arm/arm64: KVM: Enforce Break-Before-Make on Stage-2 page tables

The ARM architecture mandates that when changing a page table entry
from a valid entry to another valid entry, an invalid entry is first
written, TLB invalidated, and only then the new entry being written.

The current code doesn't respect this, directly writing the new
entry and only then invalidating TLBs. Let's fix it up.

Cc: <stable@vger.kernel.org>
Reported-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

1 files changed, 11 insertions, 6 deletions

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 42eefab3e8e1..74b5d199f6b7 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -910,11 +910,14 @@ static int stage2_set_pmd_huge(struct kvm *kvm, struct kvm_mmu_memory_cache
         VM_BUG_ON(pmd_present(*pmd) && pmd_pfn(*pmd) != pmd_pfn(*new_pmd));
 
         old_pmd = *pmd;
-        kvm_set_pmd(pmd, *new_pmd);
-        if (pmd_present(old_pmd))
+        if (pmd_present(old_pmd)) {
+                pmd_clear(pmd);
                 kvm_tlb_flush_vmid_ipa(kvm, addr);
-        else
+        } else {
                 get_page(virt_to_page(pmd));
+        }
+
+        kvm_set_pmd(pmd, *new_pmd);
         return 0;
 }
 
@@ -963,12 +966,14 @@ static int stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
 
         /* Create 2nd stage page table mapping - Level 3 */
         old_pte = *pte;
-        kvm_set_pte(pte, *new_pte);
-        if (pte_present(old_pte))
+        if (pte_present(old_pte)) {
+                kvm_set_pte(pte, __pte(0));
                 kvm_tlb_flush_vmid_ipa(kvm, addr);
-        else
+        } else {
                 get_page(virt_to_page(pte));
+        }
 
+        kvm_set_pte(pte, *new_pte);
         return 0;
 }