From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3275AC433EF for ; Fri, 4 Mar 2022 15:01:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240004AbiCDPCQ (ORCPT ); Fri, 4 Mar 2022 10:02:16 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35476 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229934AbiCDPCO (ORCPT ); Fri, 4 Mar 2022 10:02:14 -0500 Received: from out199-12.us.a.mail.aliyun.com (out199-12.us.a.mail.aliyun.com [47.90.199.12]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 48FCA177D24; Fri, 4 Mar 2022 07:01:25 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R841e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04407;MF=ashimida@linux.alibaba.com;NM=1;PH=DS;RN=23;SR=0;TI=SMTPD_---0V6CkI3R_1646406078; Received: from 192.168.193.155(mailfrom:ashimida@linux.alibaba.com fp:SMTPD_---0V6CkI3R_1646406078) by smtp.aliyun-inc.com(127.0.0.1); Fri, 04 Mar 2022 23:01:19 +0800 Message-ID: <48268e7c-a912-c648-be69-b5e41639bf3e@linux.alibaba.com> Date: Fri, 4 Mar 2022 07:01:18 -0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 Subject: Re: [PATCH v3 2/2] lkdtm: Add Shadow Call Stack tests Content-Language: en-US From: Dan Li To: Kees Cook Cc: akpm@linux-foundation.org, arnd@arndb.de, catalin.marinas@arm.com, gregkh@linuxfoundation.org, linux@roeck-us.net, luc.vanoostenryck@gmail.com, elver@google.com, mark.rutland@arm.com, masahiroy@kernel.org, ojeda@kernel.org, nathan@kernel.org, npiggin@gmail.com, ndesaulniers@google.com, samitolvanen@google.com, shuah@kernel.org, tglx@linutronix.de, will@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, llvm@lists.linux.dev, linux-hardening@vger.kernel.org References: <20220303073340.86008-1-ashimida@linux.alibaba.com> <20220303074339.86337-1-ashimida@linux.alibaba.com> <202203031010.0A492D114@keescook> <202203031105.A1B4CAE6@keescook> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/4/22 06:54, Dan Li wrote: > > > On 3/3/22 11:09, Kees Cook wrote: >> On Thu, Mar 03, 2022 at 10:42:45AM -0800, Kees Cook wrote: >>> Though, having the IS_ENABLED in there makes me wonder if this test >>> should instead be made _survivable_ on failure. Something like this, >>> completely untested: >>> >>> >>> And we should, actually, be able to make the "set_lr" functions be >>> arch-specific, leaving the test itself arch-agnostic.... >> >> Yeah, as a tested example, this works for x86_64, and based on what you >> had, I'd expect it to work on arm64 too: >> >> #include >> >> static __attribute__((noinline)) >> void set_return_addr(unsigned long *expected, unsigned long *addr) >> { >>      /* Use of volatile is to make sure final write isn't seen as a dead store. */ >>      unsigned long * volatile *ret_addr = (unsigned long **)__builtin_frame_address(0) + 1; >> >>      /* Make sure we've found the right place on the stack before writing it. */ >>      if (*ret_addr == expected) >>          *ret_addr = addr; >> } >> >> volatile int force_label; >> int main(void) >> { >>      do { >>          /* Keep labels in scope. */ >>          if (force_label) >>              goto normal; >>          if (force_label) >>              goto redirected; >> >>          set_return_addr(&&normal, &&redirected); >> normal: >>          printf("I should be skipped\n"); >>          break; > > From the assembly code, it seems that "&&normal" does't always equal > to the address of label "normal" when we use clang with -O2. > >> redirected: >>          printf("Redirected\n"); >>      } while (0); >> > > The address of "&&redirected" may appear in the middle of the assembly > instructions of the printf. If we unconditionally jump to "&&normal",> it may crash directly because x0 is not set correctly. Sorry, it should be: The address of "&&redirected" may appear in the middle of the assembly instructions of the printf. If we unconditionally jump to "&&redirected", it may crash directly because x0 of printf is not set correctly. Thanks, Dan. > >>      return 0; >> } >> >> >> It does _not_ work under Clang, though, which I'm still looking at. >> > > AFAICT, maybe we could specify -O0 optimization to bypass this. > > > BTW: > Occasionally found, the following code works correctly, but i think > it doesn't solve the issue :) > > #include > > static __attribute__((noinline)) > void set_return_addr(unsigned long *expected, unsigned long *addr) > { >     /* Use of volatile is to make sure final write isn't seen as a dead store. */ >     unsigned long * volatile *ret_addr = (unsigned long **)__builtin_frame_address(0) + 1; > >     /* Make sure we've found the right place on the stack before writing it. */ > //    if (*ret_addr == expected) >         *ret_addr = addr; > } > volatile int force_label; > int main(void) > { >     do { >         /* Keep labels in scope. */ >         if (force_label) >             goto normal; >         if (force_label) >             goto redirected; > >         set_return_addr(&&normal, &&redirected); > normal: >         printf("I should be skipped\n"); >         break; > > redirected: >         printf("Redirected\n"); >         printf("\n");                //add a new printf >     } while (0); > >     return 0; > }