From patchwork Fri Aug 23 16:37:17 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Catalin Marinas X-Patchwork-Id: 11112079 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 667561709 for ; Fri, 23 Aug 2019 16:37:28 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3C9352339D for ; Fri, 23 Aug 2019 16:37:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3C9352339D 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 1F7506B04AD; Fri, 23 Aug 2019 12:37:26 -0400 (EDT) Delivered-To: linux-mm-outgoing@kvack.org Received: by kanga.kvack.org (Postfix, from userid 40) id 1A97D6B04AE; Fri, 23 Aug 2019 12:37:26 -0400 (EDT) X-Original-To: int-list-linux-mm@kvack.org X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0979D6B04AF; Fri, 23 Aug 2019 12:37:26 -0400 (EDT) X-Original-To: linux-mm@kvack.org X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0029.hostedemail.com [216.40.44.29]) by kanga.kvack.org (Postfix) with ESMTP id DFCB06B04AD for ; Fri, 23 Aug 2019 12:37:25 -0400 (EDT) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id A01E952A6 for ; Fri, 23 Aug 2019 16:37:25 +0000 (UTC) X-FDA: 75854248050.11.legs02_23b21bc3cfb63 X-Spam-Summary: 2,0,0,f12efc52109e01cb,d41d8cd98f00b204,catalin.marinas@arm.com,:linux-arm-kernel@lists.infradead.org::akpm@linux-foundation.org:vincenzo.frascino@arm.com:will@kernel.org:andreyknvl@google.com:szabolcs.nagy@arm.com:kevin.brodsky@arm.com:dave.martin@arm.com:dave.hansen@intel.com:linux-doc@vger.kernel.org:linux-arch@vger.kernel.org:will.deacon@arm.com,RULES_HIT:41:69:355:379:541:800:960:973:988:989:1260:1261:1311:1314:1345:1359:1431:1437:1515:1534:1543:1711:1730:1747:1777:1792:2393:2553:2559:2562:2693:2899:2907:3138:3139:3140:3141:3142:3354:3865:3866:3867:3868:3870:3871:3872:3874:4250:4321:5007:6119:6261:6742:7264:7576:7903:8634:8660:10004:11232:11473:11658:11914:12043:12297:12555:12679:12683:13148:13161:13229:13230:13894:14096:14181:14394:14721:21080:21230:21451:21627:21795:21796:21810:30003:30012:30036:30054:30055:30090,0,RBL:217.140.110.172:@arm.com:.lbl8.mailshell.net-62.2.0.100 64.100.201.201,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF :not bul X-HE-Tag: legs02_23b21bc3cfb63 X-Filterd-Recvd-Size: 4612 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf32.hostedemail.com (Postfix) with ESMTP for ; Fri, 23 Aug 2019 16:37:25 +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 44B021570; Fri, 23 Aug 2019 09:37:24 -0700 (PDT) Received: from arrakis.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 75CAC3F246; Fri, 23 Aug 2019 09:37:22 -0700 (PDT) From: Catalin Marinas To: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Cc: Andrew Morton , Vincenzo Frascino , Will Deacon , Andrey Konovalov , Szabolcs Nagy , Kevin Brodsky , Dave P Martin , Dave Hansen , linux-doc@vger.kernel.org, linux-arch@vger.kernel.org, Will Deacon Subject: [PATCH v10 1/1] arm64: Relax Documentation/arm64/tagged-pointers.rst Date: Fri, 23 Aug 2019 17:37:17 +0100 Message-Id: <20190823163717.19569-2-catalin.marinas@arm.com> X-Mailer: git-send-email 2.23.0.rc0 In-Reply-To: <20190823163717.19569-1-catalin.marinas@arm.com> References: <20190823163717.19569-1-catalin.marinas@arm.com> MIME-Version: 1.0 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: 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 | 21 ++++++++++++++------- 1 file changed, 14 insertions(+), 7 deletions(-) diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst index 2acdec3ebbeb..eab4323609b9 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 +63,9 @@ 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. + Other considerations --------------------