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authorPaolo Bonzini <pbonzini@redhat.com>2022-04-08 13:09:04 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2022-04-08 14:20:36 -1000
commit01e67e04c28170c47700c2c226d732bbfedb1ad0 (patch)
treec6bb531bdfd0459b88e2777ca429dfe0cb666df5
parenta431dbbc540532b7465eae4fc8b56a85a9fc7d17 (diff)
mmmremap.c: avoid pointless invalidate_range_start/end on mremap(old_size=0)
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 <pbonzini@redhat.com> Cc: Sean Christopherson <seanjc@google.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/mremap.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/mm/mremap.c b/mm/mremap.c
index 9d76da79594d..303d3290b938 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -486,6 +486,9 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
pmd_t *old_pmd, *new_pmd;
pud_t *old_pud, *new_pud;
+ if (!len)
+ return 0;
+
old_end = old_addr + len;
flush_cache_range(vma, old_addr, old_end);