From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753142AbcKUIHf (ORCPT ); Mon, 21 Nov 2016 03:07:35 -0500 Received: from terminus.zytor.com ([198.137.202.10]:55448 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753038AbcKUIHd (ORCPT ); Mon, 21 Nov 2016 03:07:33 -0500 Date: Mon, 21 Nov 2016 00:04:58 -0800 From: tip-bot for Andy Lutomirski Message-ID: Cc: peterz@infradead.org, bp@alien8.de, brgerst@gmail.com, torvalds@linux-foundation.org, dvlasenk@redhat.com, jpoimboe@redhat.com, tedheadster@gmail.com, luto@kernel.org, linux-kernel@vger.kernel.org, mingo@kernel.org, tglx@linutronix.de, hpa@zytor.com Reply-To: jpoimboe@redhat.com, dvlasenk@redhat.com, torvalds@linux-foundation.org, luto@kernel.org, linux-kernel@vger.kernel.org, tedheadster@gmail.com, peterz@infradead.org, bp@alien8.de, brgerst@gmail.com, tglx@linutronix.de, hpa@zytor.com, mingo@kernel.org In-Reply-To: References: To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/urgent] x86/traps: Ignore high word of regs->cs in early_fixup_exception() Git-Commit-ID: fc0e81b2bea0ebceb71889b61d2240856141c9ee X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: fc0e81b2bea0ebceb71889b61d2240856141c9ee Gitweb: http://git.kernel.org/tip/fc0e81b2bea0ebceb71889b61d2240856141c9ee Author: Andy Lutomirski AuthorDate: Sat, 19 Nov 2016 18:42:40 -0800 Committer: Ingo Molnar CommitDate: Mon, 21 Nov 2016 08:06:54 +0100 x86/traps: Ignore high word of regs->cs in early_fixup_exception() On the 80486 DX, it seems that some exceptions may leave garbage in the high bits of CS. This causes sporadic failures in which early_fixup_exception() refuses to fix up an exception. As far as I can tell, this has been buggy for a long time, but the problem seems to have been exacerbated by commits: 1e02ce4cccdc ("x86: Store a per-cpu shadow copy of CR4") e1bfc11c5a6f ("x86/init: Fix cr4_init_shadow() on CR4-less machines") This appears to have broken for as long as we've had early exception handling. [ Note to stable maintainers: This patch is needed all the way back to 3.4, but it will only apply to 4.6 and up, as it depends on commit: 0e861fbb5bda ("x86/head: Move early exception panic code into early_fixup_exception()") If you want to backport to kernels before 4.6, please don't backport the prerequisites (there was a big chain of them that rewrote a lot of the early exception machinery); instead, ask me and I can send you a one-liner that will apply. ] Reported-by: Matthew Whitehead Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: stable@vger.kernel.org Fixes: 4c5023a3fa2e ("x86-32: Handle exception table entries during early boot") Link: http://lkml.kernel.org/r/cb32c69920e58a1a58e7b5cad975038a69c0ce7d.1479609510.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/mm/extable.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c index 79ae939..fcd06f7 100644 --- a/arch/x86/mm/extable.c +++ b/arch/x86/mm/extable.c @@ -135,7 +135,12 @@ void __init early_fixup_exception(struct pt_regs *regs, int trapnr) if (early_recursion_flag > 2) goto halt_loop; - if (regs->cs != __KERNEL_CS) + /* + * Old CPUs leave the high bits of CS on the stack + * undefined. I'm not sure which CPUs do this, but at least + * the 486 DX works this way. + */ + if ((regs->cs & 0xFFFF) != __KERNEL_CS) goto fail; /*