From patchwork Wed Jun 12 14:21:10 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vincenzo Frascino X-Patchwork-Id: 10990099 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id CF61014BB for ; Wed, 12 Jun 2019 14:21:37 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C01EE2891B for ; Wed, 12 Jun 2019 14:21:37 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B3D7928571; Wed, 12 Jun 2019 14:21:37 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 3699F288FC for ; Wed, 12 Jun 2019 14:21:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2409286AbfFLOV2 (ORCPT ); Wed, 12 Jun 2019 10:21:28 -0400 Received: from foss.arm.com ([217.140.110.172]:53922 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2409269AbfFLOV2 (ORCPT ); Wed, 12 Jun 2019 10:21:28 -0400 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 6C827337; Wed, 12 Jun 2019 07:21:27 -0700 (PDT) Received: from e119884-lin.cambridge.arm.com (e119884-lin.cambridge.arm.com [10.1.196.72]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 184D13F557; Wed, 12 Jun 2019 07:21:25 -0700 (PDT) From: Vincenzo Frascino To: linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Catalin Marinas , Will Deacon , Andrey Konovalov , Alexander Viro Subject: [PATCH v4 1/2] arm64: Define Documentation/arm64/tagged-address-abi.txt Date: Wed, 12 Jun 2019 15:21:10 +0100 Message-Id: <20190612142111.28161-2-vincenzo.frascino@arm.com> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190612142111.28161-1-vincenzo.frascino@arm.com> References: <20190612142111.28161-1-vincenzo.frascino@arm.com> MIME-Version: 1.0 Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On arm64 the TCR_EL1.TBI0 bit has been always enabled hence the userspace (EL0) is allowed to set a non-zero value in the top byte but the resulting pointers are not allowed at the user-kernel syscall ABI boundary. With the relaxed ABI proposed through this document, it is now possible to pass tagged pointers to the syscalls, when these pointers are in memory ranges obtained by an anonymous (MAP_ANONYMOUS) mmap(). This change in the ABI requires a mechanism to requires the userspace to opt-in to such an option. Specify and document the way in which sysctl and prctl() can be used in combination to allow the userspace to opt-in this feature. Cc: Catalin Marinas Cc: Will Deacon CC: Andrey Konovalov Signed-off-by: Vincenzo Frascino --- Documentation/arm64/tagged-address-abi.txt | 111 +++++++++++++++++++++ 1 file changed, 111 insertions(+) create mode 100644 Documentation/arm64/tagged-address-abi.txt diff --git a/Documentation/arm64/tagged-address-abi.txt b/Documentation/arm64/tagged-address-abi.txt new file mode 100644 index 000000000000..96e149e2c55c --- /dev/null +++ b/Documentation/arm64/tagged-address-abi.txt @@ -0,0 +1,111 @@ +ARM64 TAGGED ADDRESS ABI +======================== + +This document describes the usage and semantics of the Tagged Address +ABI on arm64. + +1. Introduction +--------------- + +On arm64 the TCR_EL1.TBI0 bit has been always enabled on the arm64 kernel, +hence the userspace (EL0) is allowed to set a non-zero value in the top +byte but the resulting pointers are not allowed at the user-kernel syscall +ABI boundary. + +This document describes a relaxation of the ABI with which it is possible +to pass tagged tagged pointers to the syscalls, when these pointers are in +memory ranges obtained as described in paragraph 2. + +Since it is not desirable to relax the ABI to allow tagged user addresses +into the kernel indiscriminately, arm64 provides a new sysctl interface +(/proc/sys/abi/tagged_addr) that is used to prevent the applications from +enabling the relaxed ABI and a new prctl() interface that can be used to +enable or disable the relaxed ABI. + +The sysctl is meant also for testing purposes in order to provide a simple +way for the userspace to verify the return error checking of the prctl() +command without having to reconfigure the kernel. + +The ABI properties are inherited by threads of the same application and +fork()'ed children but cleared when a new process is spawn (execve()). + +2. ARM64 Tagged Address ABI +--------------------------- + +From the kernel syscall interface prospective, we define, for the purposes +of this document, a "valid tagged pointer" as a pointer that either it has +a zero value set in the top byte or it has a non-zero value, it is in memory +ranges privately owned by a userspace process and it is obtained in one of +the following ways: + - mmap() done by the process itself, where either: + * flags = MAP_PRIVATE | MAP_ANONYMOUS + * flags = MAP_PRIVATE and the file descriptor refers to a regular + file or "/dev/zero" + - a mapping below sbrk(0) done by the process itself + - any memory mapped by the kernel in the process's address space during + creation and following the restrictions presented above (i.e. data, bss, + stack). + +The ARM64 Tagged Address ABI is an opt-in feature, and an application can +control it using the following prctl()s: + - PR_SET_TAGGED_ADDR_CTRL: can be used to enable the Tagged Address ABI. + - PR_GET_TAGGED_ADDR_CTRL: can be used to check the status of the Tagged + Address