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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 040E3C433F5 for ; Thu, 7 Apr 2022 23:43:43 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 13A8D6B0072; Thu, 7 Apr 2022 19:43:33 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0EA886B0073; Thu, 7 Apr 2022 19:43:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id ECCB56B0074; Thu, 7 Apr 2022 19:43:32 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.28]) by kanga.kvack.org (Postfix) with ESMTP id DE3546B0072 for ; Thu, 7 Apr 2022 19:43:32 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id A884062AC3 for ; Thu, 7 Apr 2022 23:43:22 +0000 (UTC) X-FDA: 79331711844.16.330379E Received: from mail-pl1-f173.google.com (mail-pl1-f173.google.com [209.85.214.173]) by imf07.hostedemail.com (Postfix) with ESMTP id 100CC40004 for ; Thu, 7 Apr 2022 23:43:21 +0000 (UTC) Received: by mail-pl1-f173.google.com with SMTP id n18so6431230plg.5 for ; Thu, 07 Apr 2022 16:43:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20210112.gappssmtp.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Pj1m7MSDvtJlWRF9Wy+Vpq6RgerTAYzRujcuh4rQzlI=; b=r3TTgu/GSCJO4lgpmKH+62o1l/WHx0lcIaWhYDrBkTHGeIniXcLPe1ymY9DY99QIse m7zuXMNL0ZG33Krt4B/McCxKF1j0bTCNGqCexVynVoEb1NI76yDgA4Y67whCjQJ7IhsF Gzt6DRtqw+NmkbtULcdhF2D7PqxUEZiT2UoNGTlsiSE7C9eWRz/pBh5PuzDVHD7XYYYu 7eNxdPucFOYzKd+IpapxE0VyzB+PEhO9f9fSmx55MxwIEZGHSMiuWFRWZIecxWSsXv9Q GWOf1tYDrjfeyQDxVs7RlOJ4QwYj5ohNY7aK4fhQunFYuXENc+xfFfFBZIUh6kVGesxX zBbw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Pj1m7MSDvtJlWRF9Wy+Vpq6RgerTAYzRujcuh4rQzlI=; b=oeUL7QtvxQNUFW9eEoCej+1+H49n+9RNfA1Y47PPCDzMDitQ78gdXTTXuNeTD1xp0V LzRhW4GD+DFH5W03lZLN1XXsIobYcX6MpX117/nD8Sl2nDeDo//Z0XVt/8GTe6V+T2L4 BvydKJbUozmqOieIsYJMEBM3sVba3XpuTCDZlwmZFAxBykZPSNRnhb6Aax6pAOd2F9tC ZuuJE+JK9LOOfpWaxic5lD/uMl5a0yHJ1hJIRGRaLGaNrZ0z8Ko6B5TZiDWmveqyOa9e DgZVV684Ax929buX9PAe8+J97JwqIZRz566fv6AuktrGrppn0YtCM84uUB6otA5PqO/0 syEQ== X-Gm-Message-State: AOAM531jzh1dhU6TKBBn54kNOyzv8Sp2kkip7g3oXfy7HUmO6bl6cGQB +nXPDNWswbZIm0lrhNRv1byFqmSAoPnTqCq95XP9LQ== X-Google-Smtp-Source: ABdhPJyMwfI9k4IT6Nyps62AlO0jNpMsz9kn3F6fV9YDeY5aDDromm/1G7ZPfCQGxOTNQEl3GgO5lOpz7A1/08m7i24= X-Received: by 2002:a17:903:32c5:b0:156:b466:c8ed with SMTP id i5-20020a17090332c500b00156b466c8edmr16267018plr.34.1649375000969; Thu, 07 Apr 2022 16:43:20 -0700 (PDT) MIME-Version: 1.0 References: <159009507306.847224.8502634072429766747.stgit@dwillia2-desk3.amr.corp.intel.com> <202005211950.D56130B81@keescook> <202204061243.FB134CA4B1@keescook> In-Reply-To: From: Dan Williams Date: Thu, 7 Apr 2022 16:43:10 -0700 Message-ID: Subject: Re: [PATCH v4] /dev/mem: Revoke mappings when a driver claims the region To: Kees Cook Cc: Greg KH , Arnd Bergmann , Ingo Molnar , Matthew Wilcox , Russell King , Andrew Morton , Linux Kernel Mailing List , Linux MM Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: 4poiwkx87qwriidgmbkradak1u7g7o4y Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=intel-com.20210112.gappssmtp.com header.s=20210112 header.b="r3TTgu/G"; spf=none (imf07.hostedemail.com: domain of dan.j.williams@intel.com has no SPF policy when checking 209.85.214.173) smtp.mailfrom=dan.j.williams@intel.com; dmarc=fail reason="No valid SPF, DKIM not aligned (relaxed)" header.from=intel.com (policy=none) X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 100CC40004 X-HE-Tag: 1649375001-666051 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Apr 7, 2022 at 11:47 AM Dan Williams wrote: > > On Wed, Apr 6, 2022 at 12:46 PM Kees Cook wrote: > > > > *thread necromancy* > > It's alive! > > > > > Hi Dan, > > > > I'm doing a KSPP bug scrub and am reviewing > > https://github.com/KSPP/linux/issues/74 again. > > > > Do you have a chance to look at this? I'd love a way to make mmap() > > behave the same way as read() for the first meg of /dev/mem. > > You want 0-reads or SIGBUS when attempting to access the first 1MB? > > Because it sounds like what you want is instead of loudly failing with > -EPERM in drivers/char/mem.c::mmap_mem() you want it to silently > succeed but swap in the zero page, right? Otherwise if it's SIGBUS > then IO_STRICT_DEVMEM=y + marking that span as IORESOURCE_BUSY will > "Do the Right Thing (TM).". In other words, if IO_STRICT_DEVMEM is enabled then the enforcement is already there at least for anything marked IORESOURCE_BUSY. So if tools are ok with that protection today, maybe there is no need to do the zero page dance. I.e. legacy tools the read(2) /dev/mem below 1MB get zeroes, and apparently no tools were mmap'ing below 1MB otherwise they would have complained by now? At least Fedora is shipping IO_STRICT_DEVMEM these days: https://src.fedoraproject.org/rpms/kernel/blob/rawhide/f/kernel-x86_64-fedora.config#_2799