Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932948AbeALAzJ (ORCPT + 1 other); Thu, 11 Jan 2018 19:55:09 -0500 Received: from mga02.intel.com ([134.134.136.20]:13998 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932148AbeALAzG (ORCPT ); Thu, 11 Jan 2018 19:55:06 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,346,1511856000"; d="scan'208";a="19445414" Subject: [PATCH v2 05/19] x86: implement ifence_array_ptr() and array_ptr_mask() From: Dan Williams To: linux-kernel@vger.kernel.org Cc: linux-arch@vger.kernel.org, kernel-hardening@lists.openwall.com, x86@kernel.org, Ingo Molnar , "H. Peter Anvin" , tglx@linutronix.de, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@linux.intel.com Date: Thu, 11 Jan 2018 16:46:51 -0800 Message-ID: <151571801167.27429.316440257610732033.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <151571798296.27429.7166552848688034184.stgit@dwillia2-desk3.amr.corp.intel.com> References: <151571798296.27429.7166552848688034184.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: StGit/0.17.1-9-g687f MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: 'ifence_array_ptr' is provided as an alternative to the default '__array_ptr' implementation that uses a mask to sanitize user controllable pointers. Later patches will allow it to be selected via kernel command line. The '__array_ptr' implementation otherwise appears safe for current generation cpus across multiple architectures. 'array_ptr_mask' is used by the default 'array_ptr' implementation to cheaply calculate an array bounds mask. Suggested-by: Linus Torvalds Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: x86@kernel.org Signed-off-by: Dan Williams --- arch/x86/include/asm/barrier.h | 42 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h index b04f572d6d97..4450d25d8cde 100644 --- a/arch/x86/include/asm/barrier.h +++ b/arch/x86/include/asm/barrier.h @@ -28,6 +28,48 @@ #define ifence() alternative_2("", "mfence", X86_FEATURE_MFENCE_RDTSC, \ "lfence", X86_FEATURE_LFENCE_RDTSC) +/** + * ifence_array_ptr - Generate a pointer to an array element, + * ensuring the pointer is bounded under speculation. + * + * @arr: the base of the array + * @idx: the index of the element + * @sz: the number of elements in the array + * + * If @idx falls in the interval [0, @sz), returns the pointer to + * @arr[@idx], otherwise returns NULL. + */ +#define ifence_array_ptr(arr, idx, sz) \ +({ \ + typeof(*(arr)) *__arr = (arr), *__ret; \ + typeof(idx) __idx = (idx); \ + typeof(sz) __sz = (sz); \ + \ + __ret = __idx < __sz ? __arr + __idx : NULL; \ + ifence(); \ + __ret; \ +}) + +/** + * array_ptr_mask - generate a mask for array_ptr() that is ~0UL when + * the bounds check succeeds and 0 otherwise + */ +#define array_ptr_mask array_ptr_mask +static inline unsigned long array_ptr_mask(unsigned long idx, unsigned long sz) +{ + unsigned long mask; + + /* + * mask = index - size, if that result is >= 0 then the index is + * invalid and the mask is 0 else ~0 + */ + asm ("cmpq %1,%2; sbbq %0,%0;" + :"=r" (mask) + :"r"(sz),"r" (idx) + :"cc"); + return mask; +} + #ifdef CONFIG_X86_PPRO_FENCE #define dma_rmb() rmb() #else