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 D3C34C4332F for ; Fri, 4 Mar 2022 14:54:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239993AbiCDOzV (ORCPT ); Fri, 4 Mar 2022 09:55:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46546 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239986AbiCDOzS (ORCPT ); Fri, 4 Mar 2022 09:55:18 -0500 Received: from out30-44.freemail.mail.aliyun.com (out30-44.freemail.mail.aliyun.com [115.124.30.44]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 13C521B0C4E; Fri, 4 Mar 2022 06:54:29 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R231e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04423;MF=ashimida@linux.alibaba.com;NM=1;PH=DS;RN=23;SR=0;TI=SMTPD_---0V6CkHJB_1646405664; Received: from 192.168.193.155(mailfrom:ashimida@linux.alibaba.com fp:SMTPD_---0V6CkHJB_1646405664) by smtp.aliyun-inc.com(127.0.0.1); Fri, 04 Mar 2022 22:54:25 +0800 Message-ID: Date: Fri, 4 Mar 2022 06:54:23 -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 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> From: Dan Li In-Reply-To: <202203031105.A1B4CAE6@keescook> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > 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; }