Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756579AbdCUGq2 (ORCPT ); Tue, 21 Mar 2017 02:46:28 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:35478 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756426AbdCUGq1 (ORCPT ); Tue, 21 Mar 2017 02:46:27 -0400 Date: Tue, 21 Mar 2017 07:45:39 +0100 From: Ingo Molnar To: Andrei Vagin Cc: Ingo Molnar , Thomas Gleixner , LKML , Dmitry Safonov , Cyrill Gorcunov , Adam Borowski , Andy Lutomirski , Thomas Garnier , "H. Peter Anvin" Subject: Re: linux-next: x86: Unalbe to run x32 processes on the x86_64 kernel Message-ID: <20170321064539.GB30094@gmail.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4766 Lines: 118 * Andrei Vagin wrote: > Here is my bisect log: > [avagin@laptop linux-next]$ git bisect log > # bad: [f921b263d9602fb7873710c2df70671f2ffcf658] Add linux-next > specific files for 20170320 > # good: [4495c08e84729385774601b5146d51d9e5849f81] Linux 4.11-rc2 > git bisect start 'HEAD' 'v4.11-rc2' > # good: [adeec71e7b8a11ff44103cfa4e1c6002c27ae9ac] Merge > remote-tracking branch 'drm/drm-next' > git bisect good adeec71e7b8a11ff44103cfa4e1c6002c27ae9ac > # bad: [e5b1cee1bb9d8a66b28d64db9d8250ae2b0803d2] Merge > remote-tracking branch 'tty/tty-next' > git bisect bad e5b1cee1bb9d8a66b28d64db9d8250ae2b0803d2 > # good: [81cde6aecf21113c6bc65bc944587db4cbd3f64d] Merge > remote-tracking branch 'mmc/next' > git bisect good 81cde6aecf21113c6bc65bc944587db4cbd3f64d > # bad: [69d76288005784205678520826a74c28e49a1703] Merge > remote-tracking branch 'tip/auto-latest' > git bisect bad 69d76288005784205678520826a74c28e49a1703 > # good: [6d32edf2be6c4e0f08b102e2d3227278ebb477c9] Merge > remote-tracking branch 'spi/for-next' > git bisect good 6d32edf2be6c4e0f08b102e2d3227278ebb477c9 > # good: [61f63e383784bd0ab6529cfc95ddc59c713afcc9] Merge tag > 'perf-core-for-mingo-4.12-20170316' of > git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux into > perf/core > git bisect good 61f63e383784bd0ab6529cfc95ddc59c713afcc9 > # good: [3069c5a046ec92dc552194686c95e27c8c9e919d] Merge branch 'x86/asm' > git bisect good 3069c5a046ec92dc552194686c95e27c8c9e919d > # bad: [5b804ec2fd3272385ba7530c3a67d7402fb6d8a0] Merge branch 'x86/mm' > git bisect bad 5b804ec2fd3272385ba7530c3a67d7402fb6d8a0 > # good: [06c830a48346643e195801460dfe16d96ba4dff5] x86/power: Add > 5-level paging support > git bisect good 06c830a48346643e195801460dfe16d96ba4dff5 > # good: [2bbbd194fdca01f694e2ca3fb447a1acf9d19f76] Merge branch 'x86/cpu' > git bisect good 2bbbd194fdca01f694e2ca3fb447a1acf9d19f76 > # good: [69218e47994da614e7af600bf06887750ab6657a] x86: Remap GDT > tables in the fixmap section > git bisect good 69218e47994da614e7af600bf06887750ab6657a > # bad: [74c8ce958dbf0b64f198becb5d8aa93afb967438] Merge branch 'linus' > into x86/mm, to pick up a bugfix > git bisect bad 74c8ce958dbf0b64f198becb5d8aa93afb967438 > # bad: [45fc8757d1d2128e342b4e7ef39adedf7752faac] x86: Make the GDT > remapping read-only on 64-bit > git bisect bad 45fc8757d1d2128e342b4e7ef39adedf7752faac > # first bad commit: [45fc8757d1d2128e342b4e7ef39adedf7752faac] x86: > Make the GDT remapping read-only on 64-bit Just wondering, does the following commit fix it: 5b781c7e317f x86/tls: Forcibly set the accessed bit in TLS segments ? Also attached below. Thanks, Ingo =================> >From 5b781c7e317fcf9f74475dc82bfce2e359dfca13 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Sat, 18 Mar 2017 22:17:24 -0700 Subject: [PATCH] x86/tls: Forcibly set the accessed bit in TLS segments For mysterious historical reasons, struct user_desc doesn't indicate whether segments are accessed. set_thread_area() has always programmed segments as non-accessed, so the first write will set the accessed bit. This will fault if the GDT is read-only. Fix it by making TLS segments start out accessed. If this ends up breaking something, we could, in principle, leave TLS segments non-accessed and fix them up when we get the page fault. I'd be surprised, though -- AFAIK all the nasty legacy segmented programs (DOSEMU, Wine, things that run on DOSEMU and Wine, etc.) do their nasty segmented things using the LDT and not the GDT. I assume this is mainly because old OSes (Linux and otherwise) didn't historically provide APIs to do nasty things in the GDT. Fixes: 45fc8757d1d2 ("x86: Make the GDT remapping read-only on 64-bit") Signed-off-by: Andy Lutomirski Cc: Linus Torvalds Cc: Borislav Petkov Cc: Thomas Garnier Link: http://lkml.kernel.org/r/62b7748542df0164af7e0a5231283b9b13858c45.1489900519.git.luto@kernel.org Signed-off-by: Thomas Gleixner --- arch/x86/kernel/tls.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/tls.c b/arch/x86/kernel/tls.c index 6c8934406dc9..dcd699baea1b 100644 --- a/arch/x86/kernel/tls.c +++ b/arch/x86/kernel/tls.c @@ -92,10 +92,17 @@ static void set_tls_desc(struct task_struct *p, int idx, cpu = get_cpu(); while (n-- > 0) { - if (LDT_empty(info) || LDT_zero(info)) + if (LDT_empty(info) || LDT_zero(info)) { desc->a = desc->b = 0; - else + } else { fill_ldt(desc, info); + + /* + * Always set the accessed bit so that the CPU + * doesn't try to write to the (read-only) GDT. + */ + desc->type |= 1; + } ++info; ++desc; }