From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f197.google.com (mail-pg1-f197.google.com [209.85.215.197]) by kanga.kvack.org (Postfix) with ESMTP id AB93D6B0007 for ; Tue, 14 Aug 2018 09:09:30 -0400 (EDT) Received: by mail-pg1-f197.google.com with SMTP id c21-v6so8612329pgw.0 for ; Tue, 14 Aug 2018 06:09:30 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [2607:7c80:54:e::133]) by mx.google.com with ESMTPS id r84-v6si22124707pfj.355.2018.08.14.06.09.29 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 14 Aug 2018 06:09:29 -0700 (PDT) Date: Tue, 14 Aug 2018 06:09:28 -0700 From: Matthew Wilcox Subject: Re: [PATCH RFC] usercopy: optimize stack check flow when the page-spanning test is disabled Message-ID: <20180814130928.GB25328@bombadil.infradead.org> References: <1534249051-56879-1-git-send-email-yuanxiaofeng1@huawei.com> <20180814123454.GA25328@bombadil.infradead.org> <494CFD22286B8448AF161132C5FE9A985B624E05@dggema521-mbx.china.huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <494CFD22286B8448AF161132C5FE9A985B624E05@dggema521-mbx.china.huawei.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Yuanxiaofeng (XiAn)" Cc: "keescook@chromium.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" 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@infradead.org] > Sent: Tuesday, August 14, 2018 8:35 PM > To: Yuanxiaofeng (XiAn) > Cc: keescook@chromium.org; linux-mm@kvack.org; linux-kernel@vger.kernel.org > 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? >