On Fri, Feb 24, 2023 at 7:16 AM Peter Collingbourne pcc@google.com wrote:

This reverts commit 487a32ec24be819e747af8c2ab0d5c515508086a.

The should_skip_kasan_poison() function reads the PG_skip_kasan_poison flag from page->flags. However, this line of code in free_pages_prepare():

page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;

clears most of page->flags, including PG_skip_kasan_poison, before calling should_skip_kasan_poison(), which meant that it would never return true as a result of the page flag being set. Therefore, fix the code to call should_skip_kasan_poison() before clearing the flags, as we were doing before the reverted patch.

Signed-off-by: Peter Collingbourne pcc@google.com Fixes: 487a32ec24be ("kasan: drop skip_kasan_poison variable in free_pages_prepare") Cc: stable@vger.kernel.org # 6.1 Link: https://linux-review.googlesource.com/id/Ic4f13affeebd20548758438bb9ed9ca40e...

---

mm/page_alloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c index ac1fc986af44..7136c36c5d01 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1398,6 +1398,7 @@ static __always_inline bool free_pages_prepare(struct page *page, unsigned int order, bool check_free, fpi_t fpi_flags) { int bad = 0;

•   bool skip_kasan_poison = should_skip_kasan_poison(page, fpi_flags);
    bool init = want_init_on_free();
  
    VM_BUG_ON_PAGE(PageTail(page), page);
  

@@ -1470,7 +1471,7 @@ static __always_inline bool free_pages_prepare(struct page *page, * With hardware tag-based KASAN, memory tags must be set before the * page becomes unavailable via debug_pagealloc or arch_free_page. */

•   if (!should_skip_kasan_poison(page, fpi_flags)) {
  

•   if (!skip_kasan_poison) {
            kasan_poison_pages(page, order, init);
  
            /* Memory is already initialized if KASAN did it internally. */
  

-- 2.39.2.637.g21b0678d19-goog

Reviewed-by: Andrey Konovalov andreyknvl@gmail.com

Thank you for fixing this, Peter!