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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C54BFC61D97 for ; Fri, 27 Jan 2023 16:13:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234641AbjA0QNU (ORCPT ); Fri, 27 Jan 2023 11:13:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40376 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234646AbjA0QNR (ORCPT ); Fri, 27 Jan 2023 11:13:17 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C73AF3E617 for ; Fri, 27 Jan 2023 08:12:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1674835952; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=SwogfK/xLNDHbbwXO1sIym9vY9/jCFhsud5wbKcvQaU=; b=MvkDhpC60BEksuWrQlrG0YhuNwEfwWEQ4Ydn/2F3+tZb9mPK4FJghmtnfhsGbXuJfsOWgM hg1xZsNBJ8tnV1ZCYfFkhPYeAOKovrmysSYrr3FGaIUkH26ghpcwh6UuhF7He1BLTk8X1n RX/y0daxFpnfb8F4OUGWzyvlnGCObKc= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-597-00SKtRSvM7W-i3RH4AwoYA-1; Fri, 27 Jan 2023 11:12:30 -0500 X-MC-Unique: 00SKtRSvM7W-i3RH4AwoYA-1 Received: by mail-wm1-f70.google.com with SMTP id o5-20020a05600c4fc500b003db0b3230efso4898675wmq.9 for ; Fri, 27 Jan 2023 08:12:30 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:in-reply-to:organization:from:references :cc:to:content-language:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=SwogfK/xLNDHbbwXO1sIym9vY9/jCFhsud5wbKcvQaU=; b=7dHpqEVD85DK8SWAe1OQiOTf6yLf0xRbFFh5z/CsphHqYCa5voRbdKysQJg2YjnpS8 ZZVef9V9goB0lkRJvKXUJMCigXSGWnXGY+ofjgXHY3nnPpgnIYBoGLwNdFXI4Dkvi4fU bsebGq6da1C0LwCVIdOQOE8OYAIV2471NozhnhfCaak1myW3AIhCBQbsT/S31fQNM2wA xMNZ9U4L7dQ4jZQbZ1KTA+qG7747yxfl//tokYWq2NYRjauTgdsTrtBpN1y5xQbxyRCe QjEOeNtSfLXVq5wDI6nKNxFZRSKACRLIYWPA+GaGU2Ni/ZBj4SqaqrZfQ4hw4jow5vVI KNig== X-Gm-Message-State: AO0yUKUpqLjMPmyg0aqv1YP07hLaKDSEVqs2xvmVTfkn0zcd2AWCSYQu DSK2v/ILSl2jThU3ADqVdfgVmuvbiyhfkOl6au9hATmyPw+1VAMk/J/+aRypPFfe4VgeWFQ8GvI HBXqB3jbVMWmA+P+Md1YiPw== X-Received: by 2002:a05:6000:1f05:b0:2bf:bc38:17c1 with SMTP id bv5-20020a0560001f0500b002bfbc3817c1mr9332018wrb.4.1674835949251; Fri, 27 Jan 2023 08:12:29 -0800 (PST) X-Google-Smtp-Source: AK7set9xHxRFMELkql7GhWmWFY9SeZNG8Y1DmSr6SFxhFl3Z+1haelg4X8dDIm2uqRediNz9/rRjDw== X-Received: by 2002:a05:6000:1f05:b0:2bf:bc38:17c1 with SMTP id bv5-20020a0560001f0500b002bfbc3817c1mr9331981wrb.4.1674835948989; Fri, 27 Jan 2023 08:12:28 -0800 (PST) Received: from ?IPV6:2003:d8:2f16:1800:a9b4:1776:c5d9:1d9a? (p200300d82f161800a9b41776c5d91d9a.dip0.t-ipconnect.de. [2003:d8:2f16:1800:a9b4:1776:c5d9:1d9a]) by smtp.gmail.com with ESMTPSA id e21-20020a5d5955000000b002b57bae7174sm4283915wri.5.2023.01.27.08.12.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 27 Jan 2023 08:12:28 -0800 (PST) Message-ID: Date: Fri, 27 Jan 2023 17:12:26 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH v5 18/39] mm: Handle faultless write upgrades for shstk Content-Language: en-US To: "Edgecombe, Rick P" , "bsingharora@gmail.com" , "hpa@zytor.com" , "Syromiatnikov, Eugene" , "peterz@infradead.org" , "rdunlap@infradead.org" , "keescook@chromium.org" , "Eranian, Stephane" , "kirill.shutemov@linux.intel.com" , "dave.hansen@linux.intel.com" , "linux-mm@kvack.org" , "fweimer@redhat.com" , "nadav.amit@gmail.com" , "jannh@google.com" , "dethoma@microsoft.com" , "kcc@google.com" , "linux-arch@vger.kernel.org" , "pavel@ucw.cz" , "oleg@redhat.com" , "hjl.tools@gmail.com" , "akpm@linux-foundation.org" , "Lutomirski, Andy" , "bp@alien8.de" , "jamorris@linux.microsoft.com" , "Yang, Weijiang" , "Schimpe, Christina" , "mike.kravetz@oracle.com" , "arnd@arndb.de" , "linux-doc@vger.kernel.org" , "x86@kernel.org" , "tglx@linutronix.de" , "andrew.cooper3@citrix.com" , "john.allen@amd.com" , "rppt@kernel.org" , "mingo@redhat.com" , "corbet@lwn.net" , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" , "gorcunov@gmail.com" Cc: "Yu, Yu-cheng" References: <20230119212317.8324-1-rick.p.edgecombe@intel.com> <20230119212317.8324-19-rick.p.edgecombe@intel.com> <7f63d13d-7940-afb6-8b25-26fdf3804e00@redhat.com> <50cf64932507ba60639eca28692e7df285bcc0a7.camel@intel.com> <1327c608-1473-af4f-d962-c24f04f3952c@redhat.com> <8c3820ae1448de4baffe7c476b4b5d9ba0a309ff.camel@intel.com> <4d224020-f26f-60a4-c7ab-721a024c7a6d@redhat.com> <899d8f3baaf45b896cf335dec2143cd0969a2d8a.camel@intel.com> <27b141c06c37da78afca7214ec7efeaf730162d9.camel@intel.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <27b141c06c37da78afca7214ec7efeaf730162d9.camel@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On 26.01.23 21:19, Edgecombe, Rick P wrote: > On Thu, 2023-01-26 at 09:46 +0100, David Hildenbrand wrote: >> On 26.01.23 01:59, Edgecombe, Rick P wrote: >>> On Wed, 2023-01-25 at 10:43 -0800, Rick Edgecombe wrote: >>>> Thanks for your comments and ideas here, I'll give the: >>>> pte_t pte_mkwrite(struct vm_area_struct *vma, pte_t pte) >>>> ...solution a try. >>> >>> Well, it turns out there are some pte_mkwrite() callers in other >>> arch's >>> that operate on kernel memory and don't have a VMA. So it needed a >>> new >> >> Why not pass in NULL as VMA then and document the semantics? The >> less >> similarly named but slightly different functions, the better :) > > Hmm. The x86 and generic versions should probably have the same > semantics, so then if you pass a NULL, it would do a regular > pte_mkwrite() I guess? > > I see another benefit of requiring the vma argument, such that raw > pte_mkwrite()s are less likely to appear in core MM code. But I think > the NULL is awkward because it's not obvious, to me at least, what the > implications of that should be. > > So it will be confusing to read in the NULL cases for the other archs. > We also have some warnings to catch miss cases in the PTE tear down > code, so the scenario of new code accidentally marking shadow stack > PTEs as writable is not totally unchecked. > > The three functions that do slightly different things are: > > pte_mkwrite(): > Makes a PTE conventionally writable, only takes a PTE. Very clear that > it is a low level helper and what it does. > > maybe_mkwrite(): > Might make a PTE writable if the VMA allows it. > > pte_mkwrite_vma(): > Makes a PTE writable in a specific way depending on the VMA > > I wonder if the name pte_mkwrite_vma() is maybe just not clear enough. > It takes a VMA, yes, but what does it do with it? > > What if it was called pte_mkwrite_type() instead? Some arch's have > additional types of writable memory and this function creates them. Of > course they also have the normal type of writable memory, and > pte_mkwrite() creates that like usual. Doesn't it seem more readable? The issue is, the more variants we provide the easier it is to make mistakes and introduce new buggy code. It's tempting to simply use pte_mkwrite() and call it a day, where people actually should use pte_mkwrite_vma(). Then, they at least have to investigate what to do about the second VMA parameter. -- Thanks, David / dhildenb