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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=no 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 49C4DC433E0 for ; Tue, 19 May 2020 15:26:52 +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 1BF222075F for ; Tue, 19 May 2020 15:26:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="fB1qP14J"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="c0XU5M4q" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1BF222075F 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+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=DnOmKHLFbFUevTHSKYn1jcWdFZU/oGWBhi0eg4YNcyQ=; b=fB1qP14JLraVFi XBmN/WJyGO9GB+sxefjxt7geeCIjSJIVoKqZyQhPGoAxSv8GDfjZERqSrmBgzJWHHs3OUYBo4/vBI oX/042L6eRfDwp2NsOwtqCcmjDJ+rOAz0cf4hyTaTBjj9V52QmMvLi9oaEYEwp8OrSOsqjyWF6NRa KazGEVeJZXshn7xcsvvyrJCAjkdyqbbz8LXddnrwJ+gQEJsPmWBnwtaiBf4o6RQ48LwNPIvC6aiTK +XYLcckWr2av5YH2BszgCkq3Hx46SFEBRsc+R51k+eCGjGoFhu865ojiwMdPGmOlVawyUPS/N/jhZ IGki45DPTlXIk5yENFSA==; 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 1jb48i-0002JM-Vt; Tue, 19 May 2020 15:26:44 +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 1jb48g-0002J1-32 for linux-arm-kernel@lists.infradead.org; Tue, 19 May 2020 15:26:43 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A6C742075F; Tue, 19 May 2020 15:26:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589902001; bh=8vQcrAtboUpyrk0w+y/s5khTeXHH32xrzsWg2Hqy7u4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=c0XU5M4qhlfHjCcQ4nlTxmUxk3uhRGg2aBO/MVtb87KSfU0OsTyslKAvNFD4O9Udl g7htGdpZlFGjO+ESIvHIKJ8bTy5F4m1vkAFd1G02WjrE54DVn95ZOm4dxXsdrtcxj8 e/bTggctDl6aH6b8EyA0i+t06f2oxXZD9kLqXjdA= Date: Tue, 19 May 2020 16:26:37 +0100 From: Will Deacon To: Mark Brown Subject: Re: [PATCH 1/3] arm64: vdso: Don't prefix sigreturn trampoline with a BTI C instruction Message-ID: <20200519152637.GB15811@willie-the-truck> References: <20200519121818.14511-1-will@kernel.org> <20200519121818.14511-2-will@kernel.org> <20200519123843.GJ4611@sirena.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200519123843.GJ4611@sirena.org.uk> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200519_082642_149221_F1320C37 X-CRM114-Status: GOOD ( 17.37 ) 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 , kernel-team@android.com, Dave Martin , 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 01:38:43PM +0100, Mark Brown wrote: > On Tue, May 19, 2020 at 01:18:16PM +0100, Will Deacon wrote: > > > Fixes: 714a8d02ca4d ("arm64: asm: Override SYM_FUNC_START when building the kernel with BTI") > > I'd say it's the annotation conversion not this, and also that the > bikeshed would be most fetching in orange. > > c91db232da484851 (arm64: vdso: Convert to modern assembler annotations) I initially had both, but that felt weird so I dropped this one. However, I'm happy to switch it for v2. > > -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) > > Shouldn't this be a SYM_CODE_START()? It's the same thing as above > currently and we'll break an awful lot more if we change what it does in > a way that affects the code, plus the use of CODE basically says the > above - it's a "this is non-standard and we know exactly what we're > doing, don't mess with it" annotation. If not then it'd be good to > cover that in the comment since otherwise this seems like it's asking > for a cleanup, we shouldn't really have raw SYM_START() in code. > > I guess we also ought to annotate the 32 bit sigreturns as CODE too, > though it's academic there without BTI. Yes, that's much better, I'll use SYM_CODE_START() and update the compat code too (I'd forgotten it wasn't an array of hex anymore). Thanks, Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel