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 qsyhyeJL 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in kernel/fork.c is not only > > used for duplicating VMAs during fork(), but also for duplicating VMAs > > when splitting VMAs or when mremap()'ing them. > > > > VM_PFNMAP mappings can at least get ordinarily mremap()'ed (no change in > > size) and apparently also shrunk during mremap(), which implies > > duplicating the VMA in __split_vma() first. > > > > In case of ordinary mremap() (no change in size), we first duplicate the > > VMA in copy_vma_and_data()->copy_vma() to then call untrack_pfn_clear() on > > the old VMA: we effectively move the VM_PAT reservation. So the > > untrack_pfn_clear() call on the new VMA duplicating is wrong in that > > context. > > > > Splitting of VMAs seems problematic, because we don't duplicate/adjust the > > reservation when splitting the VMA. Instead, in memtype_erase() -- called > > during zapping/munmap -- we shrink a reservation in case only the end > > address matches: Assume we split a VMA into A and B, both would share a > > reservation until B is unmapped. > > > > So when unmapping B, the reservation would be updated to cover only A. When > > unmapping A, we would properly remove the now-shrunk reservation. That > > scenario describes the mremap() shrinking (old_size > new_size), where > > we split + unmap B, and the untrack_pfn_clear() on the new VMA when > > is wrong. > > > > What if we manage to split a VM_PFNMAP VMA into A and B and unmap A > > first? It would be broken because we would never free the reservation. > > Likely, there are ways to trigger such a VMA split outside of mremap(). > > As expected ... with a simple reproducer that uses mprotect() to split such > a VMA I can trigger > > x86/PAT: pat_mremap:26448 freeing invalid memtype [mem > 0x00000000-0x00000fff] Wow. Might be worth adding a self test for this if not too difficult, even if as a skipped one w/comment just so we have it ready to go? > > > -- > Cheers, > > David / dhildenb >