From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AAF78C433DF for ; Tue, 19 May 2020 13:21:12 +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 54FF7204EA for ; Tue, 19 May 2020 13:21:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="u7IOjFAa" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 54FF7204EA Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.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:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=vRO+SPXTDGcY6TKDh6JyEn9ZcuwFBKCmJbterx2zC2s=; b=u7IOjFAaTbnJo1 oNt0LdBwn19gpQH+ZvdtH/v7hExgFDbGkGLBlpNGkZZVprQkH8O4Yr9La365tWTlCEFdlydZXfMu5 kBhrx+9i/TOnZLS8b4k5tNQYXw1RMFwNTYMJxY6emB8sEKqvKPEY55xoqwuncTuUNfCwkZigOjIqH 39Bh8Hmu+zh+UJLiHld5a++CO02X1vyDkShJLC8SgI7LpNyQhKt0qzEM4J4oRdMYUKZIo/ukXyXea OfDrRJrMzCye2XKp7/TTyydgy/9HavXgiZ8jxPJxvb/Sr5LA05v7t3+yfBOycuOz5Uf/R/wrOeIMb P+LZRBNjP4B5sNAAbUSw==; 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 1jb2BC-0003EP-WA; Tue, 19 May 2020 13:21:11 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jb2B9-0003Df-K9 for linux-arm-kernel@lists.infradead.org; Tue, 19 May 2020 13:21:09 +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 4EE5530E; Tue, 19 May 2020 06:21:04 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 685D73F52E; Tue, 19 May 2020 06:21:03 -0700 (PDT) Date: Tue, 19 May 2020 14:21:01 +0100 From: Dave Martin To: Will Deacon Subject: Re: [PATCH 1/3] arm64: vdso: Don't prefix sigreturn trampoline with a BTI C instruction Message-ID: <20200519132100.GD5031@arm.com> References: <20200519121818.14511-1-will@kernel.org> <20200519121818.14511-2-will@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200519121818.14511-2-will@kernel.org> User-Agent: Mutt/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200519_062107_705638_E28850C8 X-CRM114-Status: GOOD ( 17.49 ) 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: Tamas Zsoldos , Mark Brown , kernel-team@android.com, linux-arm-kernel@lists.infradead.org, Daniel Kiss Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, May 19, 2020 at 01:18:16PM +0100, Will Deacon wrote: > For better or worse, GDB relies on the exact instruction sequence in the > VDSO sigreturn trampoline in order to unwind from signals correctly. Are you sure? I'm struggling to find the relevant code in gdb. > 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 > -- > 2.26.2.761.g0e0b3e54be-goog > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel