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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 87568C433ED for ; Tue, 18 May 2021 16:02:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 70CC761028 for ; Tue, 18 May 2021 16:02:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350232AbhERQDj (ORCPT ); Tue, 18 May 2021 12:03:39 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:41974 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344303AbhERQDe (ORCPT ); Tue, 18 May 2021 12:03:34 -0400 Received: from in01.mta.xmission.com ([166.70.13.51]) by out02.mta.xmission.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1lj2Ac-00AUYJ-9D; Tue, 18 May 2021 10:02:10 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=fess.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1lj2AZ-0004Ye-GI; Tue, 18 May 2021 10:02:10 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Arnd Bergmann Cc: linux-arch , Christoph Hellwig , Alexander Viro , Andrew Morton , Borislav Petkov , Brian Gerst , Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner , Linux ARM , Linux Kernel Mailing List , Linux-MM , kexec@lists.infradead.org References: <20210517203343.3941777-1-arnd@kernel.org> <20210517203343.3941777-2-arnd@kernel.org> Date: Tue, 18 May 2021 11:01:57 -0500 In-Reply-To: (Arnd Bergmann's message of "Tue, 18 May 2021 16:17:53 +0200") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1lj2AZ-0004Ye-GI;;;mid=;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1/3KUt9n9NsCywLTywTeK8LOKWYroFccQo= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH v3 1/4] kexec: simplify compat_sys_kexec_load X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Arnd Bergmann writes: > On Tue, May 18, 2021 at 4:05 PM Arnd Bergmann wrote: >> >> On Tue, May 18, 2021 at 3:41 PM Eric W. Biederman wrote: >> > >> > Arnd Bergmann writes: >> > >> > > From: Arnd Bergmann KEXEC_ARCH_DEFAULT >> > > >> > > The compat version of sys_kexec_load() uses compat_alloc_user_space to >> > > convert the user-provided arguments into the native format. >> > > >> > > Move the conversion into the regular implementation with >> > > an in_compat_syscall() check to simplify it and avoid the >> > > compat_alloc_user_space() call. >> > > >> > > compat_sys_kexec_load() now behaves the same as sys_kexec_load(). >> > >> > Nacked-by: "Eric W. Biederman" >> >KEXEC_ARCH_DEFAULT >> > The patch is wrong. >> > >> > The logic between the compat entry point and the ordinary entry point >> > are by necessity different. This unifies the logic and breaks the compat >> > entry point. >> > >> > The fundamentally necessity is that the code being loaded needs to know >> > which mode the kernel is running in so it can safely transition to the >> > new kernel. >> > >> > Given that the two entry points fundamentally need different logic, >> > and that difference was not preserved and the goal of this patchset >> > was to unify that which fundamentally needs to be different. I don't >> > think this patch series makes any sense for kexec. >> >> Sorry, I'm not following that explanation. Can you clarify what different >> modes of the kernel you are referring to here, and how my patch >> changes this? > > I think I figured it out now myself after comparing the two functions: > > --- a/kernel/kexec.c > +++ b/kernel/kexec.c > @@ -269,7 +269,8 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, > unsigned long, nr_segments, > > /* Verify we are on the appropriate architecture */ > if (((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH) && > - ((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT)) > + (in_compat_syscall() || > + ((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT))) > return -EINVAL; > > /* Because we write directly to the reserved memory > > Not sure if that's the best way of doing it, but it looks like folding this > in restores the current behavior. Yes. That is pretty much all there is. I personally can't stand the sight of in_compat_syscall() doubly so when you have to lie to the type system with casts. The cognitive dissonance I experience is extreme. I will be happy to help you find another way to get rid of compat_alloc_user, but not that way. There is a whole mess in there that was introduced when someone added do_kexec_load while I was napping in 2017 that makes the system calls an absolute mess. It all needs to be cleaned up. Eric 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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 2B7FFC433B4 for ; Tue, 18 May 2021 16:02:22 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D4F7961028 for ; Tue, 18 May 2021 16:02:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D4F7961028 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=xmission.