From 7d659cb1763ff17d1c6ee082fa6feb4267c7a30b Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Fri, 8 Apr 2022 13:09:04 -0700 Subject: mmmremap.c: avoid pointless invalidate_range_start/end on mremap(old_size=0) commit 01e67e04c28170c47700c2c226d732bbfedb1ad0 upstream. If an mremap() syscall with old_size=0 ends up in move_page_tables(), it will call invalidate_range_start()/invalidate_range_end() unnecessarily, i.e. with an empty range. This causes a WARN in KVM's mmu_notifier. In the past, empty ranges have been diagnosed to be off-by-one bugs, hence the WARNing. Given the low (so far) number of unique reports, the benefits of detecting more buggy callers seem to outweigh the cost of having to fix cases such as this one, where userspace is doing something silly. In this particular case, an early return from move_page_tables() is enough to fix the issue. Link: https://lkml.kernel.org/r/20220329173155.172439-1-pbonzini@redhat.com Reported-by: syzbot+6bde52d89cfdf9f61425@syzkaller.appspotmail.com Signed-off-by: Paolo Bonzini Cc: Sean Christopherson Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/mremap.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'mm') diff --git a/mm/mremap.c b/mm/mremap.c index 138abbae4f75..d4c8d6cca3f4 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -260,6 +260,9 @@ unsigned long move_page_tables(struct vm_area_struct *vma, struct mmu_notifier_range range; pmd_t *old_pmd, *new_pmd; + if (!len) + return 0; + old_end = old_addr + len; flush_cache_range(vma, old_addr, old_end); -- cgit v1.2.3