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[14.202.194.140]) by smtp.googlemail.com with ESMTPSA id l71-v6sm25500965pge.8.2018.06.19.01.52.32 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 19 Jun 2018 01:52:40 -0700 (PDT) Message-ID: <09b7cc16ee5275d4ef3dffb11942e3f2ba44aedd.camel@gmail.com> Subject: Re: [PATCH 00/10] Control Flow Enforcement - Part (3) From: Balbir Singh To: Andy Lutomirski Cc: Yu-cheng Yu , 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 Date: Tue, 19 Jun 2018 18:52:29 +1000 In-Reply-To: References: <20180607143807.3611-1-yu-cheng.yu@intel.com> <1528815820.8271.16.camel@2b52.sc.intel.com> <814fc15e80908d8630ff665be690ccbe6e69be88.camel@gmail.com> <1528988176.13101.15.camel@2b52.sc.intel.com> <2b77abb17dfaf58b7c23fac9d8603482e1887337.camel@gmail.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.1-2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Mon, 2018-06-18 at 14:44 -0700, Andy Lutomirski wrote: > On Sat, Jun 16, 2018 at 8:16 PM Balbir Singh wrote: > > > > On Thu, 2018-06-14 at 07:56 -0700, Yu-cheng Yu wrote: > > > On Thu, 2018-06-14 at 11:07 +1000, Balbir Singh wrote: > > > > On Tue, 2018-06-12 at 08:03 -0700, 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()? > > > > > > > > > > > > > > > > Yes. > > > > > > > > I am not convinced that it would work, as we switch stacks, oveflow might > > > > be an issue. I also forgot to bring up setcontext(2), I presume those > > > > will get new shadow stacks > > > > > > Do you mean signal stack/sigaltstack overflow or swapcontext in a signal > > > handler? > > > > > > > I meant any combination of that. If there is a user space threads implementation that uses sigaltstack for switching threads > > > > Anyone who does that is nuts. The whole point of user space threads > is speed, and signals are very slow. For userspace threads to work, > we need an API to allocate new shadow stacks, and we need to use the > extremely awkwardly defined RSTORSSP stuff to switch. (I assume this > is possible on an ISA level. The docs are bad, and the mnemonics for > the relevant instructions are nonsensical.) The whole point was to ensure we don't break applications/code that work today. I think as long as there is a shadow stack allocated corresponding to the user space stack and we can Restore SSP as we switch things should be fine. Balbir Singh. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html