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 36B9B6B00E7; Tue, 18 May 2021 12:02:21 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 343766B00E8; Tue, 18 May 2021 12:02:21 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 20C486B00E9; Tue, 18 May 2021 12:02:21 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0110.hostedemail.com [216.40.44.110]) by kanga.kvack.org (Postfix) with ESMTP id E877B6B00E7 for ; Tue, 18 May 2021 12:02:20 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 91A10A8D0 for ; Tue, 18 May 2021 16:02:20 +0000 (UTC) X-FDA: 78154818840.21.C240420 Received: from out02.mta.xmission.com (out02.mta.xmission.com [166.70.13.232]) by imf04.hostedemail.com (Postfix) with ESMTP id 8D86178F for ; Tue, 18 May 2021 16:02:17 +0000 (UTC) Received: from in01.mta.xmission.com ([166.70.13.51]) by out02.mta.xmission.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1lj2Ac-00AUYJ-9D; Tue, 18 May 2021 10:02:10 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=fess.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1lj2AZ-0004Ye-GI; Tue, 18 May 2021 10:02:10 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Arnd Bergmann Cc: linux-arch , Christoph Hellwig , Alexander Viro , Andrew Morton , Borislav Petkov , Brian Gerst , Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner , Linux ARM , Linux Kernel Mailing List , Linux-MM , kexec@lists.infradead.org References: <20210517203343.3941777-1-arnd@kernel.org> <20210517203343.3941777-2-arnd@kernel.org> Date: Tue, 18 May 2021 11:01:57 -0500 In-Reply-To: (Arnd Bergmann's message of "Tue, 18 May 2021 16:17:53 +0200") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1lj2AZ-0004Ye-GI;;;mid=;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1/3KUt9n9NsCywLTywTeK8LOKWYroFccQo= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH v3 1/4] kexec: simplify compat_sys_kexec_load X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) X-Rspamd-Queue-Id: 8D86178F Authentication-Results: imf04.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=xmission.com; spf=pass (imf04.hostedemail.com: domain of ebiederm@xmission.com designates 166.70.13.232 as permitted sender) smtp.mailfrom=ebiederm@xmission.com X-Rspamd-Server: rspam04 X-Stat-Signature: n88umw6a7ufzt4cuchsa8df3e3uqusax X-HE-Tag: 1621353737-188254 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: Arnd Bergmann writes: > On Tue, May 18, 2021 at 4:05 PM Arnd Bergmann wrote: >> >> On Tue, May 18, 2021 at 3:41 PM Eric W. Biederman wrote: >> > >> > Arnd Bergmann writes: >> > >> > > From: Arnd Bergmann KEXEC_ARCH_DEFAULT >> > > >> > > The compat version of sys_kexec_load() uses compat_alloc_user_space to >> > > convert the user-provided arguments into the native format. >> > > >> > > Move the conversion into the regular implementation with >> > > an in_compat_syscall() check to simplify it and avoid the >> > > compat_alloc_user_space() call. >> > > >> > > compat_sys_kexec_load() now behaves the same as sys_kexec_load(). >> > >> > Nacked-by: "Eric W. Biederman" >> >KEXEC_ARCH_DEFAULT >> > The patch is wrong. >> > >> > The logic between the compat entry point and the ordinary entry point >> > are by necessity different. This unifies the logic and breaks the compat >> > entry point. >> > >> > The fundamentally necessity is that the code being loaded needs to know >> > which mode the kernel is running in so it can safely transition to the >> > new kernel. >> > >> > Given that the two entry points fundamentally need different logic, >> > and that difference was not preserved and the goal of this patchset >> > was to unify that which fundamentally needs to be different. I don't >> > think this patch series makes any sense for kexec. >> >> Sorry, I'm not following that explanation. Can you clarify what different >> modes of the kernel you are referring to here, and how my patch >> changes this? > > I think I figured it out now myself after comparing the two functions: > > --- a/kernel/kexec.c > +++ b/kernel/kexec.c > @@ -269,7 +269,8 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, > unsigned long, nr_segments, > > /* Verify we are on the appropriate architecture */ > if (((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH) && > - ((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT)) > + (in_compat_syscall() || > + ((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT))) > return -EINVAL; > > /* Because we write directly to the reserved memory > > Not sure if that's the best way of doing it, but it looks like folding this > in restores the current behavior. Yes. That is pretty much all there is. I personally can't stand the sight of in_compat_syscall() doubly so when you have to lie to the type system with casts. The cognitive dissonance I experience is extreme. I will be happy to help you find another way to get rid of compat_alloc_user, but not that way. There is a whole mess in there that was introduced when someone added do_kexec_load while I was napping in 2017 that makes the system calls an absolute mess. It all needs to be cleaned up. Eric 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=-14.