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=-5.4 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=unavailable 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 6383DC04A6B for ; Mon, 6 May 2019 17:12:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3588B214AE for ; Mon, 6 May 2019 17:12:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727071AbfEFRMc (ORCPT ); Mon, 6 May 2019 13:12:32 -0400 Received: from smtp1.de.adit-jv.com ([93.241.18.167]:57457 "EHLO smtp1.de.adit-jv.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726462AbfEFRMb (ORCPT ); Mon, 6 May 2019 13:12:31 -0400 Received: from localhost (smtp1.de.adit-jv.com [127.0.0.1]) by smtp1.de.adit-jv.com (Postfix) with ESMTP id 843383C00C6; Mon, 6 May 2019 19:12:27 +0200 (CEST) Received: from smtp1.de.adit-jv.com ([127.0.0.1]) by localhost (smtp1.de.adit-jv.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id tK9ZBC8iMECS; Mon, 6 May 2019 19:12:19 +0200 (CEST) Received: from HI2EXCH01.adit-jv.com (hi2exch01.adit-jv.com [10.72.92.24]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by smtp1.de.adit-jv.com (Postfix) with ESMTPS id 863563C004C; Mon, 6 May 2019 19:12:19 +0200 (CEST) Received: from vmlxhi-102.adit-jv.com (10.72.93.184) by HI2EXCH01.adit-jv.com (10.72.92.24) with Microsoft SMTP Server (TLS) id 14.3.439.0; Mon, 6 May 2019 19:12:19 +0200 Date: Mon, 6 May 2019 19:12:16 +0200 From: Eugeniu Rosca To: Geert Uytterhoeven , Simon Horman CC: Simon Horman , Eugeniu Rosca , Geert Uytterhoeven , Chris Brandt , Wolfram Sang , Ulrich Hecht , Greg Kroah-Hartman , "George G . Davis" , Andy Lowe , Linux-Renesas , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Linux Kernel Mailing List , Magnus Damm , Rob Herring , Mark Rutland , Christophe Leroy , Helge Deller , Michael Neuling , Kuninori Morimoto , Philip Yang , Matthew Wilcox , Borislav Petkov , "Darrick J. Wong" , Eugeniu Rosca Subject: Re: [PATCH 1/6] serial: sh-sci: Reveal ptrval in dev_dbg Message-ID: <20190506171216.GA2181@vmlxhi-102.adit-jv.com> References: <20190504004258.23574-1-erosca@de.adit-jv.com> <20190504004258.23574-2-erosca@de.adit-jv.com> <20190506134700.ya565idfzzc3enbm@verge.net.au> <20190506152433.GA22769@vmlxhi-102.adit-jv.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Originating-IP: [10.72.93.184] Sender: linux-renesas-soc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-renesas-soc@vger.kernel.org On Mon, May 06, 2019 at 06:46:57PM +0200, Geert Uytterhoeven wrote: > Hi Eugeniu, > > On Mon, May 6, 2019 at 5:24 PM Eugeniu Rosca wrote: > > On Mon, May 06, 2019 at 03:47:05PM +0200, Simon Horman wrote: > > > On Sat, May 04, 2019 at 02:42:53AM +0200, Eugeniu Rosca wrote: > > > > Starting with v4.15-rc2 commit ad67b74d2469d9 ("printk: hash addresses > > > > printed with %p"), enabling debug prints in sh-sci.c would generate > > > > output like below confusing the users who try to sneak into the > > > > internals of the driver: > > > > > > > > sh-sci e6e88000.serial: sci_request_dma: TX: got channel (____ptrval____) > > > > sh-sci e6e88000.serial: sci_request_dma: mapped 4096@(____ptrval____) to 0x00000006798bf000 > > > > sh-sci e6e88000.serial: sci_request_dma: RX: got channel (____ptrval____) > > > > sh-sci e6e88000.serial: sci_dma_tx_work_fn: (____ptrval____): 0...2, cookie 2 > > > > > > > > There are two possible fixes for that: > > > > - get rid of '%p' prints if they don't reveal any useful information > > > > - s/%p/%px/, since it is unlikely we have any concerns leaking the > > > > pointer values when running a debug/non-production kernel > > > > > > I am concerned that this may expose information in circumstances > > > where it is undesirable. Is it generally accepted practice to > > > use %px in conjunction with dev_dbg() ? > > > > > > ... > > > > Below commits performed a similar s/%p/%px/ update in debug context: > > > > Authors (CC-ed) Commit Subject > > ---------------------------------------- > > Christophe Leroy b18f0ae92b0a1d ("powerpc/prom: fix early DEBUG messages") > > Helge Deller 3847dab7742186 ("parisc: Add alternative coding infrastructure") > > Michael Neuling 51c3c62b58b357 ("powerpc: Avoid code patching freed init sections") > > Kuninori Morimoto dabdbe3ae0cb9a ("ASoC: rsnd: don't use %p for dev_dbg()") > > Philip Yang fa7e65147e5dca ("drm/amdkfd: use %px to print user space address instead of %p") > > Matthew Wilcox 68c1f08203f2b0 ("lib/list_debug.c: print unmangled addresses") > > Borislav Petkov 0e6c16c652cada ("x86/alternative: Print unadorned pointers") > > Darrick J. Wong c96900435fa9fd ("xfs: use %px for data pointers when debugging") > > Helge Deller 04903c06b4854d ("parisc: Show unhashed HPA of Dino chip") > > > > To quote Matthew, with respect to any debug prints: > > If an attacker can force this message to be printed, we've already lost. > > I think the issue with using %px in debug code is that a distro may enable > CONFIG_DYNAMIC_DEBUG (it is enabled in several defconfigs), after which > an attacker just has to convince/trick the system into enabling debug for that > particular driver. How about going the route of commit c96900435fa9fd ("xfs: use %px for data pointers when debugging"), i.e. s/%p/"PTR_FMT"/ like below (this would enable the expected debug output only on manually defining DEBUG in the *.c file, while still keeping the output hashed on DYNAMIC_DEBUG=y if DEBUG is undefined). diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c index 3cd139752d3f..69cd87c5ef0c 100644 --- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -56,6 +56,12 @@ #include #endif +#ifdef DEBUG +#define PTR_FMT "%px" +#else +#define PTR_FMT "%p" +#endif + #include "serial_mctrl_gpio.h" #include "sh-sci.h" @@ -1434,7 +1440,7 @@ static void sci_dma_tx_work_fn(struct work_struct *work) goto switch_to_pio; } - dev_dbg(port->dev, "%s: %p: %d...%d, cookie %d\n", + dev_dbg(port->dev, "%s: "PTR_FMT": %d...%d, cookie %d\n", __func__, xmit->buf, xmit->tail, xmit->head, s->cookie_tx); dma_async_issue_pending(chan); > > > In any case, I won't be affected much if the change is not accepted, > > since it doesn't resolve any major issue on my end. Thanks! > > OK. > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds -- Best Regards, Eugeniu.