From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x227NTW0uCt4cO8peob5UACwEnVXxgMbqYia4fmPPWdLEi1lsCnqGqDkQScm/sEUespsMp0Jd ARC-Seal: i=1; a=rsa-sha256; t=1517394484; cv=none; d=google.com; s=arc-20160816; b=RNlncl+KV/zLwvpVMSKzDrrnJspYnYz5I7/KH0GLNG8U7OphZjF3CHBG665r7Q4YIH j+UnmjrOG1sUkmX9aZfeq6doCMSQvKQTqPwxFNwnMvjZ9s3UZwSS54Jkp/j28RvJprcj uAD7Uhc00GhzS/7fjlKygjpd6n0IMekaoHklx7A5IOJxchCAxvUITLceth8RIesCsb8V 0nAvXjTx52vEcv3Onddb2nDsM8A/RXiMzhwycFbouh14z+aF7FZRSmEdkok04E/3ZRXo BRj8U8DEb3kT7GQLqCc3nK76BGPCYxR33JVcVlUOAyA+qmEUHyljougxq638JFyqBmrt MSUA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-transfer-encoding :content-disposition:mime-version:references:message-id:subject:cc :to:from:date:dkim-signature:arc-authentication-results; bh=1wUTnejcbn1io2ZCJthoY6tjZkiV0Mx/UcDnMDvRQw0=; b=vHTjZNzZNsIJpuE/uhahekMWlSCfSb6ZnItKiO91Z9+iLqyWCXEbLpBhweVbYhylVO St2P8ztc8qHIZ1XNVqtG8FBI4xaMBCaTUC6TcqCgklzuSGFMacjYPN26PAE0ctZ3Dm3/ kpQDCVNIIvUwDIc/BElJCLwrMC3kN6XIe4o/Bp/h+V6xpEHUzvyEUlEo6LdZdUAcoGZd UYwfj6rVT3cyNXz+CkpYCG6TXdx15nLaXscZzA0eM0+i2BIcYoxHn3Td7NAOU81uFehP wbWQiF4wlzN76J/vugUCWyuFVemUlD18e6ElG7FaldCfXak8DdXeBOFdcb2WsyPAjFVN b53A== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@infradead.org header.s=merlin.20170209 header.b=lHTaGIc+; spf=pass (google.com: best guess record for domain of peterz@infradead.org designates 205.233.59.134 as permitted sender) smtp.mailfrom=peterz@infradead.org Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=merlin.20170209 header.b=lHTaGIc+; spf=pass (google.com: best guess record for domain of peterz@infradead.org designates 205.233.59.134 as permitted sender) smtp.mailfrom=peterz@infradead.org Date: Wed, 31 Jan 2018 11:27:50 +0100 From: Peter Zijlstra To: David Woodhouse Cc: Josh Poimboeuf , Thomas Gleixner , linux-kernel@vger.kernel.org, Dave Hansen , Ashok Raj , Tim Chen , Andy Lutomirski , Linus Torvalds , Greg KH , Andrea Arcangeli , Andi Kleen , Arjan Van De Ven , Dan Williams , Paolo Bonzini , Jun Nakajima , Asit Mallick , Jason Baron Subject: Re: [PATCH 20/24] objtool: Another static block fail Message-ID: <20180131102750.GN2269@hirez.programming.kicks-ass.net> References: <20180123152539.374360046@infradead.org> <20180123152639.170696914@infradead.org> <20180129225252.bi2etgk3eqprcv3x@treble> <20180130095653.GZ2269@hirez.programming.kicks-ass.net> <20180131031221.7k2igskvrpsphc2u@treble> <20180131100119.GJ2269@hirez.programming.kicks-ass.net> <1517393226.18619.156.camel@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1517393226.18619.156.camel@infradead.org> User-Agent: Mutt/1.9.2 (2017-12-15) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590397857832042088?= X-GMAIL-MSGID: =?utf-8?q?1591103438838148267?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Wed, Jan 31, 2018 at 10:07:06AM +0000, David Woodhouse wrote: > On Wed, 2018-01-31 at 11:01 +0100, Peter Zijlstra wrote: > > On Tue, Jan 30, 2018 at 09:12:21PM -0600, Josh Poimboeuf wrote: > > >  > > > Or, maybe we should just forget the whole thing and just stick with the > > > dynamic IBRS checks with lfence.  Yes, it's less ideal for the kernel, > > > but adding these acrobatics to objtool also has a cost. > > > > For now, IBRS seems off the table entirely. But no, I really don't want > > to have to unconditionally eat the LFENCE cost in all those sites. > > There's also alternatives. And without the IBRS-on-kernel-entry bits > there aren't that many call sites that really need this anyway and > don't have *other* conditionals that really are runtime-only (like > dumpable etc.). There is that.. So I think people wanted to use jump_labels for IBRS so that we could runtime enable it when people loaded dodgy modules or something. But even that we could all write in inline asm if needed I suppose, it'll be ugly, but it should work.