diff options
| author | Sean Christopherson <seanjc@google.com> | 2024-01-09 16:42:39 -0800 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2024-01-29 08:16:58 -0800 |
| commit | d489ec95658392a000dd26fba511eec1900245b0 (patch) | |
| tree | f6795331c52740b72c6a60156a43fdfe289624b3 /virt | |
| parent | 41bccc98fb7931d63d03f326a746ac4d429c1dd3 (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.c | 4 |
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); /* |