On Mon, May 13, 2019 at 02:32:43PM -0700, Kees Cook wrote: > On Sat, May 11, 2019 at 09:11:42PM -0700, Matthew Wilcox wrote: > > On Sat, May 11, 2019 at 05:03:08PM -0700, Kees Cook wrote: > > > On Fri, May 10, 2019 at 08:41:43PM -0400, Laura Abbott wrote: > > > > On 5/10/19 3:43 PM, Kees Cook wrote: > > > > > This feature continues to cause more problems than it solves[1]. Its > > > > > intention was to check the bounds of page-allocator allocations by > > > > > using > > > > > __GFP_COMP, for which we would need to find all missing __GFP_COMP > > > > > markings. This work has been on hold and there is an argument[2] > > > > > that such markings are not even the correct signal for checking for > > > > > same-allocation pages. Instead of depending on BROKEN, this just > > > > > removes > > > > > it entirely. It can be trivially reverted if/when a better solution > > > > > for > > > > > tracking page allocator sizes is found. > > > > > > > > > > [1] > > > > > https://www.mail-archive.com/[email protected]/msg37479.html > > > > > [2] > > > > > https://lkml.kernel.org/r/[email protected] > > > > > > > > I agree the page spanning is broken but is it worth keeping the > > > > checks against __rodata __bss etc.? > > > > > > They're all just white-listing later checks (except RODATA which is > > > doing a cheap RO test which is redundant on any architecture with actual > > > rodata...) so they don't have any value in staying without the rest of > > > the page allocator logic. > > > > > > > > - /* Is the object wholly within one base page? */ > > > > > - if (likely(((unsigned long)ptr & (unsigned long)PAGE_MASK) == > > > > > - ((unsigned long)end & (unsigned long)PAGE_MASK))) > > > > > - return; > > > > > - > > > > > - /* Allow if fully inside the same compound (__GFP_COMP) page. */ > > > > > - endpage = virt_to_head_page(end); > > > > > - if (likely(endpage == page)) > > > > > - return; > > > > > > We _could_ keep the mixed CMA/reserved/neither check if we really wanted > > > to, but that's such a corner case of a corner case, I'm not sure it's > > > worth doing the virt_to_head_page() across the whole span to figure > > > it out. > > > > I'd delete that first check, because it's a subset of the second check, > > It seemed easier to short-circuit with a math test before doing the slightly > more expensive virt_to_head_page(end) call. Do you think that's sensible? > > > > > /* Is the object wholly within a single (base or compound) page? */ > > endpage = virt_to_head_page(end); > > if (likely(endpage == page)) > > return; > > > > /* > > * If the start and end are more than MAX_ORDER apart, they must > > * be from separate allocations > > */ > > if (n >= (PAGE_SIZE << MAX_ORDER)) > > usercopy_abort("spans too many pages", NULL, to_user, 0, n); > > > > /* > > * If neither page is compound, we can't tell if the object is > > * within a single allocation or not > > */ > > if (!PageCompound(page) && !PageCompound(endpage)) > > return; > > > > > I really wish we had size of allocation reliably held somewhere. We'll > > > need it for doing memory tagging of the page allocator too... > > > > I think we'll need to store those allocations in a separate data structure > > on the side. As far as the rest of the kernel is concerned, those struct > > pages belong to them once the page allocator has given them. > > Okay, let me work up a page-type refactoring while allocation size can > stay back-burnered. > > -- > Kees Cook
Any progress on this patch? - Eric
