Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754883AbaDXIz6 (ORCPT ); Thu, 24 Apr 2014 04:55:58 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:46970 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754811AbaDXIzq (ORCPT ); Thu, 24 Apr 2014 04:55:46 -0400 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Linus Torvalds , "H. Peter Anvin" , Luis Henriques Subject: [PATCH 3.11 144/182] x86-64, modify_ldt: Ban 16-bit segments on 64-bit kernels Date: Thu, 24 Apr 2014 09:51:09 +0100 Message-Id: <1398329507-5911-145-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1398329507-5911-1-git-send-email-luis.henriques@canonical.com> References: <1398329507-5911-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.11.10.9 -stable review patch. If anyone has any objections, please let me know. ------------------ From: "H. Peter Anvin" commit b3b42ac2cbae1f3cecbb6229964a4d48af31d382 upstream. The IRET instruction, when returning to a 16-bit segment, only restores the bottom 16 bits of the user space stack pointer. We have a software workaround for that ("espfix") for the 32-bit kernel, but it relies on a nonzero stack segment base which is not available in 32-bit mode. Since 16-bit support is somewhat crippled anyway on a 64-bit kernel (no V86 mode), and most (if not quite all) 64-bit processors support virtualization for the users who really need it, simply reject attempts at creating a 16-bit segment when running on top of a 64-bit kernel. Cc: Linus Torvalds Signed-off-by: H. Peter Anvin Link: http://lkml.kernel.org/n/tip-kicdm89kzw9lldryb1br9od0@git.kernel.org Signed-off-by: Luis Henriques --- arch/x86/kernel/ldt.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c index ebc9873..af1d14a 100644 --- a/arch/x86/kernel/ldt.c +++ b/arch/x86/kernel/ldt.c @@ -229,6 +229,17 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode) } } + /* + * On x86-64 we do not support 16-bit segments due to + * IRET leaking the high bits of the kernel stack address. + */ +#ifdef CONFIG_X86_64 + if (!ldt_info.seg_32bit) { + error = -EINVAL; + goto out_unlock; + } +#endif + fill_ldt(&ldt, &ldt_info); if (oldmode) ldt.avl = 0; -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/