From patchwork Thu Jul 25 13:50:44 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vincenzo Frascino X-Patchwork-Id: 11058889 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 D58E0746 for ; Thu, 25 Jul 2019 13:51:59 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C57D4286E2 for ; Thu, 25 Jul 2019 13:51:59 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B69FF28746; Thu, 25 Jul 2019 13:51:59 +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=-5.2 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED autolearn=unavailable version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 579FA28845 for ; Thu, 25 Jul 2019 13:51:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=wZuqghnPjqG5WL4LcslAKNS9O/RB6T3/3RunPmBLv2w=; b=iIJvsdUtAiOhpt qU+SqDglBWgd9CykWssDdg+K4/FaFDV9GmimsMOaWCyQSkk+6MMCT1S4qY1tQ9HCiKSJiM5wezgWq WOPNVLZwvHxF2EZOM3Hku1FtgYeZ/QxM/dITu4Gy3IDHLeKC8pb/DpLviC0EDKdEmLyIG37j66g/T PTv4I6ZfIKCf9YqrRURJTP3aaKw3xklUtCtPiBZmjrmmrDckBdzGEvuCaVNsyXwSR4uv7TtfkH+HX yaFq42zlJwfMWDy/8iB2PEnvq5Doq1JyFGGAXC1vXFf6ipxlLYBAyfYmOp+x/CYVOMvUrpvHJ4MsW AHwRJrNSeTtFh+VebWaw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hqe9w-0007Ha-TL; Thu, 25 Jul 2019 13:51:52 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hqe9M-0006hv-PA for linux-arm-kernel@lists.infradead.org; Thu, 25 Jul 2019 13:51:18 +0000 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 287B31595; Thu, 25 Jul 2019 06:51:16 -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 AE0983F71F; Thu, 25 Jul 2019 06:51:14 -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 Subject: [PATCH v6 2/2] arm64: Relax Documentation/arm64/tagged-pointers.rst Date: Thu, 25 Jul 2019 14:50:44 +0100 Message-Id: <20190725135044.24381-3-vincenzo.frascino@arm.com> X-Mailer: git-send-email 2.22.0 In-Reply-To: <20190725135044.24381-1-vincenzo.frascino@arm.com> References: <20190725135044.24381-1-vincenzo.frascino@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190725_065116_904789_42D31E13 X-CRM114-Status: GOOD ( 12.68 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Szabolcs Nagy , Catalin Marinas , vincenzo.frascino@arm.com, Will Deacon , Andrey Konovalov Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.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.rst 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 Acked-by: Szabolcs Nagy --- 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..933aaef8d52f 100644 --- a/Documentation/arm64/tagged-pointers.rst +++ b/Documentation/arm64/tagged-pointers.rst @@ -20,7 +20,8 @@ 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: @@ -33,18 +34,23 @@ 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.rst. + Preserving tags --------------- @@ -59,6 +65,9 @@ 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. +These behaviours are preserved even when the userspace opts-in to the ARM64 +Tagged Address ABI via the PR_SET_TAGGED_ADDR_CTRL prctl(). + Other considerations --------------------