KVM: arm64: Reject shared table walks in the hyp code

Exclusive table walks are the only supported table walk in the hyp, as
there is no construct like RCU available in the hypervisor code. Reject
any attempt to do a shared table walk by returning an error and allowing
the caller to clean up the mess.

Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221118182222.3932898-4-oliver.upton@linux.dev

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 4b6b52ebc11c3e70abd1a0ea67ec995730383f29..d5cb01f8dc0669d3b7f50074b5b2f1a4d372744b 100644 (file)
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -229,7 +229,18 @@ static inline kvm_pte_t *kvm_dereference_pteref(struct kvm_pgtable_walker *walke
        return pteref;
 }
 
-static inline void kvm_pgtable_walk_begin(struct kvm_pgtable_walker *walker) {}
+static inline int kvm_pgtable_walk_begin(struct kvm_pgtable_walker *walker)
+{
+       /*
+        * Due to the lack of RCU (or a similar protection scheme), only
+        * non-shared table walkers are allowed in the hypervisor.
+        */
+       if (walker->flags & KVM_PGTABLE_WALK_SHARED)
+               return -EPERM;
+
+       return 0;
+}
+
 static inline void kvm_pgtable_walk_end(struct kvm_pgtable_walker *walker) {}
 
 static inline bool kvm_pgtable_walk_lock_held(void)
@@ -247,10 +258,12 @@ static inline kvm_pte_t *kvm_dereference_pteref(struct kvm_pgtable_walker *walke
        return rcu_dereference_check(pteref, !(walker->flags & KVM_PGTABLE_WALK_SHARED));
 }
 
-static inline void kvm_pgtable_walk_begin(struct kvm_pgtable_walker *walker)
+static inline int kvm_pgtable_walk_begin(struct kvm_pgtable_walker *walker)
 {
        if (walker->flags & KVM_PGTABLE_WALK_SHARED)
                rcu_read_lock();
+
+       return 0;
 }
 
 static inline void kvm_pgtable_walk_end(struct kvm_pgtable_walker *walker)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index d6f3753cb87ed600c9ba8dbff76e9a9395d2e15c..58dbe0ab567fe2e8c7f176b2f65968848b0e59fe 100644 (file)
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -289,7 +289,10 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
        };
        int r;
 
-       kvm_pgtable_walk_begin(walker);
+       r = kvm_pgtable_walk_begin(walker);
+       if (r)
+               return r;
+
        r = _kvm_pgtable_walk(pgt, &walk_data);
        kvm_pgtable_walk_end(walker);