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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 1D820C83003 for ; Wed, 29 Apr 2020 13:52:32 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D433F208FE for ; Wed, 29 Apr 2020 13:52:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D433F208FE Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 5F7A98E0007; Wed, 29 Apr 2020 09:52:31 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5A8178E0005; Wed, 29 Apr 2020 09:52:31 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4BDBD8E0007; Wed, 29 Apr 2020 09:52:31 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0238.hostedemail.com [216.40.44.238]) by kanga.kvack.org (Postfix) with ESMTP id 33FBB8E0005 for ; Wed, 29 Apr 2020 09:52:31 -0400 (EDT) Received: from smtpin26.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id D780C2A87 for ; Wed, 29 Apr 2020 13:52:30 +0000 (UTC) X-FDA: 76761032460.26.hen85_32fe499584555 X-HE-Tag: hen85_32fe499584555 X-Filterd-Recvd-Size: 3800 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf10.hostedemail.com (Postfix) with ESMTP for ; Wed, 29 Apr 2020 13:52:30 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 699A61045; Wed, 29 Apr 2020 06:52:29 -0700 (PDT) Received: from gaia (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B2B563F68F; Wed, 29 Apr 2020 06:52:27 -0700 (PDT) Date: Wed, 29 Apr 2020 14:52:25 +0100 From: Catalin Marinas To: Dave Martin Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, Richard Earnshaw , Szabolcs Nagy , Andrey Konovalov , Kevin Brodsky , Peter Collingbourne , linux-mm@kvack.org, Alexander Viro , Vincenzo Frascino , Will Deacon Subject: Re: [PATCH v3 20/23] fs: Allow copy_mount_options() to access user-space in a single pass Message-ID: <20200429135224.GB10651@gaia> References: <20200421142603.3894-1-catalin.marinas@arm.com> <20200421142603.3894-21-catalin.marinas@arm.com> <20200429102650.GC30377@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200429102650.GC30377@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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 Wed, Apr 29, 2020 at 11:26:51AM +0100, Dave P Martin wrote: > On Tue, Apr 21, 2020 at 03:26:00PM +0100, Catalin Marinas wrote: > > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h > > index 32fc8061aa76..566da441eba2 100644 > > --- a/arch/arm64/include/asm/uaccess.h > > +++ b/arch/arm64/include/asm/uaccess.h > > @@ -416,6 +416,17 @@ extern unsigned long __must_check __arch_copy_in_user(void __user *to, const voi > > #define INLINE_COPY_TO_USER > > #define INLINE_COPY_FROM_USER > > > > +static inline bool arch_has_exact_copy_from_user(unsigned long n) > > +{ > > + /* > > + * copy_from_user() aligns the source pointer if the size is greater > > + * than 15. Since all the loads are naturally aligned, they can only > > + * fail on the first byte. > > + */ > > + return n > 15; > > +} > > +#define arch_has_exact_copy_from_user > > Did you mean: > > #define arch_has_exact_copy_from_user arch_has_exact_copy_from_user Yes (and I shouldn't write patches late in the day). > Mind you, if this expands to 1 I'd have expected copy_mount_options() > not to compile, so I may be missing something. I think arch_has_exact_copy_from_user() (with the braces) is looked up in the function namespace, so the macro isn't expanded. So arguably the patch is correct but pretty dodgy ;). I scrapped this in my second attempt in reply to Kevin. > > diff --git a/fs/namespace.c b/fs/namespace.c > > index a28e4db075ed..8febc50dfc5d 100644 > > --- a/fs/namespace.c > > +++ b/fs/namespace.c > > @@ -3025,13 +3025,16 @@ void *copy_mount_options(const void __user * data) > > [ Is this applying a band-aid to duct tape? > > The fs presumably knows ahead of time whether it's expecting a string or > a fixed-size blob for data, so I'd hope we could just DTRT rather than > playing SEGV roulette here. > > This might require more refactoring than makes sense for this series > though. ] That's possible but it means moving the copy from sys_mount() to the specific places where it has additional information (the filesystems). I'm not even sure it's guaranteed to be strings. If it is, we could just replace all this with a strncpy_from_user(). -- Catalin