From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id 14615280259 for ; Sun, 12 Nov 2017 22:52:57 -0500 (EST) Received: by mail-pf0-f197.google.com with SMTP id d28so13724583pfe.1 for ; Sun, 12 Nov 2017 19:52:57 -0800 (PST) Received: from mail.kernel.org (mail.kernel.org. [198.145.29.99]) by mx.google.com with ESMTPS id 132si3601711pga.176.2017.11.12.19.52.55 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 12 Nov 2017 19:52:55 -0800 (PST) Received: from mail-it0-f41.google.com (mail-it0-f41.google.com [209.85.214.41]) (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 537A121992 for ; Mon, 13 Nov 2017 03:52:55 +0000 (UTC) Received: by mail-it0-f41.google.com with SMTP id b5so1468143itc.3 for ; Sun, 12 Nov 2017 19:52:55 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <7ec56785-8e18-4ac8-ebe8-ebdd3ac265da@linux.intel.com> References: <20171108194646.907A1942@viggo.jf.intel.com> <20171108194731.AB5BDA01@viggo.jf.intel.com> <6871f284-b7e9-f843-608f-5345f9d03396@linux.intel.com> <27b55108-1e72-cb3d-d5d8-ffe0238245aa@linux.intel.com> <4c8c441e-d65c-fcec-7718-6997bd010971@linux.intel.com> <7ec56785-8e18-4ac8-ebe8-ebdd3ac265da@linux.intel.com> From: Andy Lutomirski Date: Sun, 12 Nov 2017 19:52:34 -0800 Message-ID: Subject: Re: [PATCH 24/30] x86, kaiser: disable native VSYSCALL Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: Andy Lutomirski , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , moritz.lipp@iaik.tugraz.at, Daniel Gruss , michael.schwarz@iaik.tugraz.at, richard.fellner@student.tugraz.at, Linus Torvalds , Kees Cook , Hugh Dickins , X86 ML On Fri, Nov 10, 2017 at 3:04 PM, Dave Hansen wrote: > On 11/10/2017 02:06 PM, Andy Lutomirski wrote: >> On Thu, Nov 9, 2017 at 10:31 PM, Dave Hansen >> wrote: >>> On 11/09/2017 06:25 PM, Andy Lutomirski wrote: >>>> Here are two proposals to address this without breaking vsyscalls. >>>> >>>> 1. Set NX on low mappings that are _PAGE_USER. Don't set NX on high >>>> mappings but, optionally, warn if you see _PAGE_USER on any address >>>> that isn't the vsyscall page. >>>> >>>> 2. Ignore _PAGE_USER entirely and just mark the EFI mm as special so >>>> KAISER doesn't muck with it. >>> >>> These are totally doable. But, what's the big deal with breaking native >>> vsyscall? We can still do the emulation so nothing breaks: it is just slow. >> >> I have nothing against disabling native. I object to breaking the >> weird binary tracing behavior in the emulation mode, especially if >> it's tangled up with KAISER. I got all kinds of flak in an earlier >> version of the vsyscall emulation patches when I broke that use case. >> KAISER may get very widely backported -- let's not make changes that >> are already known to break things. > > Is the thing that broke a "user mode program that actually looks at the > vsyscall page"? Like Linus is referring to here: > Yes. But I disagree with Linus. I think it would be perfectly reasonable to enable KAISER and to use a tool like pin on a legacy binary from some enterprise distribution. I bet there are lots of enterprise distributions that are still supported that use vsyscalls. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org