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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: 99f4hqyaqxectc5qgw96ifz583ugqihm X-Rspamd-Queue-Id: 94E054000A X-Rspamd-Server: rspam06 X-Rspam-User: X-HE-Tag: 1760595435-239581 X-HE-Meta: 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 9qoU/HAd UhPF/KYcVLMXemJKPONKeJYltFmnIZLUrm0PFim7JW7/wQxWwlNWowLvlBZsC5v/3NQDYLS1AXpo7mLNyyPyYwIlO7dpFqYlnvRPhC0VCuIm+/PdQU37uU8sqY/rw7Kfbj9ULtyKA5S+JfsBXjhHE+TOl90WJxQ1R/RrBNb3kQCFdyi1RNJc6QxjcB52G4HCWTss1JD7acxKgtxyNyfl5/s6X31J6mjBGFELPr4ar3cAd2r1S1h573lLv2mayQOv6Kt1k4x7w0sPIM/0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 16/10/25 9:06 am, Lance Yang wrote: > From: Lance Yang > > A non-present entry, like a swap PTE, contains completely different data > (swap type and offset). pte_pfn() doesn't know this, so if we feed it a > non-present entry, it will spit out a junk PFN. > > What if that junk PFN happens to match the zeropage's PFN by sheer > chance? While really unlikely, this would be really bad if it did. > > So, let's fix this potential bug by ensuring all calls to is_zero_pfn() > in khugepaged.c are properly guarded by a pte_present() check. > > Suggested-by: Lorenzo Stoakes > Signed-off-by: Lance Yang > --- > mm/khugepaged.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index d635d821f611..0341c3d13e9e 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -516,7 +516,7 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte, > pte_t pteval = ptep_get(_pte); > unsigned long pfn; > > - if (pte_none(pteval)) > + if (!pte_present(pteval)) > continue; > pfn = pte_pfn(pteval); > if (is_zero_pfn(pfn)) > @@ -690,9 +690,10 @@ static void __collapse_huge_page_copy_succeeded(pte_t *pte, > address += nr_ptes * PAGE_SIZE) { > nr_ptes = 1; > pteval = ptep_get(_pte); > - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > + if (pte_none(pteval) || > + (pte_present(pteval) && is_zero_pfn(pte_pfn(pteval)))) { > add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); > - if (is_zero_pfn(pte_pfn(pteval))) { > + if (!pte_none(pteval)) { Could save a level of indentation by saying if (pte_none(pteval)) continue; That would make it crystal clear that we do nothing when pte is none, and we do something when pte is pointing to zero pfn. Reviewed-by: Dev Jain > /* > * ptl mostly unnecessary. > */ > @@ -794,7 +795,8 @@ static int __collapse_huge_page_copy(pte_t *pte, struct folio *folio, > unsigned long src_addr = address + i * PAGE_SIZE; > struct page *src_page; > > - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > + if (pte_none(pteval) || > + (pte_present(pteval) && is_zero_pfn(pte_pfn(pteval)))) { > clear_user_highpage(page, src_addr); > continue; > } > @@ -1294,7 +1296,8 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, > goto out_unmap; > } > } > - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { > + if (pte_none(pteval) || > + (pte_present(pteval) && is_zero_pfn(pte_pfn(pteval)))) { > ++none_or_zero; > if (!userfaultfd_armed(vma) && > (!cc->is_khugepaged ||