guest frame number
based on the guest TLB EntryLo values, however it is not range checked
to ensure it lies within the guest_pmap. If the physical memory the
guest refers to is out of range then dump the guest TLB and emit an
internal error.

Fixes: 858dd5d4 ("KVM/MIPS32: MMU/TLB operations for the Guest.")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Cc: <stable@vger.kernel.org> # 3.10.x-
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

arch/mips/kvm/mmu.c

@@ -138,6 +138,7 @@ int kvm_mips_handle_mapped_seg_tlb_fault(struct kvm_vcpu *vcpu,
 	unsigned long entryhi = 0, entrylo0 = 0, entrylo1 = 0;
 	struct kvm *kvm = vcpu->kvm;
 	kvm_pfn_t pfn0, pfn1;
+	gfn_t gfn0, gfn1;
 	long tlb_lo[2];
 	int ret;
 
@@ -152,18 +153,24 @@ int kvm_mips_handle_mapped_seg_tlb_fault(struct kvm_vcpu *vcpu,
 			VPN2_MASK & (PAGE_MASK << 1)))
 		tlb_lo[(KVM_GUEST_COMMPAGE_ADDR >> PAGE_SHIFT) & 1] = 0;
 
-	if (kvm_mips_map_page(kvm, mips3_tlbpfn_to_paddr(tlb_lo[0])
-				   >> PAGE_SHIFT) < 0)
+	gfn0 = mips3_tlbpfn_to_paddr(tlb_lo[0]) >> PAGE_SHIFT;
+	gfn1 = mips3_tlbpfn_to_paddr(tlb_lo[1]) >> PAGE_SHIFT;
+	if (gfn0 >= kvm->arch.guest_pmap_npages ||
+	    gfn1 >= kvm->arch.guest_pmap_npages) {
+		kvm_err("%s: Invalid gfn: [%#llx, %#llx], EHi: %#lx\n",
+			__func__, gfn0, gfn1, tlb->tlb_hi);
+		kvm_mips_dump_guest_tlbs(vcpu);
+		return -1;
+	}
+
+	if (kvm_mips_map_page(kvm, gfn0) < 0)
 		return -1;
 
-	if (kvm_mips_map_page(kvm, mips3_tlbpfn_to_paddr(tlb_lo[1])
-				   >> PAGE_SHIFT) < 0)
+	if (kvm_mips_map_page(kvm, gfn1) < 0)
 		return -1;
 
-	pfn0 = kvm->arch.guest_pmap[
-		mips3_tlbpfn_to_paddr(tlb_lo[0]) >> PAGE_SHIFT];
-	pfn1 = kvm->arch.guest_pmap[
-		mips3_tlbpfn_to_paddr(tlb_lo[1]) >> PAGE_SHIFT];
+	pfn0 = kvm->arch.guest_pmap[gfn0];
+	pfn1 = kvm->arch.guest_pmap[gfn1];
 
 	/* Get attributes from the Guest TLB */
 	entrylo0 = mips3_paddr_to_tlbpfn(pfn0 << PAGE_SHIFT) |