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 285E4C433ED for ; Tue, 18 May 2021 16:04:49 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id AABDF611AC for ; Tue, 18 May 2021 16:04:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AABDF611AC Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=xmission.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=desiato.20200630; h=Sender:Content-Transfer-Encoding :Content-Type:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:Subject:MIME-Version:Message-ID:In-Reply-To:Date: References:Cc:To:From:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=VOIiXZJcbrt3wQb63myx+olmkFJaJ0RWle9sDJEIYqs=; b=ppza24mbE2FC8GJZEmTChidOn fqpi1BD7WTn4xoWIb7JdlFpa7tL4GBTawY/LhsSuFHD7OUv3ujnkz73CtbPYFz2S6HOSmdOZKnJ4z dPLaz0PI3ne8Cmi9Yskx5wd2sWRCZqguE5uoIkUhyy9me2fZ/S1FnsYKD7KBrkTCno5GukonKt9Q9 eXgXfudiOGUUAF8sCg11IfZdMzULq8Oiuw0yVPIw973EARaLDsK5YV9uNfvldumaDA5lTA4UNwC0B wugoLZEwkVTp07W4+NwpVpN/gMdXGKI/g23ky4AnrKBw2DcsCgUQLRtNzGEO8uLxoSfSf/dkgw96B TTs52GiTQ==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1lj2BW-001GIN-28; Tue, 18 May 2021 16:03:08 +0000 Received: from bombadil.infradead.org ([2607:7c80:54:e::133]) by desiato.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lj2BF-001GH3-QR; Tue, 18 May 2021 16:02:50 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Subject:Content-Type:MIME-Version: Message-ID:In-Reply-To:Date:References:Cc:To:From:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=5SD47w6p/6kkCVEvZHxddqk5ay0gVNriztl42vSnXAM=; b=kfRLBoOtQksRWOIcRfU/7O3sr8 8QTLV+eCud6D0LgD8gghBtaCI6OMtl92XmnzM9PYW3c7X1C02v3/B+t52FprOwT5XdfNCk7CiNVTy pBNakIdCBzXJSwKkoZ8MTK7Cn1CPlqFf9l6JpJRc1J8MsIUR8HBaB73cfLSHrqvZB4S//GsFAuixt T7O2dVCUosI1tqAC0c8Pw3rTaC12zkVG+npBlHwsQMT/+pPRYRzR6ocO9/z8Yshj3jlVqQsXg8J40 he/Rauac0QoDd/QfYYnkJT/VSKEqSKID2mtDKwAQONjTLqy0gfZOhdIZD3MxGNMs1k8/mHzOK1EaN 7s4yt6YA==; Received: from out02.mta.xmission.com ([166.70.13.232]) by bombadil.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lj2BC-00Emig-MR; Tue, 18 May 2021 16:02:48 +0000 Received: from in01.mta.xmission.com ([166.70.13.51]) by out02.mta.xmission.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1lj2Ac-00AUYJ-9D; Tue, 18 May 2021 10:02:10 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=fess.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1lj2AZ-0004Ye-GI; Tue, 18 May 2021 10:02:10 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Arnd Bergmann Cc: linux-arch , Christoph Hellwig , Alexander Viro , Andrew Morton , Borislav Petkov , Brian Gerst , Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner , Linux ARM , Linux Kernel Mailing List , Linux-MM , kexec@lists.infradead.org References: <20210517203343.3941777-1-arnd@kernel.org> <20210517203343.3941777-2-arnd@kernel.org> Date: Tue, 18 May 2021 11:01:57 -0500 In-Reply-To: (Arnd Bergmann's message of "Tue, 18 May 2021 16:17:53 +0200") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 X-XM-SPF: eid=1lj2AZ-0004Ye-GI; ; ; mid=; ; ; hst=in01.mta.xmission.com; ; ; ip=68.227.160.95; ; ; frm=ebiederm@xmission.com; ; ; spf=neutral X-XM-AID: U2FsdGVkX1/3KUt9n9NsCywLTywTeK8LOKWYroFccQo= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH v3 1/4] kexec: simplify compat_sys_kexec_load X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210518_090246_755065_49929D8F X-CRM114-Status: GOOD ( 33.26 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Arnd Bergmann writes: > On Tue, May 18, 2021 at 4:05 PM Arnd Bergmann wrote: >> >> On Tue, May 18, 2021 at 3:41 PM Eric W. Biederman wrote: >> > >> > Arnd Bergmann writes: >> > >> > > From: Arnd Bergmann KEXEC_ARCH_DEFAULT >> > > >> > > The compat version of sys_kexec_load() uses compat_alloc_user_space to >> > > convert the user-provided arguments into the native format. >> > > >> > > Move the conversion into the regular implementation with >> > > an in_compat_syscall() check to simplify it and avoid the >> > > compat_alloc_user_space() call. >> > > >> > > compat_sys_kexec_load() now behaves the same as sys_kexec_load(). >> > >> > Nacked-by: "Eric W. Biederman" >> >KEXEC_ARCH_DEFAULT >> > The patch is wrong. >> > >> > The logic between the compat entry point and the ordinary entry point >> > are by necessity different. This unifies the logic and breaks the compat >> > entry point. >> > >> > The fundamentally necessity is that the code being loaded needs to know >> > which mode the kernel is running in so it can safely transition to the >> > new kernel. >> > >> > Given that the two entry points fundamentally need different logic, >> > and that difference was not preserved and the goal of this patchset >> > was to unify that which fundamentally needs to be different. I don't >> > think this