From 0774a964ef561b7170d8d1b1bfe6f88002b6d219 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 20 Mar 2020 13:55:40 -0700 Subject: [PATCH] KVM: Fix out of range accesses to memslots Reset the LRU slot if it becomes invalid when deleting a memslot to fix an out-of-bounds/use-after-free access when searching through memslots. Explicitly check for there being no used slots in search_memslots(), and in the caller of s390's approximation variant. Fixes: 36947254e5f9 ("KVM: Dynamically size memslot array based on number of used slots") Reported-by: Qian Cai Cc: Peter Xu Signed-off-by: Sean Christopherson Message-Id: <20200320205546.2396-2-sean.j.christopherson@intel.com> Acked-by: Christian Borntraeger Signed-off-by: Paolo Bonzini --- arch/s390/kvm/kvm-s390.c | 3 +++ include/linux/kvm_host.h | 3 +++ virt/kvm/kvm_main.c | 3 +++ 3 files changed, 9 insertions(+) diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 807ed6d722dd..cb15fdda1fee 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -2002,6 +2002,9 @@ static int kvm_s390_get_cmma(struct kvm *kvm, struct kvm_s390_cmma_log *args, struct kvm_memslots *slots = kvm_memslots(kvm); struct kvm_memory_slot *ms; + if (unlikely(!slots->used_slots)) + return 0; + cur_gfn = kvm_s390_next_dirty_cmma(slots, args->start_gfn); ms = gfn_to_memslot(kvm, cur_gfn); args->count = 0; diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 35bc52e187a2..b19dee4ed7d9 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -1032,6 +1032,9 @@ search_memslots(struct kvm_memslots *slots, gfn_t gfn) int slot = atomic_read(&slots->lru_slot); struct kvm_memory_slot *memslots = slots->memslots; + if (unlikely(!slots->used_slots)) + return NULL; + if (gfn >= memslots[slot].base_gfn && gfn < memslots[slot].base_gfn + memslots[slot].npages) return &memslots[slot]; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 28eae681859f..f744bc603c53 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -882,6 +882,9 @@ static inline void kvm_memslot_delete(struct kvm_memslots *slots, slots->used_slots--; + if (atomic_read(&slots->lru_slot) >= slots->used_slots) + atomic_set(&slots->lru_slot, 0); + for (i = slots->id_to_index[memslot->id]; i < slots->used_slots; i++) { mslots[i] = mslots[i + 1]; slots->id_to_index[mslots[i].id] = i;