From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Hansen Subject: Re: [RFC PATCH v2 14/27] mm: Handle THP/HugeTLB shadow stack page fault Date: Fri, 20 Jul 2018 07:20:25 -0700 Message-ID: References: <20180710222639.8241-1-yu-cheng.yu@intel.com> <20180710222639.8241-15-yu-cheng.yu@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20180710222639.8241-15-yu-cheng.yu@intel.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Yu-cheng Yu , x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra List-Id: linux-arch.vger.kernel.org On 07/10/2018 03:26 PM, Yu-cheng Yu wrote: > @@ -1193,6 +1195,8 @@ static int do_huge_pmd_wp_page_fallback(struct vm_fault *vmf, pmd_t orig_pmd, > pte_t entry; > entry = mk_pte(pages[i], vma->vm_page_prot); > entry = maybe_mkwrite(pte_mkdirty(entry), vma); > + if (is_shstk_mapping(vma->vm_flags)) > + entry = pte_mkdirty_shstk(entry); Peter Z was pointing out that we should get rid of all this generic code manipulation. We might not easily be able to do it *all*, but we can do better than what we've got here. Basically, if you have code outside of arch/x86 in your patch set that refers to shadow stacks, you should consider it a bug (for now), especially if you have to hack .c files. For instance, in the code above, you could move the is_shstk_mapping() into: static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma) { if (likely(vma->vm_flags & VM_WRITE)) pte = pte_mkwrite(pte); + pte = arch_pte_mkwrite(pte, vma); + return pte; } ... and add an arch callback that does: static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma) { if (!is_shstk_mapping(vma->vm_flags)) return pte; WARN_ON(... pte bits incompatible with shadow stacks?); /* Lots of comments of course */ entry = pte_mkdirty_shstk(entry); } This is just one example. You are probably going to need a couple of similar things. Just remember: the bar is very high to make changes to .c files outside of arch/x86. You can do a _bit_ more in non-x86 headers, but you have the most freedom to patch what you want as long as it's in arch/x86. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga17.intel.com ([192.55.52.151]:14685 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731305AbeGTPJI (ORCPT ); Fri, 20 Jul 2018 11:09:08 -0400 Subject: Re: [RFC PATCH v2 14/27] mm: Handle THP/HugeTLB shadow stack page fault References: <20180710222639.8241-1-yu-cheng.yu@intel.com> <20180710222639.8241-15-yu-cheng.yu@intel.com> From: Dave Hansen Message-ID: Date: Fri, 20 Jul 2018 07:20:25 -0700 MIME-Version: 1.0 In-Reply-To: <20180710222639.8241-15-yu-cheng.yu@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Yu-cheng Yu , x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , "Ravi V. Shankar" , Vedvyas Shanbhogue Message-ID: <20180720142025.gzxV360DCDPuwSvVBtbnqAzn8NcjKxEEI7WyyaOKIas@z> On 07/10/2018 03:26 PM, Yu-cheng Yu wrote: > @@ -1193,6 +1195,8 @@ static int do_huge_pmd_wp_page_fallback(struct vm_fault *vmf, pmd_t orig_pmd, > pte_t entry; > entry = mk_pte(pages[i], vma->vm_page_prot); > entry = maybe_mkwrite(pte_mkdirty(entry), vma); > + if (is_shstk_mapping(vma->vm_flags)) > + entry = pte_mkdirty_shstk(entry); Peter Z was pointing out that we should get rid of all this generic code manipulation. We might not easily be able to do it *all*, but we can do better than what we've got here. Basically, if you have code outside of arch/x86 in your patch set that refers to shadow stacks, you should consider it a bug (for now), especially if you have to hack .c files. For instance, in the code above, you could move the is_shstk_mapping() into: static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma) { if (likely(vma->vm_flags & VM_WRITE)) pte = pte_mkwrite(pte); + pte = arch_pte_mkwrite(pte, vma); + return pte; } ... and add an arch callback that does: static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma) { if (!is_shstk_mapping(vma->vm_flags)) return pte; WARN_ON(... pte bits incompatible with shadow stacks?); /* Lots of comments of course */ entry = pte_mkdirty_shstk(entry); } This is just one example. You are probably going to need a couple of similar things. Just remember: the bar is very high to make changes to .c files outside of arch/x86. You can do a _bit_ more in non-x86 headers, but you have the most freedom to patch what you want as long as it's in arch/x86.