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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Stat-Signature: 5sdyurinxx61dcrouoff7ajr8k8kxnue X-Rspam-User: X-Rspamd-Queue-Id: 679E020004 X-HE-Tag: 1760592902-996259 X-HE-Meta: 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 jjcawvUY qXDyuNydi4Qf4zJ2WwFN5+fjjvfW6CNTlP4fMYsonOHvSCNfG/tk6iQCe/1vYdlv3+NLpDqtV+T8UhASgDUGL2Ysl3OVxryJ1s4iyJ2hUlMCWmTdc/kw7cknZ3G2KurD3kRtY+Sim5rXIwgFMooevk1E2E9YuAjy/dcKebMD+x9HctOEe5jaFHKazoz/gnCu2rtszwxdBj7GCRM+TiRNWWdYm6w== 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 > --- Thanks, I missed this. > 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)) There should be no chance that we end up with a pteval which is not none *and* not present, if you look at the callers of release_pte_pages. So perhaps we should keep this either the same, or, after "if(pte_none(pteval))", do a WARN_ON_ONCE(!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)) { > /* > * 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 ||