patch series makes any sense for kexec. >> >> Sorry, I'm not following that explanation. Can you clarify what different >> modes of the kernel you are referring to here, and how my patch >> changes this? > > I think I figured it out now myself after comparing the two functions: > > --- a/kernel/kexec.c > +++ b/kernel/kexec.c > @@ -269,7 +269,8 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, > unsigned long, nr_segments, > > /* Verify we are on the appropriate architecture */ > if (((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH) && > - ((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT)) > + (in_compat_syscall() || > + ((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT))) > return -EINVAL; > > /* Because we write directly to the reserved memory > > Not sure if that's the best way of doing it, but it looks like folding this > in restores the current behavior. Yes. That is pretty much all there is. I personally can't stand the sight of in_compat_syscall() doubly so when you have to lie to the type system with casts. The cognitive dissonance I experience is extreme. I will be happy to help you find another way to get rid of compat_alloc_user, but not that way. There is a whole mess in there that was introduced when someone added do_kexec_load while I was napping in 2017 that makes the system calls an absolute mess. It all needs to be cleaned up. Eric _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: From: ebiederm@xmission.com (Eric W. Biederman) References: <20210517203343.3941777-1-arnd@kernel.org> <20210517203343.3941777-2-arnd@kernel.org> Date: Tue, 18 May 2021 11:01:57 -0500 In-Reply-To: (Arnd Bergmann's message of "Tue, 18 May 2021 16:17:53 +0200") Message-ID: MIME-Version: 1.0 Subject: Re: [PATCH v3 1/4] kexec: simplify compat_sys_kexec_load List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Arnd Bergmann Cc: linux-arch , Christoph Hellwig , Alexander Viro , Andrew Morton , Borislav Petkov , Brian Gerst , Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner , Linux ARM , Linux Kernel Mailing List , Linux-MM , kexec@lists.infradead.org Arnd Bergmann writes: > On Tue, May 18, 2021 at 4:05 PM Arnd Bergmann wrote: >> >> On Tue, May 18, 2021 at 3:41 PM Eric W. Biederman wrote: >> > >> > Arnd Bergmann writes: >> > >> > > From: Arnd Bergmann KEXEC_ARCH_DEFAULT >> > > >> > > The compat version of sys_kexec_load() uses compat_alloc_user_space to >> > > convert the user-provided arguments into the native format. >> > > >> > > Move the conversion into the regular implementation with >> > > an in_compat_syscall() check to simplify it and avoid the >> > > compat_alloc_user_space() call. >> > > >> > > compat_sys_kexec_load() now behaves the same as sys_kexec_load(). >> > >> > Nacked-by: "Eric W. Biederman" >> >KEXEC_ARCH_DEFAULT >> > The patch is wrong. >> > >> > The logic between the compat entry point and the ordinary entry point >> > are by necessity different. This unifies the logic and breaks the compat >> > entry point. >> > >> > The fundamentally necessity is that the code being loaded needs to know >> > which mode the kernel is running in so it can safely transition to the >> > new kernel. >> > >> > Given that the two entry points fundamentally need different logic, >> > and that difference was not preserved and the goal of this patchset >> > was to unify that which fundamentally needs to be different. I don't >> > think this patch series makes any sense for kexec. >> >> Sorry, I'm not following that explanation. Can you clarify what different >> modes of the kernel you are referring to here, and how my patch >> changes this? > > I think I figured it out now myself after comparing the two functions: > > --- a/kernel/kexec.c > +++ b/kernel/kexec.c > @@ -269,7 +269,8 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, > unsigned long, nr_segments, > > /* Verify we are on the appropriate architecture */ > if (((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH) && > - ((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT)) > + (in_compat_syscall() || > + ((flags & KEXEC_ARCH_MASK) != KEXEC_ARCH_DEFAULT))) > return -EINVAL; > > /* Because we write directly to the reserved memory > > Not sure if that's the best way of doing it, but it looks like folding this > in restores the current behavior. Yes. That is pretty much all there is. I personally can't stand the sight of in_compat_syscall() doubly so when you have to lie to the type system with casts. The cognitive dissonance I experience is extreme. I will be happy to help you find another way to get rid of compat_alloc_user, but not that way. There is a whole mess in there that was introduced when someone added do_kexec_load while I was napping in 2017 that makes the system calls an absolute mess. It all needs to be cleaned up. Eric _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec