On Tue, Jun 15, 2021 at 10:12:06AM +0200, David Hildenbrand wrote: > On 14.06.21 22:31, Rustam Kovhaev wrote: > > hello Catalin, Andrew! > > > > while troubleshooting a false positive syzbot kmemleak report i have > > noticed an interesting behavior in kmemleak and i wonder whether it is > > behavior by design and should be documented, or maybe something to > > improve. > > Hi, > > See below regarding documentation. > > > apologies if some of the questions do not make sense, i am still going > > through kmemleak code.. > > > > a) kmemleak scans struct page (kmemleak.c:1462), but it does not scan > > the actual contents (page_address(page)) of the page. > > if we allocate an object with kmalloc(), then allocate page with > > alloc_page(), and if we put kmalloc pointer somewhere inside that page, > > kmemleak will report kmalloc pointer as a false positive. > > should we improve kmemleak and make it scan page contents? > > or will this bring too many false negatives? > > I looked into this a while ago to see which parts of the kernel end up > reading random physical page content and was happy to see that kmemleak does > *not* scan random physical memory :) > > We have to be very careful when reading random physical page content, > especially in virt environments this is really undesired, or when dealing > with memory holes, memory with problematic semantics like gart memory ... i see, makes sense, thank you for the info! > > The doc (Documentation/dev-tools/kmemleak.rst) states "Page allocations and > ioremap are not tracked.", which includes the alloc_page() example you gave > I think. i see it now, ty!
