From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Mon, 06 Jun 2016 00:26:54 +0200 (CEST) Received: from mail.linuxfoundation.org ([140.211.169.12]:32946 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S27042507AbcFEWY5tjkIj (ORCPT ); Mon, 6 Jun 2016 00:24:57 +0200 Received: from localhost (c-50-170-35-168.hsd1.wa.comcast.net [50.170.35.168]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id F3BCF2C; Sun, 5 Jun 2016 22:24:47 +0000 (UTC) From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Paul Burton , Michal Toman , Aaro Koskinen , James Hogan , linux-mips@linux-mips.org, Ralf Baechle Subject: [PATCH 4.5 017/128] MIPS: Prevent "restoration" of MSA context in non-MSA kernels Date: Sun, 5 Jun 2016 15:22:52 -0700 Message-Id: <20160605222321.758151709@linuxfoundation.org> X-Mailer: git-send-email 2.8.3 In-Reply-To: <20160605222321.183131188@linuxfoundation.org> References: <20160605222321.183131188@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 53867 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: gregkh@linuxfoundation.org Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips 4.5-stable review patch. If anyone has any objections, please let me know. ------------------ From: Paul Burton commit 6533af4d4831c421cd9aa4dce7cfc19a3514cc09 upstream. If a kernel doesn't support MSA context (ie. CONFIG_CPU_HAS_MSA=n) then it will only keep 64 bits per FP register in thread context, and the calls to set_fpr64 in restore_msa_extcontext will overrun the end of the FP register context into the FCSR & MSACSR values. GCC 6.x has become smart enough to detect this & complain like so: arch/mips/kernel/signal.c: In function 'protected_restore_fp_context': ./arch/mips/include/asm/processor.h:114:17: error: array subscript is above array bounds [-Werror=array-bounds] fpr->val##width[FPR_IDX(width, idx)] = val; \ ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~ ./arch/mips/include/asm/processor.h:118:1: note: in expansion of macro 'BUILD_FPR_ACCESS' BUILD_FPR_ACCESS(64) The only way to trigger this code to run would be for a program to set up an artificial extended MSA context structure following a sigframe & execute sigreturn. Whilst this doesn't allow a program to write to any state that it couldn't already, it makes little sense to allow this "restoration" of MSA context in a system that doesn't support MSA. Fix this by killing a program with SIGSYS if it tries something as crazy as "restoring" fake MSA context in this way, also fixing the build error & allowing for most of restore_msa_extcontext to be optimised out of kernels without support for MSA. Signed-off-by: Paul Burton Reported-by: Michal Toman Fixes: bf82cb30c7e5 ("MIPS: Save MSA extended context around signals") Tested-by: Aaro Koskinen Cc: James Hogan Cc: Michal Toman Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/13164/ Signed-off-by: Ralf Baechle Signed-off-by: Greg Kroah-Hartman --- arch/mips/kernel/signal.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- a/arch/mips/kernel/signal.c +++ b/arch/mips/kernel/signal.c @@ -195,6 +195,9 @@ static int restore_msa_extcontext(void _ unsigned int csr; int i, err; + if (!config_enabled(CONFIG_CPU_HAS_MSA)) + return SIGSYS; + if (size != sizeof(*msa)) return -EINVAL; @@ -398,8 +401,8 @@ int protected_restore_fp_context(void __ } fp_done: - if (used & USED_EXTCONTEXT) - err |= restore_extcontext(sc_to_extcontext(sc)); + if (!err && (used & USED_EXTCONTEXT)) + err = restore_extcontext(sc_to_extcontext(sc)); return err ?: sig; }