From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752945AbcLGHIU (ORCPT ); Wed, 7 Dec 2016 02:08:20 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:58070 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752894AbcLGHIS (ORCPT ); Wed, 7 Dec 2016 02:08:18 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "H. Peter Anvin" , Matthew Whitehead , Andy Lutomirski Subject: [PATCH 4.4 04/13] x86/traps: Ignore high word of regs->cs in early_fixup_exception() Date: Wed, 7 Dec 2016 08:07:43 +0100 Message-Id: <20161207070716.507248027@linuxfoundation.org> X-Mailer: git-send-email 2.10.2 In-Reply-To: <20161207070716.317145973@linuxfoundation.org> References: <20161207070716.317145973@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Andy Lutomirski commit fc0e81b2bea0ebceb71889b61d2240856141c9ee upstream. 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. [ This backport should apply to kernels from 3.4 - 4.5. ] Fixes: 4c5023a3fa2e ("x86-32: Handle exception table entries during early boot") Cc: H. Peter Anvin Reported-by: Matthew Whitehead Signed-off-by: Andy Lutomirski Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/head_32.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/x86/kernel/head_32.S +++ b/arch/x86/kernel/head_32.S @@ -571,7 +571,7 @@ early_idt_handler_common: movl %eax,%ds movl %eax,%es - cmpl $(__KERNEL_CS),32(%esp) + cmpw $(__KERNEL_CS),32(%esp) jne 10f leal 28(%esp),%eax # Pointer to %eip