KVM: arm64: Reassign nested_mmus array behind mmu_lock

kvm->arch.nested_mmus[] is walked under kvm->mmu_lock, including from the
MMU notifier path (kvm_unmap_gfn_range() -> kvm_nested_s2_unmap()), which
can run at any time. kvm_vcpu_init_nested() reallocates the array and frees
the old buffer while holding only kvm->arch.config_lock, so such a walker
can reference the freed array.

Allocate the new array outside of mmu_lock, as the allocation can sleep.
Under the lock, copy the existing entries, fix up the back pointers and
reassign the array. Free the old buffer after dropping the lock, as
kvfree() can sleep as well.

Fixes: 4f128f8e1aaac ("KVM: arm64: nv: Support multiple nested Stage-2 mmu structures")
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Reviewed-by: Oliver Upton <oupton@kernel.org>
Link: https://patch.msgid.link/aiKIVVeIr1aAB1yp@v4bel
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: stable@vger,kernel.org

diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 38f672e9408787be6a774122bb27e9f82dc01f77..6f7bc9a9992e0efbfd4e8c7088c452409cfe4e5e 100644 (file)
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -89,21 +89,28 @@ int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu)
         * again, and there is no reason to affect the whole VM for this.
         */
        num_mmus = atomic_read(&kvm->online_vcpus) * S2_MMU_PER_VCPU;
-       tmp = kvrealloc(kvm->arch.nested_mmus,
-                       size_mul(sizeof(*kvm->arch.nested_mmus), num_mmus),
-                       GFP_KERNEL_ACCOUNT | __GFP_ZERO);
-       if (!tmp)
-               return -ENOMEM;
 
-       swap(kvm->arch.nested_mmus, tmp);
+       if (num_mmus > kvm->arch.nested_mmus_size) {
+               tmp = kvcalloc(num_mmus, sizeof(*tmp), GFP_KERNEL_ACCOUNT);
+               if (!tmp)
+                       return -ENOMEM;
 
-       /*
-        * If we went through a realocation, adjust the MMU back-pointers in
-        * the previously initialised kvm_pgtable structures.
-        */
-       if (kvm->arch.nested_mmus != tmp)
-               for (int i = 0; i < kvm->arch.nested_mmus_size; i++)
-                       kvm->arch.nested_mmus[i].pgt->mmu = &kvm->arch.nested_mmus[i];
+               write_lock(&kvm->mmu_lock);
+
+               if (kvm->arch.nested_mmus_size) {
+                       memcpy(tmp, kvm->arch.nested_mmus,
+                              size_mul(sizeof(*tmp), kvm->arch.nested_mmus_size));
+
+                       for (int i = 0; i < kvm->arch.nested_mmus_size; i++)
+                               tmp[i].pgt->mmu = &tmp[i];
+               }
+
+               swap(kvm->arch.nested_mmus, tmp);
+
+               write_unlock(&kvm->mmu_lock);
+
+               kvfree(tmp);
+       }
 
        for (int i = kvm->arch.nested_mmus_size; !ret && i < num_mmus; i++)
                ret = init_nested_s2_mmu(kvm, &kvm->arch.nested_mmus[i]);