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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,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 657F9C433DF for ; Tue, 19 May 2020 13:25:46 +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 28872206BE for ; Tue, 19 May 2020 13:25:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="kKIeP21S" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 28872206BE 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=WFLPPR1/oC8bSfil/mohAmZvGeREym9VPynzpucbhR8=; b=kKIeP21SHgwTmn XCzn47lxcnsAGEb0Ht1AkCaQpLmlBKzb3QA2tu5Xc20e/Te5ZUjp7TM9CkYB/actWzV49O3yrVFua ODsuNi+StMdx1wki9+kdi1ageffYCkvmdC7y7GN60hyniC5CE6cumXQqdf8RFZPsXVjjRmtMMA8up Wpm1e5EPmyWd/c0sTTJX1OmY45UP0eF+kh0YlSZkD7kjPhnGALwMcuQ2LBT83DHkoS72c3Xt2dbIF w4n4Myxki9cldCaP8zNcU3bA3Bw0YFbbD7p7OtIkgeE7Scetg80mwuQ6gVDFTpLFac9GiiWFDf29o 9yMh+A6J7QgTujrnqejw==; 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 1jb2Fd-0006f2-Mh; Tue, 19 May 2020 13:25:45 +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 1jb2Fa-0006eQ-MZ for linux-arm-kernel@lists.infradead.org; Tue, 19 May 2020 13:25:44 +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 D47D530E; Tue, 19 May 2020 06:25:41 -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 EE0F23F52E; Tue, 19 May 2020 06:25:40 -0700 (PDT) Date: Tue, 19 May 2020 14:25:38 +0100 From: Dave Martin To: Mark Brown Subject: Re: [PATCH 1/3] arm64: vdso: Don't prefix sigreturn trampoline with a BTI C instruction Message-ID: <20200519132538.GE5031@arm.com> 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/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200519_062542_783186_E9E3034E X-CRM114-Status: GOOD ( 17.60 ) 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, Will Deacon , 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) > > > -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. Relating to this, we explicitly don't support calls to __kernel_rt_sigreturn. Rather, the "ret lr" that jumps here is supposed to be authenticated via pointer auth in the caller. If BTI {nothing} allows this while disallowing all BR/BLR then we could use that (I can't remember what BTI {nothing} is useful for, if anything). Otherwise, it's less clear what we should have here. Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel