From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030256AbWGaRGA (ORCPT ); Mon, 31 Jul 2006 13:06:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030257AbWGaRGA (ORCPT ); Mon, 31 Jul 2006 13:06:00 -0400 Received: from liaag2ab.mx.compuserve.com ([149.174.40.153]:59612 "EHLO liaag2ab.mx.compuserve.com") by vger.kernel.org with ESMTP id S1030256AbWGaRF7 (ORCPT ); Mon, 31 Jul 2006 13:05:59 -0400 Date: Mon, 31 Jul 2006 12:59:16 -0400 From: Chuck Ebbert <76306.1226@compuserve.com> Subject: Re: [patch] x86_64: fix is_at_popf() for compat tasks To: Andi Kleen Cc: linux-kernel , Albert Cahalan Message-ID: <200607311302_MC3-1-C69F-F0D8@compuserve.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org In-Reply-To: <200607311054.38585.ak@suse.de> On Mon, 31 Jul 2006 10:54:38 +0200, Andi Kleen wrote: > > > When testing for the REX instruction prefix, first check > > for a 32-bit task because in compat mode the REX prefix is an > > increment instruction. > > is_compat_task doesn't actually say that a task is in compat mode > (it refers to the Linux compat layer, not x86-64 compat mode) > > A better test would be regs->cs == __USER32_CS, but in theory > there could be other code segments in LDT. I guess that can > be ignored though. How about checking for regs->cs != __USER_CS instead? In 64-bit mode a program shouldn't have any other value there while in 32-bit mode it could be using LDT segments. From: Chuck Ebbert <76306.1226@compuserve.com> When testing for the REX instruction prefix, first check for 32-bit mode because in compat mode the REX prefix is an increment instruction. Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com> --- 2.6.18-rc2-64.orig/arch/x86_64/kernel/ptrace.c +++ 2.6.18-rc2-64/arch/x86_64/kernel/ptrace.c @@ -141,8 +141,11 @@ static int is_at_popf(struct task_struct case 0xf0: case 0xf2: case 0xf3: continue; - /* REX prefixes */ case 0x40 ... 0x4f: + if (regs->cs != __USER_CS) + /* 32-bit mode: register increment */ + return 0; + /* 64-bit mode: REX prefix */ continue; /* CHECKME: f0, f2, f3 */ -- Chuck