ABI. + +As a consequence of invoking PR_SET_TAGGED_ADDR_CTRL prctl() by an applications, +the ABI guarantees the following behaviours: + + - Every current or newly introduced syscall can accept any valid tagged + pointers. + + - If a non valid tagged pointer is passed to a syscall then the behaviour + is undefined. + + - Every valid tagged pointer is expected to work as an untagged one. + + - The kernel preserves any valid tagged pointers and returns them to the + userspace unchanged in all the cases except the ones documented in the + "Preserving tags" paragraph of tagged-pointers.txt. + +A definition of the meaning of tagged pointers on arm64 can be found in: +Documentation/arm64/tagged-pointers.txt. + +3. ARM64 Tagged Address ABI Exceptions +-------------------------------------- + +The behaviours described in paragraph 2, with particular reference to the +acceptance by the syscalls of any valid tagged pointer are not applicable +to the following cases: + - mmap() addr parameter. + - mremap() new_address parameter. + - prctl_set_mm() struct prctl_map fields. + - prctl_set_mm_map() struct prctl_map fields. + +4. Example of correct usage +--------------------------- + +void main(void) +{ + static int tbi_enabled = 0; + unsigned long tag = 0; + + char *ptr = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE, + MAP_ANONYMOUS, -1, 0); + + if (prctl(PR_SET_TAGGED_ADDR_CTRL, PR_TAGGED_ADDR_ENABLE, + 0, 0, 0) == 0) + tbi_enabled = 1; + + if (!ptr) + return -1; + + if (tbi_enabled) + tag = rand() & 0xff; + + ptr = (char *)((unsigned long)ptr | (tag << TAG_SHIFT)); + + *ptr = 'a'; + + ... +} + From patchwork Wed Jun 12 14:21:11 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vincenzo Frascino X-Patchwork-Id: 10990097 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id EA88214BB for ; Wed, 12 Jun 2019 14:21:36 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id DBE092817F for ; Wed, 12 Jun 2019 14:21:36 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id CF4C4287BB; Wed, 12 Jun 2019 14:21:36 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6B0DF28791 for ; Wed, 12 Jun 2019 14:21:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2409269AbfFLOVb (ORCPT ); Wed, 12 Jun 2019 10:21:31 -0400 Received: from foss.arm.com ([217.140.110.172]:53934 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2409290AbfFLOV3 (ORCPT ); Wed, 12 Jun 2019 10:21:29 -0400 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 03225A78; Wed, 12 Jun 2019 07:21:29 -0700 (PDT) Received: from e119884-lin.cambridge.arm.com (e119884-lin.cambridge.arm.com [10.1.196.72]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A12863F557; Wed, 12 Jun 2019 07:21:27 -0700 (PDT) From: Vincenzo Frascino To: linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Catalin Marinas , Will Deacon , Andrey Konovalov , Alexander Viro Subject: [PATCH v4 2/2] arm64: Relax Documentation/arm64/tagged-pointers.txt Date: Wed, 12 Jun 2019 15:21:11 +0100 Message-Id: <20190612142111.28161-3-vincenzo.frascino@arm.com> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190612142111.28161-1-vincenzo.frascino@arm.com> References: <20190612142111.28161-1-vincenzo.frascino@arm.com> MIME-Version: 1.0 Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On arm64 the TCR_EL1.TBI0 bit has been always enabled hence the userspace (EL0) is allowed to set a non-zero value in the top byte but the resulting pointers are not allowed at the user-kernel syscall ABI boundary. With the relaxed ABI proposed in this set, it is now possible to pass tagged pointers to the syscalls, when these pointers are in memory ranges obtained by an anonymous (MAP_ANONYMOUS) mmap(). Relax the requirements described in tagged-pointers.txt to be compliant with the behaviours guaranteed by the ARM64 Tagged Address ABI. Cc: Catalin Marinas Cc: Will Deacon CC: Andrey Konovalov Signed-off-by: Vincenzo Frascino --- Documentation/arm64/tagged-pointers.txt | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-) diff --git a/Documentation/arm64/tagged-pointers.txt b/Documentation/arm64/tagged-pointers.txt index a25a99e82bb1..db58a7e95805 100644 --- a/Documentation/arm64/tagged-pointers.txt +++ b/Documentation/arm64/tagged-pointers.txt @@ -18,7 +18,8 @@ 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 userspace opts-in the ARM64 Tagged +Address ABI via the PR_SET_TAGGED_ADDR_CTRL prctl(). This includes, but is not limited to, addresses found in: @@ -31,18 +32,23 @@ 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 opt-in to the ARM64 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 userspace application did not opt-in, 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 visibility. +A definition of the meaning of ARM64 Tagged Address ABI and of the +guarantees that the ABI provides when the userspace opts-in via prctl() +can be found in: Documentation/arm64/tagged-address-abi.txt. + Preserving tags --------------- @@ -57,6 +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 behaviours are preserved even when the the userspace opts-in the ARM64 +Tagged Address ABI via the PR_SET_TAGGED_ADDR_CTRL prctl(). + Other considerations --------------------