Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754175AbeALBLY (ORCPT + 1 other); Thu, 11 Jan 2018 20:11:24 -0500 Received: from mail-it0-f65.google.com ([209.85.214.65]:46354 "EHLO mail-it0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754016AbeALBLV (ORCPT ); Thu, 11 Jan 2018 20:11:21 -0500 X-Google-Smtp-Source: ACJfBot2K+n0g9mV6AhqamIKI/c39nEzWTzcB67rx7NGTw8oEwfxq40ltXLwamU0J4Lmc9VJKXvPtis9G2HRCbVi/fE= MIME-Version: 1.0 In-Reply-To: <151571802814.27429.12886210130791656117.stgit@dwillia2-desk3.amr.corp.intel.com> References: <151571798296.27429.7166552848688034184.stgit@dwillia2-desk3.amr.corp.intel.com> <151571802814.27429.12886210130791656117.stgit@dwillia2-desk3.amr.corp.intel.com> From: Linus Torvalds Date: Thu, 11 Jan 2018 17:11:20 -0800 X-Google-Sender-Auth: 5mtAkW-AZzkJ_6Z531_bemJSkak Message-ID: Subject: Re: [PATCH v2 08/19] x86: use __uaccess_begin_nospec and ASM_IFENCE in get_user paths To: Dan Williams Cc: Linux Kernel Mailing List , linux-arch@vger.kernel.org, Andi Kleen , Kees Cook , kernel-hardening@lists.openwall.com, "the arch/x86 maintainers" , Ingo Molnar , Al Viro , "H. Peter Anvin" , Thomas Gleixner , Andrew Morton , Alan Cox Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: This patch doesn't affect arch/x86/lib/getuser.S, which I find surprising. Of all the user access functions, I actually think that get_user() is the one most likely to have the result then used speculatively as an index (the required second dependent read to actually leak data). I do *not* see people doing "copy_from_user()" and then somehow using the thing as an index to another array. I mean, it can happen (copy a structure, use a member in that structure), but it doesn't seem to be the most likely thing. The most likely thing would seem to be some random ioctl() do a "get_user()" to get an index, and then using that index. That would seem to be one of the easier ways to perhaps get that kind of kernel spectre attack. Adding the ASM_IFENCE to __get_user_X() in arch/x86/lib/getuser.S would seem to go naturally together with the copy_user_64.S changes in this patch. Is there some reason __get_user_X() was overlooked? Those are _the_ most common user accessor functions that do the address limit checking. Linus