From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752072AbaLRLQ3 (ORCPT ); Thu, 18 Dec 2014 06:16:29 -0500 Received: from terminus.zytor.com ([198.137.202.10]:60868 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751440AbaLRLQ1 (ORCPT ); Thu, 18 Dec 2014 06:16:27 -0500 Date: Thu, 18 Dec 2014 03:16:10 -0800 From: tip-bot for Andy Lutomirski Message-ID: Cc: tglx@linutronix.de, luto@amacapital.net, linux-kernel@vger.kernel.org, mingo@kernel.org, hpa@zytor.com, torvalds@linux-foundation.org Reply-To: linux-kernel@vger.kernel.org, luto@amacapital.net, torvalds@linux-foundation.org, mingo@kernel.org, hpa@zytor.com, tglx@linutronix.de In-Reply-To: References: To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/urgent] x86/tls: Don't validate lm in set_thread_area() after all Git-Commit-ID: 3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0 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: 3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0 Gitweb: http://git.kernel.org/tip/3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0 Author: Andy Lutomirski AuthorDate: Wed, 17 Dec 2014 14:48:30 -0800 Committer: Ingo Molnar CommitDate: Thu, 18 Dec 2014 12:12:26 +0100 x86/tls: Don't validate lm in set_thread_area() after all It turns out that there's a lurking ABI issue. GCC, when compiling this in a 32-bit program: struct user_desc desc = { .entry_number = idx, .base_addr = base, .limit = 0xfffff, .seg_32bit = 1, .contents = 0, /* Data, grow-up */ .read_exec_only = 0, .limit_in_pages = 1, .seg_not_present = 0, .useable = 0, }; will leave .lm uninitialized. This means that anything in the kernel that reads user_desc.lm for 32-bit tasks is unreliable. Revert the .lm check in set_thread_area(). The value never did anything in the first place. Fixes: 0e58af4e1d21 ("x86/tls: Disallow unusual TLS segments") Signed-off-by: Andy Lutomirski Acked-by: Thomas Gleixner Cc: stable@vger.kernel.org # Only if 0e58af4e1d21 is backported Cc: Linus Torvalds Link: http://lkml.kernel.org/r/d7875b60e28c512f6a6fc0baf5714d58e7eaadbb.1418856405.git.luto@amacapital.net Signed-off-by: Ingo Molnar --- arch/x86/include/uapi/asm/ldt.h | 7 +++++++ arch/x86/kernel/tls.c | 6 ------ 2 files changed, 7 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/uapi/asm/ldt.h b/arch/x86/include/uapi/asm/ldt.h index 46727eb..6e1aaf7 100644 --- a/arch/x86/include/uapi/asm/ldt.h +++ b/arch/x86/include/uapi/asm/ldt.h @@ -28,6 +28,13 @@ struct user_desc { unsigned int seg_not_present:1; unsigned int useable:1; #ifdef __x86_64__ + /* + * Because this bit is not present in 32-bit user code, user + * programs can pass uninitialized values here. Therefore, in + * any context in which a user_desc comes from a 32-bit program, + * the kernel must act as though lm == 0, regardless of the + * actual value. + */ unsigned int lm:1; #endif }; diff --git a/arch/x86/kernel/tls.c b/arch/x86/kernel/tls.c index 3e551ee..4e942f3 100644 --- a/arch/x86/kernel/tls.c +++ b/arch/x86/kernel/tls.c @@ -55,12 +55,6 @@ static bool tls_desc_okay(const struct user_desc *info) if (info->seg_not_present) return false; -#ifdef CONFIG_X86_64 - /* The L bit makes no sense for data. */ - if (info->lm) - return false; -#endif - return true; }