From 0577d1abe704c315bb5cdfc71f4ca7b9b5358f59 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Tue, 18 Feb 2020 13:07:31 -0800 Subject: KVM: Terminate memslot walks via used_slots Refactor memslot handling to treat the number of used slots as the de facto size of the memslot array, e.g. return NULL from id_to_memslot() when an invalid index is provided instead of relying on npages==0 to detect an invalid memslot. Rework the sorting and walking of memslots in advance of dynamically sizing memslots to aid bisection and debug, e.g. with luck, a bug in the refactoring will bisect here and/or hit a WARN instead of randomly corrupting memory. Alternatively, a global null/invalid memslot could be returned, i.e. so callers of id_to_memslot() don't have to explicitly check for a NULL memslot, but that approach runs the risk of introducing difficult-to- debug issues, e.g. if the global null slot is modified. Constifying the return from id_to_memslot() to combat such issues is possible, but would require a massive refactoring of arch specific code and would still be susceptible to casting shenanigans. Add function comments to update_memslots() and search_memslots() to explicitly (and loudly) state how memslots are sorted. Opportunistically stuff @hva with a non-canonical value when deleting a private memslot on x86 to detect bogus usage of the freed slot. No functional change intended. Tested-by: Christoffer Dall Tested-by: Marc Zyngier Signed-off-by: Sean Christopherson Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) (limited to 'arch/x86/kvm/x86.c') diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 27b97e546980..13ac4d0f9794 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -9715,9 +9715,9 @@ void kvm_arch_sync_events(struct kvm *kvm) int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size) { int i, r; - unsigned long hva; + unsigned long hva, uninitialized_var(old_npages); struct kvm_memslots *slots = kvm_memslots(kvm); - struct kvm_memory_slot *slot, old; + struct kvm_memory_slot *slot; /* Called with kvm->slots_lock held. */ if (WARN_ON(id >= KVM_MEM_SLOTS_NUM)) @@ -9725,7 +9725,7 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size) slot = id_to_memslot(slots, id); if (size) { - if (slot->npages) + if (slot && slot->npages) return -EEXIST; /* @@ -9737,13 +9737,14 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size) if (IS_ERR((void *)hva)) return PTR_ERR((void *)hva); } else { - if (!slot->npages) + if (!slot || !slot->npages) return 0; - hva = 0; + /* Stuff a non-canonical value to catch use-after-delete. */ + hva = 0xdeadull << 48; + old_npages = slot->npages; } - old = *slot; for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { struct kvm_userspace_memory_region m; @@ -9758,7 +9759,7 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size) } if (!size) - vm_munmap(old.userspace_addr, old.npages * PAGE_SIZE); + vm_munmap(hva, old_npages * PAGE_SIZE); return 0; } -- cgit v1.2.3