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=-5.3 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 91F6CC3F2CD for ; Mon, 2 Mar 2020 02:17:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 741F424697 for ; Mon, 2 Mar 2020 02:17:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726838AbgCBCRi (ORCPT ); Sun, 1 Mar 2020 21:17:38 -0500 Received: from szxga07-in.huawei.com ([45.249.212.35]:60200 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726695AbgCBCRi (ORCPT ); Sun, 1 Mar 2020 21:17:38 -0500 Received: from DGGEMS406-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 489E9EE228E2F0D26E70; Mon, 2 Mar 2020 10:17:36 +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 10:17:29 +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> From: Jason Yan Message-ID: <35e6c660-3896-bdb8-45f3-c1504aa2171f@huawei.com> Date: Mon, 2 Mar 2020 10:17:28 +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: <530c49dfd97c811dc53ffc78c594d7133f7eb1e9.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 2020/3/1 6:54, Scott Wood 写道: > On Sat, 2020-02-29 at 15:27 +0800, Jason Yan wrote: >> >> 在 2020/2/29 12:28, Scott Wood 写道: >>> On Fri, 2020-02-28 at 14:47 +0800, Jason Yan wrote: >>>> >>>> 在 2020/2/28 13:53, Scott Wood 写道: >>>>> >>>>> I don't see any debug setting for %pK (or %p) to always print the >>>>> actual >>>>> address (closest is kptr_restrict=1 but that only works in certain >>>>> contexts)... from looking at the code it seems it hashes even if kaslr >>>>> is >>>>> entirely disabled? Or am I missing something? >>>>> >>>> >>>> Yes, %pK (or %p) always hashes whether kaslr is disabled or not. So if >>>> we want the real value of the address, we cannot use it. But if you only >>>> want to distinguish if two pointers are the same, it's ok. >>> >>> Am I the only one that finds this a bit crazy? If you want to lock a >>> system >>> down then fine, but why wage war on debugging even when there's no >>> randomization going on? Comparing two pointers for equality is not always >>> adequate. >>> >> >> AFAIK, %p hashing is only exist because of many legacy address printings >> and force who really want the raw values to switch to %px or even %lx. >> It's not the opposite of debugging. Raw address printing is not >> forbidden, only people need to estimate the risk of adrdress leaks. > > Yes, but I don't see any format specifier to switch to that will hash in a > randomized production environment, but not in a debug or other non-randomized > environment which seems like the ideal default for most debug output. > Sorry I have no idea why there is no format specifier considered for switching of randomized or non-randomized environment. May they think that raw address should not leak in non-randomized environment too. May be Kees or Tobin can answer this question. Kees? Tobin? >> >> 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. > -Scott > > > > . >