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mm: Force TLB flush for PFNMAP mappings before unlink_file_vma()

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commit b67fbebd4c upstream.

Some drivers rely on having all VMAs through which a PFN might be
accessible listed in the rmap for correctness.
However, on X86, it was possible for a VMA with stale TLB entries
to not be listed in the rmap.

This was fixed in mainline with
commit b67fbebd4c ("mmu_gather: Force tlb-flush VM_PFNMAP vmas"),
but that commit relies on preceding refactoring in
commit 18ba064e42 ("mmu_gather: Let there be one tlb_{start,end}_vma()
implementation") and commit 1e9fdf21a4 ("mmu_gather: Remove per arch
tlb_{start,end}_vma()").

This patch provides equivalent protection without needing that
refactoring, by forcing a TLB flush between removing PTEs in
unmap_vmas() and the call to unlink_file_vma() in free_pgtables().

[This is a stable-specific rewrite of the upstream commit!]
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jann Horn 2022-08-31 21:13:48 +02:00 committed by Greg Kroah-Hartman
parent 1ded0ef241
commit 3ffb97fce2
1 changed files with 12 additions and 0 deletions
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12
mm/mmap.c
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@ -2643,6 +2643,18 @@ static void unmap_region(struct mm_struct *mm,
tlb_gather_mmu(&tlb, mm);
update_hiwater_rss(mm);
unmap_vmas(&tlb, vma, start, end);
/*
* Ensure we have no stale TLB entries by the time this mapping is
* removed from the rmap.
* Note that we don't have to worry about nested flushes here because
* we're holding the mm semaphore for removing the mapping - so any
* concurrent flush in this region has to be coming through the rmap,
* and we synchronize against that using the rmap lock.
*/
if ((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) != 0)
tlb_flush_mmu(&tlb);
free_pgtables(&tlb, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
next ? next->vm_start : USER_PGTABLES_CEILING);
tlb_finish_mmu(&tlb);