From patchwork Tue May 19 12:18:16 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Will Deacon X-Patchwork-Id: 11557533 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 06EED60D for ; Tue, 19 May 2020 12:18:44 +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 D02C72081A for ; Tue, 19 May 2020 12:18:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="EOxp306j"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="LyBClsw4" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D02C72081A 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=piiRzw1m/Zr41wlEQ2vd2L/66GbZY2EueipDQ/vBgJU=; b=EOxp306jeo1PdO AZVh4/V2oVDS8h5WH1SzUNlbikOkIWvBeyL+BAzdbz7Rc+qoMvFk4TKUfwldEAf7qMbIgqPm+3iy4 2UmGMijdcfmRRCfThk6AgN39LbZA3Izt/Q8TJOJqI5Q5bMFOjqZut54LwcBWGCgmhASsjb5aA+Kqq eaKnUatewo/nmv8TBmR1O9WgVujmRDo2HSKIdgY0qRn8yJws0VmVhDFo6R55fwUDYUHdFcpauom+V 3Db+sL56c2nJilfScuXT7VKcj9q6/BpjfBFr7B2MKxtTRz5owTe0BmG+srdoXe0L/jqa3T14Q7VfJ IcdWYqmQ7b+gc7+EuLaQ==; 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 1jb1Cg-0006YX-7J; Tue, 19 May 2020 12:18:38 +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 1jb1CT-0006Os-VQ for linux-arm-kernel@lists.infradead.org; Tue, 19 May 2020 12:18:27 +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 6BF4620829; Tue, 19 May 2020 12:18:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589890705; bh=bohwZM/RhHrUa6nQzL2fB7GJKIDKG8zmn0Lj5bpPW1g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=LyBClsw42IKLzE9/YoqNA2jlw4dAJ/dGFRpi/Do+R2lWKx9KLXrmJVPVGhCpXNjRG WTIly+od1nTaHVj0SqxgPqcwIqeNfsPOEK5YHFfFrnxt5QQo6wsjkeb1SZm/bJp04a qRym00p9T5Z/o3IqGxLV38MYkCciJLcbdUsLQGP4= From: Will Deacon To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 1/3] arm64: vdso: Don't prefix sigreturn trampoline with a BTI C instruction Date: Tue, 19 May 2020 13:18:16 +0100 Message-Id: <20200519121818.14511-2-will@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200519121818.14511-1-will@kernel.org> References: <20200519121818.14511-1-will@kernel.org> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200519_051826_026654_4DA78647 X-CRM114-Status: GOOD ( 10.67 ) 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 For better or worse, GDB relies on the exact instruction sequence in the VDSO sigreturn trampoline in order to unwind from signals correctly. Commit 714a8d02ca4d ("arm64: asm: Override SYM_FUNC_START when building the kernel with BTI") unfortunately added a BTI C instruction to the start of __kernel_rt_sigreturn, which breaks this check. Thankfully, it's also not required, since the trampoline is called from a RET instruction when returning from the signal handler Remove the unnecessary BTI C instruction from __kernel_rt_sigreturn. Cc: Dave Martin Cc: Mark Brown Cc: Daniel Kiss Cc: Tamas Zsoldos Fixes: 714a8d02ca4d ("arm64: asm: Override SYM_FUNC_START when building the kernel with BTI") Signed-off-by: Will Deacon --- arch/arm64/kernel/vdso/sigreturn.S | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kernel/vdso/sigreturn.S b/arch/arm64/kernel/vdso/sigreturn.S index 3fb13b81f780..83ac284dae79 100644 --- a/arch/arm64/kernel/vdso/sigreturn.S +++ b/arch/arm64/kernel/vdso/sigreturn.S @@ -15,7 +15,14 @@ .text nop -SYM_FUNC_START(__kernel_rt_sigreturn) +/* + * GDB relies on being able to identify the sigreturn instruction sequence to + * unwind from signal handlers. We cannot, therefore, use SYM_FUNC_START() + * here, as it will emit a BTI C instruction and break the unwinder. Thankfully, + * this function is only ever called from a RET and so omitting the landing pad + * is perfectly fine. + */ +SYM_START(__kernel_rt_sigreturn, SYM_L_GLOBAL, SYM_A_ALIGN) .cfi_startproc .cfi_signal_frame .cfi_def_cfa x29, 0