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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 41929C3A59E for ; Wed, 21 Aug 2019 17:34:01 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 025022332A for ; Wed, 21 Aug 2019 17:34:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="egpMmbAI" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 025022332A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 892046B032A; Wed, 21 Aug 2019 13:34:00 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 842F86B032B; Wed, 21 Aug 2019 13:34:00 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 731526B032C; Wed, 21 Aug 2019 13:34:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0056.hostedemail.com [216.40.44.56]) by kanga.kvack.org (Postfix) with ESMTP id 537A06B032A for ; Wed, 21 Aug 2019 13:34:00 -0400 (EDT) Received: from smtpin18.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with SMTP id 0537B8248AB9 for ; Wed, 21 Aug 2019 17:34:00 +0000 (UTC) X-FDA: 75847132998.18.shape73_7a298b2a3104d X-HE-Tag: shape73_7a298b2a3104d X-Filterd-Recvd-Size: 5737 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf07.hostedemail.com (Postfix) with ESMTP for ; Wed, 21 Aug 2019 17:33:59 +0000 (UTC) Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 191AC22D6D; Wed, 21 Aug 2019 17:33:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1566408838; bh=bs8hczsNPANODvH4KyJJB3Ke129MTzcBxY5ubZQ+el4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=egpMmbAIpi3WaaAuHcdz1N5cHHlhmeIXdbl9GEwrlxmRauiS3jNUVkRBTETUsH+62 eSLY/o1hrwQabl6eUuj5QKiuAKqdZQkPK5Tao3iNY/v1WtQLL+6CwMcB1l9FuEE3sp jAAGjQBiyoEh2qOZNuyopa5G+CsiudEpVo1ttDpA= Date: Wed, 21 Aug 2019 18:33:53 +0100 From: Will Deacon To: Catalin Marinas Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, Andrew Morton , Vincenzo Frascino , Andrey Konovalov , Szabolcs Nagy , Kevin Brodsky , Dave P Martin , Dave Hansen , linux-doc@vger.kernel.org, linux-arch@vger.kernel.org, Will Deacon Subject: Re: [PATCH v9 3/3] arm64: Relax Documentation/arm64/tagged-pointers.rst Message-ID: <20190821173352.yqfgaozi7nfhcofg@willie-the-truck> References: <20190821164730.47450-1-catalin.marinas@arm.com> <20190821164730.47450-4-catalin.marinas@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190821164730.47450-4-catalin.marinas@arm.com> User-Agent: NeoMutt/20170113 (1.7.2) 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, Aug 21, 2019 at 05:47:30PM +0100, Catalin Marinas wrote: > From: Vincenzo Frascino > > On AArch64 the TCR_EL1.TBI0 bit is set by default, allowing userspace > (EL0) to perform memory accesses through 64-bit pointers with a non-zero > top byte. However, such pointers were not allowed at the user-kernel > syscall ABI boundary. > > With the Tagged Address ABI patchset, it is now possible to pass tagged > pointers to the syscalls. Relax the requirements described in > tagged-pointers.rst to be compliant with the behaviours guaranteed by > the AArch64 Tagged Address ABI. > > Cc: Will Deacon > Cc: Szabolcs Nagy > Cc: Kevin Brodsky > Acked-by: Andrey Konovalov > Signed-off-by: Vincenzo Frascino > Co-developed-by: Catalin Marinas > Signed-off-by: Catalin Marinas > --- > Documentation/arm64/tagged-pointers.rst | 23 ++++++++++++++++------- > 1 file changed, 16 insertions(+), 7 deletions(-) > > diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst > index 2acdec3ebbeb..04f2ba9b779e 100644 > --- a/Documentation/arm64/tagged-pointers.rst > +++ b/Documentation/arm64/tagged-pointers.rst > @@ -20,7 +20,9 @@ Passing tagged addresses to the kernel > -------------------------------------- > > All interpretation of userspace memory addresses by the kernel assumes > -an address tag of 0x00. > +an address tag of 0x00, unless the application enables the AArch64 > +Tagged Address ABI explicitly > +(Documentation/arm64/tagged-address-abi.rst). > > This includes, but is not limited to, addresses found in: > > @@ -33,13 +35,15 @@ This includes, but is not limited to, addresses found in: > - the frame pointer (x29) and frame records, e.g. when interpreting > them to generate a backtrace or call graph. > > -Using non-zero address tags in any of these locations may result in an > -error code being returned, a (fatal) signal being raised, or other modes > -of failure. > +Using non-zero address tags in any of these locations when the > +userspace application did not enable the AArch64 Tagged Address ABI may > +result in an error code being returned, a (fatal) signal being raised, > +or other modes of failure. > > -For these reasons, passing non-zero address tags to the kernel via > -system calls is forbidden, and using a non-zero address tag for sp is > -strongly discouraged. > +For these reasons, when the AArch64 Tagged Address ABI is disabled, > +passing non-zero address tags to the kernel via system calls is > +forbidden, and using a non-zero address tag for sp is strongly > +discouraged. > > Programs maintaining a frame pointer and frame records that use non-zero > address tags may suffer impaired or inaccurate debug and profiling > @@ -59,6 +63,11 @@ be preserved. > The architecture prevents the use of a tagged PC, so the upper byte will > be set to a sign-extension of bit 55 on exception return. > > +This behaviour is maintained when the AArch64 Tagged Address ABI is > +enabled. In addition, with the exceptions above, the kernel will > +preserve any non-zero tags passed by the user via syscalls and stored in > +kernel data structures (e.g. ``set_robust_list()``, ``sigaltstack()``). Hmm. I can see the need to provide this guarantee for things like set_robust_list(), but the problem is that the statement above is too broad and isn't strictly true: for example, mmap() doesn't propagate the tag of its address parameter into the VMA. So I think we need to nail this down a bit more, but I'm having a really hard time coming up with some wording :( Will