kmsan_free_page() is called by the page allocator's free_pages_prepare() during page freeing. It's job is to poison all the memory covered by the page. It can be called with an order-0 page, a compound high-order page or a non-compound high-order page. But page_size() only works for order-0 and compound pages. For a non-compound high-order page it will incorrectly return PAGE_SIZE.

The implication is that the tail pages of a high-order non-compound page do not get poisoned at free, so any invalid access while they are free could go unnoticed. It looks like the pages will be poisoned again at allocaiton time, so that would bookend the window.

Fix this by using the order parameter to calculate the size.

Fixes: b073d7f8aee4 ("mm: kmsan: maintain KMSAN metadata for page operations") Cc: stable@vger.kernel.org Signed-off-by: Ryan Roberts ryan.roberts@arm.com ---

Hi,

I noticed this during code review, so perhaps I've just misunderstood the intent of the code.

I don't have the means to compile and run on x86 with KMSAN enabled though, so punting this out hoping someone might be able to validate/test. I guess there is a small chance this could lead to KMSAN finding some new issues?

Applies against today's mm-unstable (344d3580dacd).

Thanks, Ryan

mm/kmsan/shadow.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c index e7f554a31bb4..9e1c5f2b7a41 100644 --- a/mm/kmsan/shadow.c +++ b/mm/kmsan/shadow.c @@ -207,7 +207,7 @@ void kmsan_free_page(struct page *page, unsigned int order) if (!kmsan_enabled || kmsan_in_runtime()) return; kmsan_enter_runtime(); - kmsan_internal_poison_memory(page_address(page), page_size(page), + kmsan_internal_poison_memory(page_address(page), PAGE_SIZE << order, GFP_KERNEL & ~(__GFP_RECLAIM), KMSAN_POISON_CHECK | KMSAN_POISON_FREE); kmsan_leave_runtime(); -- 2.43.0