On Tue, Aug 14, 2018 at 01:02:55PM +0000, Yuanxiaofeng (XiAn) wrote: > 1, When the THREAD_SIZE is less than PAGE_SIZE, the stack will allocate memory by kmem_cache_alloc_node(), it's slab memory and will execute __check_heap_object(). > 2, When CONFIG_HARDENED_USERCOPY_PAGESPAN is enabled, the multiple-pages stacks will do some check in check_page_span(). I understand the checks will still do something useful, but I do not see the scenario in which an object would satisfy the stack checks but fail the heap checks. > So, I set some restrictions to make sure the useful check will not be skipped. > > -----Original Message----- > From: Matthew Wilcox [mailto:willy@xxxxxxxxxxxxx] > Sent: Tuesday, August 14, 2018 8:35 PM > To: Yuanxiaofeng (XiAn) > Cc: keescook@xxxxxxxxxxxx; linux-mm@xxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx > Subject: Re: [PATCH RFC] usercopy: optimize stack check flow when the > > On Tue, Aug 14, 2018 at 08:17:31PM +0800, Xiaofeng Yuan wrote: > > The check_heap_object() checks the spanning multiple pages and slab. > > When the page-spanning test is disabled, the check_heap_object() is > > redundant for spanning multiple pages. However, the kernel stacks are > > multiple pages under certain conditions: CONFIG_ARCH_THREAD_STACK_ALLOCATOR > > is not defined and (THREAD_SIZE >= PAGE_SIZE). At this point, We can skip > > the check_heap_object() for kernel stacks to improve performance. > > Similarly, the virtually-mapped stack can skip check_heap_object() also, > > beacause virt_addr_valid() will return. > > Why not just check_stack_object() first, then check_heap_object() second? >
