From: Sean Christopherson seanjc@google.com
commit bda44d844758c70c8dc1478e6fc9c25efa90c5a7 upstream.
When modifying memslots, snapshot the "old" memslot and copy it to the "new" memslot's arch data after (re)acquiring slots_arch_lock. x86 can change a memslot's arch data while memslot updates are in-progress so long as it holds slots_arch_lock, thus snapshotting a memslot without holding the lock can result in the consumption of stale data.
Fixes: b10a038e84d1 ("KVM: mmu: Add slots_arch_lock for memslot arch fields") Cc: stable@vger.kernel.org Cc: Ben Gardon bgardon@google.com Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20211104002531.1176691-2-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- virt/kvm/kvm_main.c | 47 +++++++++++++++++++++++++++++++---------------- 1 file changed, 31 insertions(+), 16 deletions(-)
--- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1523,11 +1523,10 @@ static struct kvm_memslots *kvm_dup_mems
static int kvm_set_memslot(struct kvm *kvm, const struct kvm_userspace_memory_region *mem, - struct kvm_memory_slot *old, struct kvm_memory_slot *new, int as_id, enum kvm_mr_change change) { - struct kvm_memory_slot *slot; + struct kvm_memory_slot *slot, old; struct kvm_memslots *slots; int r;
@@ -1558,7 +1557,7 @@ static int kvm_set_memslot(struct kvm *k * Note, the INVALID flag needs to be in the appropriate entry * in the freshly allocated memslots, not in @old or @new. */ - slot = id_to_memslot(slots, old->id); + slot = id_to_memslot(slots, new->id); slot->flags |= KVM_MEMSLOT_INVALID;
/* @@ -1589,6 +1588,26 @@ static int kvm_set_memslot(struct kvm *k kvm_copy_memslots(slots, __kvm_memslots(kvm, as_id)); }
+ /* + * Make a full copy of the old memslot, the pointer will become stale + * when the memslots are re-sorted by update_memslots(), and the old + * memslot needs to be referenced after calling update_memslots(), e.g. + * to free its resources and for arch specific behavior. This needs to + * happen *after* (re)acquiring slots_arch_lock. + */ + slot = id_to_memslot(slots, new->id); + if (slot) { + old = *slot; + } else { + WARN_ON_ONCE(change != KVM_MR_CREATE); + memset(&old, 0, sizeof(old)); + old.id = new->id; + old.as_id = as_id; + } + + /* Copy the arch-specific data, again after (re)acquiring slots_arch_lock. */ + memcpy(&new->arch, &old.arch, sizeof(old.arch)); + r = kvm_arch_prepare_memory_region(kvm, new, mem, change); if (r) goto out_slots; @@ -1596,14 +1615,18 @@ static int kvm_set_memslot(struct kvm *k update_memslots(slots, new, change); slots = install_new_memslots(kvm, as_id, slots);
- kvm_arch_commit_memory_region(kvm, mem, old, new, change); + kvm_arch_commit_memory_region(kvm, mem, &old, new, change); + + /* Free the old memslot's metadata. Note, this is the full copy!!! */ + if (change == KVM_MR_DELETE) + kvm_free_memslot(kvm, &old);
kvfree(slots); return 0;
out_slots: if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) { - slot = id_to_memslot(slots, old->id); + slot = id_to_memslot(slots, new->id); slot->flags &= ~KVM_MEMSLOT_INVALID; slots = install_new_memslots(kvm, as_id, slots); } else { @@ -1618,7 +1641,6 @@ static int kvm_delete_memslot(struct kvm struct kvm_memory_slot *old, int as_id) { struct kvm_memory_slot new; - int r;
if (!old->npages) return -EINVAL; @@ -1631,12 +1653,7 @@ static int kvm_delete_memslot(struct kvm */ new.as_id = as_id;
- r = kvm_set_memslot(kvm, mem, old, &new, as_id, KVM_MR_DELETE); - if (r) - return r; - - kvm_free_memslot(kvm, old); - return 0; + return kvm_set_memslot(kvm, mem, &new, as_id, KVM_MR_DELETE); }
/* @@ -1711,7 +1728,6 @@ int __kvm_set_memory_region(struct kvm * if (!old.npages) { change = KVM_MR_CREATE; new.dirty_bitmap = NULL; - memset(&new.arch, 0, sizeof(new.arch)); } else { /* Modify an existing slot. */ if ((new.userspace_addr != old.userspace_addr) || (new.npages != old.npages) || @@ -1725,9 +1741,8 @@ int __kvm_set_memory_region(struct kvm * else /* Nothing to change. */ return 0;
- /* Copy dirty_bitmap and arch from the current memslot. */ + /* Copy dirty_bitmap from the current memslot. */ new.dirty_bitmap = old.dirty_bitmap; - memcpy(&new.arch, &old.arch, sizeof(new.arch)); }
if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) { @@ -1753,7 +1768,7 @@ int __kvm_set_memory_region(struct kvm * bitmap_set(new.dirty_bitmap, 0, new.npages); }
- r = kvm_set_memslot(kvm, mem, &old, &new, as_id, change); + r = kvm_set_memslot(kvm, mem, &new, as_id, change); if (r) goto out_bitmap;