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authorSean Christopherson <seanjc@google.com>2024-01-09 16:42:39 -0800
committerSean Christopherson <seanjc@google.com>2024-01-29 08:16:58 -0800
commitd489ec95658392a000dd26fba511eec1900245b0 (patch)
treef6795331c52740b72c6a60156a43fdfe289624b3 /virt
parent41bccc98fb7931d63d03f326a746ac4d429c1dd3 (diff)
KVM: Harden against unpaired kvm_mmu_notifier_invalidate_range_end() calls
When handling the end of an mmu_notifier invalidation, WARN if mn_active_invalidate_count is already 0 do not decrement it further, i.e. avoid causing mn_active_invalidate_count to underflow/wrap. In the worst case scenario, effectively corrupting mn_active_invalidate_count could cause kvm_swap_active_memslots() to hang indefinitely. end() calls are *supposed* to be paired with start(), i.e. underflow can only happen if there is a bug elsewhere in the kernel, but due to lack of lockdep assertions in the mmu_notifier helpers, it's all too easy for a bug to go unnoticed for some time, e.g. see the recently introduced PAGEMAP_SCAN ioctl(). Ideally, mmu_notifiers would incorporate lockdep assertions, but users of mmu_notifiers aren't required to hold any one specific lock, i.e. adding the necessary annotations to make lockdep aware of all locks that are mutally exclusive with mm_take_all_locks() isn't trivial. Link: https://lore.kernel.org/all/000000000000f6d051060c6785bc@google.com Link: https://lore.kernel.org/r/20240110004239.491290-1-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
Diffstat (limited to 'virt')
-rw-r--r--virt/kvm/kvm_main.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 10bfc88a69f7..8f03b56dafbd 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -890,7 +890,9 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
/* Pairs with the increment in range_start(). */
spin_lock(&kvm->mn_invalidate_lock);
- wake = (--kvm->mn_active_invalidate_count == 0);
+ if (!WARN_ON_ONCE(!kvm->mn_active_invalidate_count))
+ --kvm->mn_active_invalidate_count;
+ wake = !kvm->mn_active_invalidate_count;
spin_unlock(&kvm->mn_invalidate_lock);
/*