From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758562AbbAGC6z (ORCPT ); Tue, 6 Jan 2015 21:58:55 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:46230 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756929AbbAGBwC (ORCPT ); Tue, 6 Jan 2015 20:52:02 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Andy Lutomirski , Thomas Gleixner , Linus Torvalds , Ingo Molnar Subject: [PATCH 3.18 40/84] x86/tls: Dont validate lm in set_thread_area() after all Date: Tue, 6 Jan 2015 17:49:43 -0800 Message-Id: <20150107014030.322760318@linuxfoundation.org> X-Mailer: git-send-email 2.2.1 In-Reply-To: <20150107014029.012974975@linuxfoundation.org> References: <20150107014029.012974975@linuxfoundation.org> User-Agent: quilt/0.63-1 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 3.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Andy Lutomirski commit 3fb2f4237bb452eb4e98f6a5dbd5a445b4fed9d0 upstream. 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: Linus Torvalds Link: http://lkml.kernel.org/r/d7875b60e28c512f6a6fc0baf5714d58e7eaadbb.1418856405.git.luto@amacapital.net Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/uapi/asm/ldt.h | 7 +++++++ arch/x86/kernel/tls.c | 6 ------ 2 files changed, 7 insertions(+), 6 deletions(-) --- 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 }; --- a/arch/x86/kernel/tls.c +++ b/arch/x86/kernel/tls.c @@ -55,12 +55,6 @@ static bool tls_desc_okay(const struct u 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; }