From patchwork Wed May 20 17:55:39 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Will Deacon X-Patchwork-Id: 11560961 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 0CA6560D for ; Wed, 20 May 2020 17:57:08 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id DD3FE204EF for ; Wed, 20 May 2020 17:57:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="GeBippdt"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="WIipLvnD" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DD3FE204EF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org 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=1Wm5aghybQF77mukVdMiaqser4QIYZOAE37apV83qMk=; b=GeBippdtzKpeYp 0PhXO5yO9tLnH4IWUTUc0XAirhajpKttKGM8gpHsFEo4IVCbeoUhg7CxuL4Blwj8sBGfkt1ovFotO F6d7sBzH6A48hmJS9yl8MGbx+ZrDRCi3LTfV6+LaITiPeQ8WCMOO4+vhO0YODyRdoRt006JkXPNsn FxEHw5BtZVWZysCS07tZIE0Dhqk8CZgxD4Nk13ASji5eZrSzMM0zxnjNo6uf0dABIcCjdQfp3gCHr ZyQPedQt4790jnAFX5x6MMca4ED4SuKhfE6ByMHvCTw4Jt8SGrLt7SJ6PieoZvYgOLC4BMLHZPm9s +mXlJF5KwiaPZ3rigO6Q==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jbSxg-00046N-Vn; Wed, 20 May 2020 17:57:00 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jbSwX-0003E1-2S for linux-arm-kernel@lists.infradead.org; Wed, 20 May 2020 17:55:50 +0000 Received: from localhost.localdomain (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 605C4207D8; Wed, 20 May 2020 17:55:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589997348; bh=SruxTR6nMHhaDx6eZgigCukwq995Dww7NLTW7ti7KC0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=WIipLvnD2T0Og4Qns/pRRNf7HJCsIoIhmiNLZgTqER6X29KDbDwuX2Y1kJV4va9cC PPAMjstRWBkI5uauCPBzJkoYZessXDWugNWfbQIaW7eNHYb7+SfTHhs9yAvPiPDabJ +qems5oOuxpWRNYoKgyB/LXEa8+pgflHg6/F/e/A= From: Will Deacon To: linux-arm-kernel@lists.infradead.org Subject: [PATCH v3 2/2] arm64: vdso: Fix CFI directives in sigreturn trampoline Date: Wed, 20 May 2020 18:55:39 +0100 Message-Id: <20200520175539.28464-3-will@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200520175539.28464-1-will@kernel.org> References: <20200520175539.28464-1-will@kernel.org> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200520_105549_182440_101F500A X-CRM114-Status: GOOD ( 15.63 ) X-Spam-Score: -5.2 (-----) X-Spam-Report: SpamAssassin version 3.4.4 on bombadil.infradead.org summary: Content analysis details: (-5.2 points) pts rule name description ---- ---------------------- -------------------------------------------------- -5.0 RCVD_IN_DNSWL_HI RBL: Sender listed at https://www.dnswl.org/, high trust [198.145.29.99 listed in list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature -0.0 DKIMWL_WL_HIGH DKIMwl.org - Whitelisted High sender 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: Will Deacon , Tamas Zsoldos , Mark Brown , kernel-team@android.com, Dave Martin , Daniel Kiss Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org Daniel reports that the .cfi_startproc is misplaced for the sigreturn trampoline, which causes LLVM's unwinder to misbehave: | I run into this with LLVM’s unwinder. | This combination was always broken. This prompted Dave to question our use of CFI directives more generally, and I ended up going down a rabbit hole trying to figure out how this very poorly documented stuff gets used. Move the CFI directives so that the "mysterious NOP" is included in the .cfi_{start,end}proc block and add a bunch of comments so that I can save myself another headache in future. Cc: Tamas Zsoldos Reported-by: Dave Martin Reported-by: Daniel Kiss Signed-off-by: Will Deacon --- arch/arm64/kernel/vdso/sigreturn.S | 44 +++++++++++++++++++++++----- arch/arm64/kernel/vdso32/sigreturn.S | 3 ++ 2 files changed, 40 insertions(+), 7 deletions(-) diff --git a/arch/arm64/kernel/vdso/sigreturn.S b/arch/arm64/kernel/vdso/sigreturn.S index 0c921130002a..620a3ef837b7 100644 --- a/arch/arm64/kernel/vdso/sigreturn.S +++ b/arch/arm64/kernel/vdso/sigreturn.S @@ -1,7 +1,11 @@ /* SPDX-License-Identifier: GPL-2.0-only */ /* * Sigreturn trampoline for returning from a signal when the SA_RESTORER - * flag is not set. + * flag is not set. It serves primarily as a hall of shame for crappy + * unwinders and features an exciting but mysterious NOP instruction. + * + * It's also fragile as hell, so please think twice before changing anything + * in here. * * Copyright (C) 2012 ARM Limited * @@ -14,7 +18,38 @@ .text - nop +/* Ensure that the mysterious NOP can be associated with a function. */ + .cfi_startproc + +/* + * .cfi_signal_frame causes the corresponding Frame Description Entry in the + * .eh_frame section to be annotated as a signal frame. This allows DWARF + * unwinders (e.g. libstdc++) to implement _Unwind_GetIPInfo(), which permits + * unwinding out of the signal trampoline without the need for the mysterious + * NOP. + */ + .cfi_signal_frame + +/* + * Tell the unwinder where to locate the frame record linking back to the + * interrupted context. We don't provide unwind info for registers other + * than the frame pointer and the link register here; in practice, this + * is sufficient for unwinding in C/C++ based runtimes and the values in + * the sigcontext may have been modified by this point anyway. Debuggers + * already have baked-in strategies for attempting to unwind out of signals. + */ + .cfi_def_cfa x29, 0 + .cfi_offset x29, 0 * 8 + .cfi_offset x30, 1 * 8 + +/* + * This mysterious NOP is required for some unwinders (e.g. libc++) that + * unconditionally subtract one from the result of _Unwind_GetIP() in order to + * identify the calling function. + * Hack borrowed from arch/powerpc/kernel/vdso64/sigtramp.S. + */ + nop // Mysterious NOP + /* * GDB relies on being able to identify the sigreturn instruction sequence to * unwind from signal handlers. We cannot, therefore, use SYM_FUNC_START() @@ -23,11 +58,6 @@ * is perfectly fine. */ SYM_CODE_START(__kernel_rt_sigreturn) - .cfi_startproc - .cfi_signal_frame - .cfi_def_cfa x29, 0 - .cfi_offset x29, 0 * 8 - .cfi_offset x30, 1 * 8 mov x8, #__NR_rt_sigreturn svc #0 .cfi_endproc diff --git a/arch/arm64/kernel/vdso32/sigreturn.S b/arch/arm64/kernel/vdso32/sigreturn.S index b36d4e2267a3..b0091064c3d6 100644 --- a/arch/arm64/kernel/vdso32/sigreturn.S +++ b/arch/arm64/kernel/vdso32/sigreturn.S @@ -3,6 +3,9 @@ * This file provides both A32 and T32 versions, in accordance with the * arm sigreturn code. * + * Please read the comments in arch/arm64/kernel/vdso/sigreturn.S to + * understand some of the craziness in here. + * * Copyright (C) 2018 ARM Limited */