From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752165AbbJGLKI (ORCPT ); Wed, 7 Oct 2015 07:10:08 -0400 Received: from mail.skyhub.de ([78.46.96.112]:43764 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751329AbbJGLKG (ORCPT ); Wed, 7 Oct 2015 07:10:06 -0400 Date: Wed, 7 Oct 2015 13:10:38 +0200 From: Borislav Petkov To: Andy Lutomirski Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Brian Gerst , Denys Vlasenko , Linus Torvalds Subject: Re: [PATCH v2 05/36] x86/entry/64/compat: Fix SYSENTER's NT flag before user memory access Message-ID: <20151007111038.GC5046@nazgul.tnic> References: <19eb235828b2d2a52c53459e09f2974e15e65a35.1444091584.git.luto@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <19eb235828b2d2a52c53459e09f2974e15e65a35.1444091584.git.luto@kernel.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 05, 2015 at 05:47:53PM -0700, Andy Lutomirski wrote: > Clearing NT is part of the prologue, whereas loading up arg6 makes > more sense to think about as part of syscall processing. Reorder > them. > > Signed-off-by: Andy Lutomirski > --- > arch/x86/entry/entry_64_compat.S | 18 +++++++++--------- > 1 file changed, 9 insertions(+), 9 deletions(-) > > diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S > index a9360d40fb7f..aa76864a8a6b 100644 > --- a/arch/x86/entry/entry_64_compat.S > +++ b/arch/x86/entry/entry_64_compat.S > @@ -89,15 +89,6 @@ ENTRY(entry_SYSENTER_compat) > sub $(10*8), %rsp /* pt_regs->r8-11, bp, bx, r12-15 not saved */ > > /* > - * no need to do an access_ok check here because rbp has been > - * 32-bit zero extended > - */ > - ASM_STAC > -1: movl (%rbp), %ebp > - _ASM_EXTABLE(1b, ia32_badarg) > - ASM_CLAC > - > - /* > * Sysenter doesn't filter flags, so we need to clear NT > * ourselves. To save a few cycles, we can check whether > * NT was set instead of doing an unconditional popfq. > @@ -106,6 +97,15 @@ ENTRY(entry_SYSENTER_compat) > jnz sysenter_fix_flags > sysenter_flags_fixed: Btw, do I see it correctly that we can save us this jumping to sysenter_fix_flags and back to sysenter_flags_fixed? Label is jumped to only once and the couple of insns there can be behind a JZ... -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. --