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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 D11EFC83003 for ; Wed, 29 Apr 2020 10:26:56 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7B1ED2073E for ; Wed, 29 Apr 2020 10:26:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7B1ED2073E 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 2E8098E0005; Wed, 29 Apr 2020 06:26:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2998A8E0001; Wed, 29 Apr 2020 06:26:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1AF938E0005; Wed, 29 Apr 2020 06:26:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0059.hostedemail.com [216.40.44.59]) by kanga.kvack.org (Postfix) with ESMTP id 04F168E0001 for ; Wed, 29 Apr 2020 06:26:56 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id B65A2180AD807 for ; Wed, 29 Apr 2020 10:26:55 +0000 (UTC) X-FDA: 76760514390.21.ant59_23d2cebb3c07 X-HE-Tag: ant59_23d2cebb3c07 X-Filterd-Recvd-Size: 5236 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf06.hostedemail.com (Postfix) with ESMTP for ; Wed, 29 Apr 2020 10:26:55 +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 A6410C14; Wed, 29 Apr 2020 03:26:54 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 218AA3F73D; Wed, 29 Apr 2020 03:26:53 -0700 (PDT) Date: Wed, 29 Apr 2020 11:26:51 +0100 From: Dave Martin To: Catalin Marinas 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: <20200429102650.GC30377@arm.com> References: <20200421142603.3894-1-catalin.marinas@arm.com> <20200421142603.3894-21-catalin.marinas@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200421142603.3894-21-catalin.marinas@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) 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 Tue, Apr 21, 2020 at 03:26:00PM +0100, Catalin Marinas wrote: > The copy_mount_options() function takes a user pointer argument but not > a size. It tries to read up to a PAGE_SIZE. However, copy_from_user() is > not guaranteed to return all the accessible bytes if, for example, the > access crosses a page boundary and gets a fault on the second page. To > work around this, the current copy_mount_options() implementations > performs to copy_from_user() passes, first to the end of the current implementation performs two > page and the second to what's left in the subsequent page. > > Some architectures like arm64 can guarantee an exact copy_from_user() > depending on the size (since the arch function performs some alignment > on the source register). Introduce an arch_has_exact_copy_from_user() > function and allow copy_mount_options() to perform the user access in a > single pass. > > While this function is not on a critical path, the single-pass behaviour > is required for arm64 MTE (memory tagging) support where a uaccess can > trigger intra-page faults (tag not matching). With the current > implementation, if this happens during the first page, the function will > return -EFAULT. > > Signed-off-by: Catalin Marinas > Cc: Alexander Viro > Cc: Will Deacon > --- > > Notes: > New in v3. > > arch/arm64/include/asm/uaccess.h | 11 +++++++++++ > fs/namespace.c | 7 +++++-- > include/linux/uaccess.h | 8 ++++++++ > 3 files changed, 24 insertions(+), 2 deletions(-) > > 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 Mind you, if this expands to 1 I'd have expected copy_mount_options() not to compile, so I may be missing something. [...] > 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. ] > if (!copy) > return ERR_PTR(-ENOMEM); > > - size = PAGE_SIZE - offset_in_page(data); > + size = PAGE_SIZE; > + if (!arch_has_exact_copy_from_user(size)) > + size -= offset_in_page(data); > > - if (copy_from_user(copy, data, size)) { > + if (copy_from_user(copy, data, size) == size) { > kfree(copy); > return ERR_PTR(-EFAULT); > } > if (size != PAGE_SIZE) { > + WARN_ON(1); > if (copy_from_user(copy + size, data + size, PAGE_SIZE - size)) > memset(copy + size, 0, PAGE_SIZE - size); > } [...] Cheers ---Dave