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[23.128.96.19]) by mx.google.com with ESMTPS id j69si15174347pgd.352.2022.02.09.01.09.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Feb 2022 01:09:45 -0800 (PST) Received-SPF: softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) client-ip=23.128.96.19; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=casper.20170209 header.b=WKUHYTCu; spf=softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 79ED0DF28A70; Wed, 9 Feb 2022 00:52:19 -0800 (PST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237914AbiBFNHQ (ORCPT + 99 others); Sun, 6 Feb 2022 08:07:16 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34798 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237860AbiBFNHN (ORCPT ); Sun, 6 Feb 2022 08:07:13 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8CB8FC043182; Sun, 6 Feb 2022 05:07:12 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=O8zLbKs0X6TzxCrkjzqNkkHxAtjp2s1Oq6J6b6ynu0s=; b=WKUHYTCuz+4dtYW+6BDGdx6lbC 0OaQRA0ahdl6KWql9CtBckg55JkExEGI6yC3AH+pABNOGdgo2xCRAkXTUuw6D5KJOSqO3DYWCwul1 xyAotHf2CFbX/epQDuVxq/xDN/YIeGMNrXzAjlWDAZdeKM0nn7Pz5YVu28TI99yt4enCBvej6V4XV exkbj3EiBnKPAohE+dXpik1wBFbPp/PobtG8O3Hu45F6ZT6RMPeWL/3MrfgbWaSIk+usJ0OclAN2R zD4HC7KAj/Q7dlVumDLpRoVkqF81juNEszXWFeoryjlDzKBXTV7TgHWjiYpinUiaNfh4Cy9Gj4gD4 lkGuu/TA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nGhFH-00E7rV-11; Sun, 06 Feb 2022 13:06:24 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 245F8300470; Sun, 6 Feb 2022 14:06:19 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D86F32CA50E07; Sun, 6 Feb 2022 14:06:19 +0100 (CET) Date: Sun, 6 Feb 2022 14:06:19 +0100 From: Peter Zijlstra To: "Edgecombe, Rick P" Cc: "bsingharora@gmail.com" , "hpa@zytor.com" , "Syromiatnikov, Eugene" , "rdunlap@infradead.org" , "keescook@chromium.org" , "dave.hansen@linux.intel.com" , "kirill.shutemov@linux.intel.com" , "Eranian, Stephane" , "linux-mm@kvack.org" , "fweimer@redhat.com" , "nadav.amit@gmail.com" , "jannh@google.com" , "linux-arch@vger.kernel.org" , "kcc@google.com" , "bp@alien8.de" , "oleg@redhat.com" , "hjl.tools@gmail.com" , "Yang, Weijiang" , "Lutomirski, Andy" , "pavel@ucw.cz" , "arnd@arndb.de" , "Moreira, Joao" , "tglx@linutronix.de" , "mike.kravetz@oracle.com" , "x86@kernel.org" , "linux-doc@vger.kernel.org" , "Dave.Martin@arm.com" , "john.allen@amd.com" , "mingo@redhat.com" , "Shankar, Ravi V" , "corbet@lwn.net" , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" , "gorcunov@gmail.com" Subject: Re: [PATCH 00/35] Shadow stacks for userspace Message-ID: References: <87fsozek0j.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RDNS_NONE,SPF_HELO_NONE,T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 04, 2022 at 01:08:25AM +0000, Edgecombe, Rick P wrote: > > So how is that going to work? altstack is not an esoteric corner > > case. > > My understanding is that the main usages for the signal stack were > handling stack overflows and corruption. Since the shadow stack only > contains return addresses rather than large stack allocations, and is > not generally writable or pivotable, I thought there was a good > possibility an alt shadow stack would not end up being especially > useful. Does it seem like reasonable guesswork? altstacks are also used in userspace threading implemenations.