From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yu-cheng Yu Subject: Re: [PATCH 00/10] Control Flow Enforcement - Part (3) Date: Tue, 12 Jun 2018 09:21:29 -0700 Message-ID: <1528820489.9324.14.camel@2b52.sc.intel.com> References: <20180607143807.3611-1-yu-cheng.yu@intel.com> <1528815820.8271.16.camel@2b52.sc.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Andy Lutomirski Cc: bsingharora@gmail.com, LKML , linux-doc@vger.kernel.org, Linux-MM , linux-arch , X86 ML , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , "H. J. Lu" , "Shanbhogue, Vedvyas" , "Ravi V. Shankar" , Dave Hansen , Jonathan Corbet , Oleg Nesterov , Arnd Bergmann , mike.kravetz@oracle.com List-Id: linux-arch.vger.kernel.org On Tue, 2018-06-12 at 09:00 -0700, Andy Lutomirski wrote: > On Tue, Jun 12, 2018 at 8:06 AM Yu-cheng Yu wrote: > > > > On Tue, 2018-06-12 at 20:56 +1000, Balbir Singh wrote: > > > > > > On 08/06/18 00:37, Yu-cheng Yu wrote: > > > > This series introduces CET - Shadow stack > > > > > > > > At the high level, shadow stack is: > > > > > > > > Allocated from a task's address space with vm_flags VM_SHSTK; > > > > Its PTEs must be read-only and dirty; > > > > Fixed sized, but the default size can be changed by sys admin. > > > > > > > > For a forked child, the shadow stack is duplicated when the next > > > > shadow stack access takes place. > > > > > > > > For a pthread child, a new shadow stack is allocated. > > > > > > > > The signal handler uses the same shadow stack as the main program. > > > > > > > > > > Even with sigaltstack()? > > > > > > > > > Balbir Singh. > > > > Yes. > > > > I think we're going to need some provision to add an alternate signal > stack to handle the case where the shadow stack overflows. The shadow stack stores only return addresses; its consumption will not exceed a percentage of (program stack size + sigaltstack size) before those overflow. When that happens, there is usually very little we can do. So we set a default shadow stack size that supports certain nested calls and allow sys admin to adjust it. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga09.intel.com ([134.134.136.24]:50792 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933363AbeFLQYi (ORCPT ); Tue, 12 Jun 2018 12:24:38 -0400 Message-ID: <1528820489.9324.14.camel@2b52.sc.intel.com> Subject: Re: [PATCH 00/10] Control Flow Enforcement - Part (3) From: Yu-cheng Yu Date: Tue, 12 Jun 2018 09:21:29 -0700 In-Reply-To: References: <20180607143807.3611-1-yu-cheng.yu@intel.com> <1528815820.8271.16.camel@2b52.sc.intel.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Andy Lutomirski Cc: bsingharora@gmail.com, LKML , linux-doc@vger.kernel.org, Linux-MM , linux-arch , X86 ML , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , "H. J. Lu" , "Shanbhogue, Vedvyas" , "Ravi V. Shankar" , Dave Hansen , Jonathan Corbet , Oleg Nesterov , Arnd Bergmann , mike.kravetz@oracle.com Message-ID: <20180612162129.5ak127eKTGqONYT2rD6WZ28KHqVhlypuEbV3rEUKD8E@z> On Tue, 2018-06-12 at 09:00 -0700, Andy Lutomirski wrote: > On Tue, Jun 12, 2018 at 8:06 AM Yu-cheng Yu wrote: > > > > On Tue, 2018-06-12 at 20:56 +1000, Balbir Singh wrote: > > > > > > On 08/06/18 00:37, Yu-cheng Yu wrote: > > > > This series introduces CET - Shadow stack > > > > > > > > At the high level, shadow stack is: > > > > > > > > Allocated from a task's address space with vm_flags VM_SHSTK; > > > > Its PTEs must be read-only and dirty; > > > > Fixed sized, but the default size can be changed by sys admin. > > > > > > > > For a forked child, the shadow stack is duplicated when the next > > > > shadow stack access takes place. > > > > > > > > For a pthread child, a new shadow stack is allocated. > > > > > > > > The signal handler uses the same shadow stack as the main program. > > > > > > > > > > Even with sigaltstack()? > > > > > > > > > Balbir Singh. > > > > Yes. > > > > I think we're going to need some provision to add an alternate signal > stack to handle the case where the shadow stack overflows. The shadow stack stores only return addresses; its consumption will not exceed a percentage of (program stack size + sigaltstack size) before those overflow. When that happens, there is usually very little we can do. So we set a default shadow stack size that supports certain nested calls and allow sys admin to adjust it.