On Thu, Jun 20, 2019 at 04:46:06PM -0400, Qian Cai wrote: > The linux-next commit "mm: security: introduce init_on_alloc=1 and > init_on_free=1 boot options" [1] introduced a false positive when > init_on_free=1 and page_poison=on, due to the page_poison expects the > pattern 0xaa when allocating pages which were overwritten by > init_on_free=1 with 0. > > Fix it by switching the order between kernel_init_free_pages() and > kernel_poison_pages() in free_pages_prepare(). Cool; this seems like the right approach. Alexander, what do you think? Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -Kees > > [1] https://patchwork.kernel.org/patch/10999465/ > > Signed-off-by: Qian Cai <cai@xxxxxx> > --- > > v2: After further debugging, the issue after switching order is likely a > separate issue as clear_page() should not cause issues with future > accesses. > > 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 54dacf35d200..32bbd30c5f85 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1172,9 +1172,10 @@ static __always_inline bool free_pages_prepare(struct page *page, > PAGE_SIZE << order); > } > arch_free_page(page, order); > - kernel_poison_pages(page, 1 << order, 0); > if (want_init_on_free()) > kernel_init_free_pages(page, 1 << order); > + > + kernel_poison_pages(page, 1 << order, 0); > if (debug_pagealloc_enabled()) > kernel_map_pages(page, 1 << order, 0); > > -- > 1.8.3.1 > -- Kees Cook
