From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BD171C433DB for ; Sun, 28 Mar 2021 14:19:01 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 2841561935 for ; Sun, 28 Mar 2021 14:19:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2841561935 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 3E3026B0036; Sun, 28 Mar 2021 10:19:00 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 393746B006C; Sun, 28 Mar 2021 10:19:00 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 25AE16B006E; Sun, 28 Mar 2021 10:19:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0251.hostedemail.com [216.40.44.251]) by kanga.kvack.org (Postfix) with ESMTP id 097626B0036 for ; Sun, 28 Mar 2021 10:19:00 -0400 (EDT) Received: from smtpin37.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id BFDD3A8E8 for ; Sun, 28 Mar 2021 14:18:59 +0000 (UTC) X-FDA: 77969489598.37.08D8A3C Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by imf27.hostedemail.com (Postfix) with ESMTP id 3B30580192C0 for ; Sun, 28 Mar 2021 14:18:54 +0000 (UTC) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1616941137; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8jt5HUbqaBbpJnFpBonfd9d+7RkA3BHSrsmyPxYI6Ow=; b=MPtduieEpysU4q9js5b0yPqytBVqj1yGGjDnyAvsGIVcZRlh1fGCuPgfVVgOBFKMBTNevn fLl17KJGqS+zzYhMdcfKfoWMZEiIOJ/1IxDriACV0viIjOxWGlZer8SDDiVpAwayddS5Nr dKzFubYqsIfVfviXl0oePNENDLeHuSpGRwsjxcNazb1vgd/tTLiqC1L11q9sk3HJj7auzp 2RFKTUCCknRw1+XvPIFRYtgjlb9HqycmRITXwMVyD29pfWJb/DT40AZ2N0HulmJEyJJdyi wHhXCK0OW2CGaOTWyHH5SniDM+3e2+oAlwxo6M7w6ZpvQul1zg54QDaFYymMpw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1616941137; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8jt5HUbqaBbpJnFpBonfd9d+7RkA3BHSrsmyPxYI6Ow=; b=HnBEwLsP7QX3vSPeVDkKOWL7X+V2OXCZ1w0icw1CyJUPckQDr18pNfiQHYF3yrMy/hE0TQ adt3cwnSbiDqF5Cw== To: Kees Cook Cc: Kees Cook , Elena Reshetova , x86@kernel.org, Andy Lutomirski , Peter Zijlstra , Catalin Marinas , Will Deacon , Mark Rutland , Alexander Potapenko , Alexander Popov , Ard Biesheuvel , Jann Horn , Vlastimil Babka , David Hildenbrand , Mike Rapoport , Andrew Morton , Jonathan Corbet , Randy Dunlap , kernel-hardening@lists.openwall.com, linux-hardening@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 4/6] x86/entry: Enable random_kstack_offset support In-Reply-To: <20210319212835.3928492-5-keescook@chromium.org> References: <20210319212835.3928492-1-keescook@chromium.org> <20210319212835.3928492-5-keescook@chromium.org> Date: Sun, 28 Mar 2021 16:18:56 +0200 Message-ID: <87h7kvcqen.ffs@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 3B30580192C0 X-Stat-Signature: fs7oxrxtpdyrei47y7xfw4gxmrrdiauy Received-SPF: none (linutronix.de>: No applicable sender policy available) receiver=imf27; identity=mailfrom; envelope-from=""; helo=galois.linutronix.de; client-ip=193.142.43.55 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616941134-396673 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Mar 19 2021 at 14:28, Kees Cook wrote: > + > + /* > + * x86_64 stack alignment means 3 bits are ignored, so keep > + * the top 5 bits. x86_32 needs only 2 bits of alignment, so > + * the top 6 bits will be used. > + */ > + choose_random_kstack_offset(rdtsc() & 0xFF); Comment mumbles about 5/6 bits and the TSC value is masked with 0xFF and then the applied offset is itself limited with 0x3FF. Too many moving parts for someone who does not have the details of all this memorized. Thanks, tglx