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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, T_DKIMWL_WL_HIGH,URIBL_BLOCKED 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 19946C46460 for ; Thu, 9 Aug 2018 23:03:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C3B7920C01 for ; Thu, 9 Aug 2018 23:03:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="cIMENDdA" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C3B7920C01 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=chromium.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727505AbeHJBaX (ORCPT ); Thu, 9 Aug 2018 21:30:23 -0400 Received: from mail-pl0-f68.google.com ([209.85.160.68]:40191 "EHLO mail-pl0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726756AbeHJBaW (ORCPT ); Thu, 9 Aug 2018 21:30:22 -0400 Received: by mail-pl0-f68.google.com with SMTP id s17-v6so3165451plp.7 for ; Thu, 09 Aug 2018 16:03:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=mime-version:content-transfer-encoding:to:from:in-reply-to:cc :references:message-id:user-agent:subject:date; bh=7qHkOxVlVyaGLDdR6zs2X8MRVLljmE/NXWuhsozuKV4=; b=cIMENDdAIES0knWIOW8JvUVYlVVfDbRL+WI+Jtxw3aOz4UsaU1K2U68jGtwfxsbg3u viwEY4qRnxVQyfKQ4tTlSgJ/N2f3ComlqwoYbHjPuiRlZV91ROWWBlC8p9aMw0I5hzBC 9h8NJVPfgpRHRJUnsRWdaBsVGIw2Qz5IdbbL8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:content-transfer-encoding:to:from :in-reply-to:cc:references:message-id:user-agent:subject:date; bh=7qHkOxVlVyaGLDdR6zs2X8MRVLljmE/NXWuhsozuKV4=; b=nHxH7ExbO97HwMFvMkka0iZIvm9uxUHRswRiNgxP01uQNjWoeMwkaAlOw950rBSpWU uVZPtyeX+jxxcQV7REBn9JF9oWW6f8TlIZFnFpWvwPtDKSJNiEnS6Kb4FZnmpZH2ZHtO +js0jPHyCk8ka+9Hsl0qaSCScc+9cXpNAqBu19t5mI0vGewHT4HUqwDi22g5a2xtoXE6 dWyQlGEJBpW8F8zD5j9p01saGJN4eEEoHLU9UNEPZ8dG+sXH6yfRank6NyW9wf8OeKSV dUeDHwMN6ijF6dGI7SqgxegSsNABARMZjvmkB2pBOY0lrFEcdstkA+o0/o+gF0ckBCxb ym4Q== X-Gm-Message-State: AOUpUlEF+I82DMdQS5aC8jc0wwqi3bZ1181sCZQdE2xmdSLDetoNxg1A ZtCHmvuYCPQRNT1OeV7LHNvv9Q== X-Google-Smtp-Source: AA+uWPyxdGnedLp2YeS53CAnmqzhpEhBFafh4hAuAWzPSPOXux8YYtseWOjmbMu3EEvd8u9TimC5Ng== X-Received: by 2002:a17:902:e85:: with SMTP id 5-v6mr3669498plx.73.1533855799965; Thu, 09 Aug 2018 16:03:19 -0700 (PDT) Received: from localhost ([2620:15c:202:201:7e28:b9f3:6afc:5326]) by smtp.gmail.com with ESMTPSA id 16-v6sm12422038pfp.6.2018.08.09.16.03.19 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 09 Aug 2018 16:03:19 -0700 (PDT) Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable To: Julius Werner From: Stephen Boyd In-Reply-To: Cc: Greg Kroah-Hartman , LKML , Wei-Ning Huang , Julius Werner , Brian Norris , samuel@sholland.org References: <20180809171722.144325-1-swboyd@chromium.org> <20180809171722.144325-8-swboyd@chromium.org> Message-ID: <153385579866.220756.16086660810932774163@swboyd.mtv.corp.google.com> User-Agent: alot/0.7 Subject: Re: [PATCH v3 7/7] firmware: coreboot: Request table region for exclusive access Date: Thu, 09 Aug 2018 16:03:18 -0700 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Archived-At: List-Archive: List-Post: Quoting Julius Werner (2018-08-09 14:07:31) > On Thu, Aug 9, 2018 at 10:17 AM Stephen Boyd wrote: > > > > Call request_mem_region() on the entire coreboot table to make sure > > other devices don't attempt to map the coreboot table in their drivers. > > If drivers need that support, it would be better to provide bus APIs > > they can use to do that through the mapping created in this file. > > > = > Does this prevent userspace from mapping this region via /dev/mem? If > so, let's please not do it to not break compatibility with existing > tools. No it doesn't break. I can still read the memory here with /dev/mem (and cbmem). But that seems to be because of a couple reasons. First, I have CONFIG_STRICT_DEVMEM=3Dy but CONFIG_IO_STRICT_DEVMEM=3Dn. This allows me to map memory that isn't system ram. If CONFIG_IO_STRICT_DEVMEM=3Dy then mapping this I/O region through /dev/mem here would be denied . Furthermore, I see that my system RAM excludes this coreboot table so it doesn't fall into the bucket that CONFIG_STRICT_DEVMEM would find. > (I guess an alternative would be to rewrite 'cbmem' to use > /sys/bus/coreboot/devices if available to get its coreboot table > information. But we'd still need to maintain the old path for > backwards compatibility anyway, so that would really just make it more > complicated.) This sounds like a good idea. Userspace reaching into /dev/mem is not good from a kernel hardening perspective. That's why those strict devmem configs exist. Can cbmem be updated to query information from device drivers instead, so that we can enable CONFIG_IO_STRICT_DEVMEM as well?