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=-1.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 0FE05C49ED6 for ; Wed, 11 Sep 2019 10:38:06 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 D37042087E for ; Wed, 11 Sep 2019 10:38:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="S+ChfS3z" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D37042087E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=cyphar.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-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=bombadil.20170209; h=Sender:Content-Type:Cc: List-Subscribe:List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id: In-Reply-To:MIME-Version:References:Message-ID:Subject:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=bjWWkl+0H29TaFQqwhqLRGg/rvJELnd5N4FdImkqTF4=; b=S+ChfS3zyksf1ZaJMFSbzONWf MxB92PN3bIHjWS32FjviMjwia4wozpKXzIy/ggbY/53/KsLF+PFEkyCQVkYVlpBCyvqDaAHWkn6Ei EZ9Mma3T04iy9jM0MdIUeAPLSebbgCibRIJs504vIklLBPEvqPA0GXhLVUB0z5nctnQZKjzC5wgMT sIOoZvHUN5yLbbsr5Cvfs2TFtWlo6ikHYQAZZaN2zwR64BBRGQBCycbSUZkT3bo6pxvQp6ylx+5Hx S2GC+5C9o5Ffy9HJcim78A/M3HJM4rU0pNaFKnGHk/9/GSlNubH3iavUwafHJ+aI7Ocjx2oKNojRt bcZZrlm8A==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1i800d-0000b8-2U; Wed, 11 Sep 2019 10:37:59 +0000 Received: from mx2a.mailbox.org ([80.241.60.219]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1i800X-0000ag-Bl for linux-arm-kernel@lists.infradead.org; Wed, 11 Sep 2019 10:37:56 +0000 Received: from smtp1.mailbox.org (smtp1.mailbox.org [80.241.60.240]) (using TLSv1.2 with cipher ECDHE-RSA-CHACHA20-POLY1305 (256/256 bits)) (No client certificate requested) by mx2.mailbox.org (Postfix) with ESMTPS id AC930A2C82; Wed, 11 Sep 2019 12:37:46 +0200 (CEST) X-Virus-Scanned: amavisd-new at heinlein-support.de Received: from smtp1.mailbox.org ([80.241.60.240]) by spamfilter04.heinlein-hosting.de (spamfilter04.heinlein-hosting.de [80.241.56.122]) (amavisd-new, port 10030) with ESMTP id ATeziMSY9H4D; Wed, 11 Sep 2019 12:37:41 +0200 (CEST) Date: Wed, 11 Sep 2019 20:37:30 +1000 From: Aleksa Sarai To: Peter Zijlstra Subject: Re: [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers Message-ID: <20190911103730.72unmfp7lsvvafxo@yavin> References: <20190904201933.10736-1-cyphar@cyphar.com> <20190904201933.10736-2-cyphar@cyphar.com> <20190905073205.GY2332@hirez.programming.kicks-ass.net> <20190905092622.tlb6nn3uisssdfbu@yavin.dot.cyphar.com> <20190905094305.GJ2349@hirez.programming.kicks-ass.net> <20190905105749.GW2386@hirez.programming.kicks-ass.net> MIME-Version: 1.0 In-Reply-To: <20190905105749.GW2386@hirez.programming.kicks-ass.net> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190911_033754_544957_99E00E9E X-CRM114-Status: GOOD ( 28.54 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, Alexander Shishkin , Rasmus Villemoes , Alexei Starovoitov , linux-kernel@vger.kernel.org, David Howells , linux-kselftest@vger.kernel.org, sparclinux@vger.kernel.org, Jiri Olsa , linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, Tycho Andersen , Aleksa Sarai , Shuah Khan , Ingo Molnar , linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, linux-xtensa@linux-xtensa.org, Kees Cook , Arnd Bergmann , Jann Horn , linuxppc-dev@lists.ozlabs.org, linux-m68k@lists.linux-m68k.org, Al Viro , Andy Lutomirski , Shuah Khan , Namhyung Kim , David Drysdale , Christian Brauner , "J. Bruce Fields" , linux-parisc@vger.kernel.org, linux-api@vger.kernel.org, Chanho Min , Jeff Layton , Oleg Nesterov , patrick.bellasi@arm.com, Eric Biederman , linux-alpha@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Linus Torvalds , containers@lists.linux-foundation.org Content-Type: multipart/mixed; boundary="===============3127660236630967693==" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org --===============3127660236630967693== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="xpghzs3x7rsccuuz" Content-Disposition: inline --xpghzs3x7rsccuuz Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2019-09-05, Peter Zijlstra wrote: > On Thu, Sep 05, 2019 at 11:43:05AM +0200, Peter Zijlstra wrote: > > On Thu, Sep 05, 2019 at 07:26:22PM +1000, Aleksa Sarai wrote: > > > On 2019-09-05, Peter Zijlstra wrote: > > > > On Thu, Sep 05, 2019 at 06:19:22AM +1000, Aleksa Sarai wrote: > > > > > +/** > > > > > + * copy_struct_to_user: copy a struct to user space > > > > > + * @dst: Destination address, in user space. > > > > > + * @usize: Size of @dst struct. > > > > > + * @src: Source address, in kernel space. > > > > > + * @ksize: Size of @src struct. > > > > > + * > > > > > + * Copies a struct from kernel space to user space, in a way tha= t guarantees > > > > > + * backwards-compatibility for struct syscall arguments (as long= as future > > > > > + * struct extensions are made such that all new fields are *appe= nded* to the > > > > > + * old struct, and zeroed-out new fields have the same meaning a= s the old > > > > > + * struct). > > > > > + * > > > > > + * @ksize is just sizeof(*dst), and @usize should've been passed= by user space. > > > > > + * The recommended usage is something like the following: > > > > > + * > > > > > + * SYSCALL_DEFINE2(foobar, struct foo __user *, uarg, size_t, = usize) > > > > > + * { > > > > > + * int err; > > > > > + * struct foo karg =3D {}; > > > > > + * > > > > > + * // do something with karg > > > > > + * > > > > > + * err =3D copy_struct_to_user(uarg, usize, &karg, sizeof(k= arg)); > > > > > + * if (err) > > > > > + * return err; > > > > > + * > > > > > + * // ... > > > > > + * } > > > > > + * > > > > > + * There are three cases to consider: > > > > > + * * If @usize =3D=3D @ksize, then it's copied verbatim. > > > > > + * * If @usize < @ksize, then kernel space is "returning" a new= er struct to an > > > > > + * older user space. In order to avoid user space getting inc= omplete > > > > > + * information (new fields might be important), all trailing = bytes in @src > > > > > + * (@ksize - @usize) must be zerored > > > >=20 > > > > s/zerored/zero/, right? > > >=20 > > > It should've been "zeroed". > >=20 > > That reads wrong to me; that way it reads like this function must take > > that action and zero out the 'rest'; which is just wrong. > >=20 > > This function must verify those bytes are zero, not make them zero. > >=20 > > > > > , otherwise -EFBIG is re= turned. > > > >=20 > > > > 'Funny' that, copy_struct_from_user() below seems to use E2BIG. > > >=20 > > > This is a copy of the semantics that sched_[sg]etattr(2) uses -- E2BI= G for > > > a "too big" struct passed to the kernel, and EFBIG for a "too big" > > > struct passed to user-space. I would personally have preferred EMSGSI= ZE > > > instead of EFBIG, but felt using the existing error codes would be le= ss > > > confusing. > >=20 > > Sadly a recent commit: > >=20 > > 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and robustify= sched_read_attr() ABI logic and code") > >=20 > > Made the situation even 'worse'. >=20 > And thinking more about things; I'm not convinced the above patch is > actually right. >=20 > Do we really want to simply truncate all the attributes of the task? >=20 > And should we not at least set sched_flags when there are non-default > clamp values applied? >=20 > See; that is I think the primary bug that had chrt failing; we tried to > publish the default clamp values as !0. I just saw this patch in -rc8 -- should I even attempt to port sched_getattr(2) to copy_struct_to_user()? I agree that publishing a default non-zero value is a mistake -- once you do that, old user space will either get confused or lose information. --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --xpghzs3x7rsccuuz Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSxZm6dtfE8gxLLfYqdlLljIbnQEgUCXXjOZwAKCRCdlLljIbnQ EgeZAP9UC+Kf1AuY3XgSz6a5avhF1Eskr6DzrSR4wx0T62dnoQD9GcCXU0oVrERB 0xz5K9MrU1nBr6ERqmBwygo/DVsTwAk= =oep8 -----END PGP SIGNATURE----- --xpghzs3x7rsccuuz-- --===============3127660236630967693== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel --===============3127660236630967693==--