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 X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ED671C3F2D2 for ; Mon, 2 Mar 2020 09:37:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C9CA62469C for ; Mon, 2 Mar 2020 09:37:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727465AbgCBJhZ (ORCPT ); Mon, 2 Mar 2020 04:37:25 -0500 Received: from szxga06-in.huawei.com ([45.249.212.32]:43504 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726674AbgCBJhZ (ORCPT ); Mon, 2 Mar 2020 04:37:25 -0500 Received: from DGGEMS406-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id E5EA9B8A6EB8FF894F17; Mon, 2 Mar 2020 17:37:21 +0800 (CST) Received: from [127.0.0.1] (10.173.221.195) by DGGEMS406-HUB.china.huawei.com (10.3.19.206) with Microsoft SMTP Server id 14.3.439.0; Mon, 2 Mar 2020 17:37:11 +0800 Subject: Re: [PATCH v3 0/6] implement KASLR for powerpc/fsl_booke/64 To: Scott Wood , Daniel Axtens , , , , , , , , , , CC: , References: <20200206025825.22934-1-yanaijie@huawei.com> <87tv3drf79.fsf@dja-thinkpad.axtens.net> <8171d326-5138-4f5c-cff6-ad3ee606f0c2@huawei.com> <4c0e7fec63dbc7b91fa6c24692c73c256c131f51.camel@buserror.net> <188971ed-f1c4-39b3-c07e-89cc593d88d7@huawei.com> <530c49dfd97c811dc53ffc78c594d7133f7eb1e9.camel@buserror.net> <35e6c660-3896-bdb8-45f3-c1504aa2171f@huawei.com> <31b5966ba579ef246176a7d8ad18c2c02788dd27.camel@buserror.net> <17658c2b-9eb8-cee9-e9a2-93d316a401b1@huawei.com> <7f608c18250c509ff091990d4bb460846fae11a0.camel@buserror.net> From: Jason Yan Message-ID: <9b1d1d42-ecc9-8d0d-b616-849b0b368d67@huawei.com> Date: Mon, 2 Mar 2020 17:37:09 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.4.2 MIME-Version: 1.0 In-Reply-To: <7f608c18250c509ff091990d4bb460846fae11a0.camel@buserror.net> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.173.221.195] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2020/3/2 16:47, Scott Wood 写道: > On Mon, 2020-03-02 at 15:12 +0800, Jason Yan wrote: >> >> 在 2020/3/2 11:24, Scott Wood 写道: >>> On Mon, 2020-03-02 at 10:17 +0800, Jason Yan wrote: >>>> >>>> 在 2020/3/1 6:54, Scott Wood 写道: >>>>> On Sat, 2020-02-29 at 15:27 +0800, Jason Yan wrote: >>>>>> >>>>>> Turnning to %p may not be a good idea in this situation. So >>>>>> for the REG logs printed when dumping stack, we can disable it when >>>>>> KASLR is open. For the REG logs in other places like show_regs(), >>>>>> only >>>>>> privileged can trigger it, and they are not combind with a symbol, >>>>>> so >>>>>> I think it's ok to keep them. >>>>>> >>>>>> diff --git a/arch/powerpc/kernel/process.c >>>>>> b/arch/powerpc/kernel/process.c >>>>>> index fad50db9dcf2..659c51f0739a 100644 >>>>>> --- a/arch/powerpc/kernel/process.c >>>>>> +++ b/arch/powerpc/kernel/process.c >>>>>> @@ -2068,7 +2068,10 @@ void show_stack(struct task_struct *tsk, >>>>>> unsigned >>>>>> long *stack) >>>>>> newsp = stack[0]; >>>>>> ip = stack[STACK_FRAME_LR_SAVE]; >>>>>> if (!firstframe || ip != lr) { >>>>>> - printk("["REG"] ["REG"] %pS", sp, ip, (void >>>>>> *)ip); >>>>>> + if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) >>>>>> + printk("%pS", (void *)ip); >>>>>> + else >>>>>> + printk("["REG"] ["REG"] %pS", sp, >>>>>> ip, >>>>>> (void *)ip); >>>>> >>>>> This doesn't deal with "nokaslr" on the kernel command line. It also >>>>> doesn't >>>>> seem like something that every callsite should have to opencode, >>>>> versus >>>>> having >>>>> an appropriate format specifier behaves as I described above (and I >>>>> still >>>>> don't see why that format specifier should not be "%p"). >>>>> >>>> >>>> Actually I still do not understand why we should print the raw value >>>> here. When KALLSYMS is enabled we have symbol name and offset like >>>> put_cred_rcu+0x108/0x110, and when KALLSYMS is disabled we have the raw >>>> address. >>> >>> I'm more concerned about the stack address for wading through a raw stack >>> dump >>> (to find function call arguments, etc). The return address does help >>> confirm >>> that I'm on the right stack frame though, and also makes looking up a line >>> number slightly easier than having to look up a symbol address and then >>> add >>> the offset (at least for non-module addresses). >>> >>> As a random aside, the mismatch between Linux printing a hex offset and >>> GDB >>> using decimal in disassembly is annoying... >>> >> >> OK, I will send a RFC patch to add a new format specifier such as "%pk" >> or change the exsiting "%pK" to print raw value of addresses when KASLR >> is disabled and print hash value of addresses when KASLR is enabled. >> Let's see what the printk guys would say :) > > I'm not sure that a new format specifier is needed versus changing the > behavior of "%p", and "%pK" definitely doesn't seem suitable given that it's > intended to be more restricted than "%p" (see commit ef0010a30935de4). The > question is whether there is a legitimate reason to hash in the absence of > kaslr. > The problem is that if we change the behavior of "%p", we have to turn all exsiting "%p" to "%pK". Hashing is still reasonable when there is no kaslr because some architectures support randomize at build time such as arm64. > -Scott > > > > . >