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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D27CEF9EDCD for ; Wed, 22 Apr 2026 13:31:24 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DD9426B0088; Wed, 22 Apr 2026 09:31:23 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DB1276B008A; Wed, 22 Apr 2026 09:31:23 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CC6C26B008C; Wed, 22 Apr 2026 09:31:23 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id BC3536B0088 for ; Wed, 22 Apr 2026 09:31:23 -0400 (EDT) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 507E6138F33 for ; Wed, 22 Apr 2026 13:31:23 +0000 (UTC) X-FDA: 84686278446.26.AD8C5B4 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf05.hostedemail.com (Postfix) with ESMTP id DB69C10001B for ; Wed, 22 Apr 2026 13:31:20 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=arm.com header.s=foss header.b=ZI7EFTOO; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf05.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1776864681; a=rsa-sha256; cv=none; b=i/pZdsLKHHT1wOjWwtw/0AViLc/wevsvFaeXuvyVqMj9RSVGJdZ/RMDY4cHmLls1mlsmZk 0iFjI64PxvfgAncf3FqvByZNcFkfFdutaDHyhKF9461AuIWH0ECJ9PWP9j9Zxb+WE5DBS/ kde3zaWV6Y2Bvz6uq4Y35LWmFkW2XtE= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=arm.com header.s=foss header.b=ZI7EFTOO; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf05.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1776864681; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=h3ilUZDYyvFu9c5NsOzH/I7iI+EvkGmm6eTdjDZhFJw=; b=p8wKWkwmUYDkz7xdxeT9u512uU+8TCxxxnvIfBXT6J4DcWahtJlqKtJkSdem0ZUTaYBlty hG+eDDSb5BTn1XQbrsHkxTsxhMDLXLwvxjhO9a5gJnHvKpP7roqz+8dSF93cdfLlVU2tfk gQh490/0SbO3NuZ/iv5q8lRN7bICp4Y= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3FCA11E2F; Wed, 22 Apr 2026 06:31:14 -0700 (PDT) Received: from [10.57.89.34] (unknown [10.57.89.34]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D68F73FBD2; Wed, 22 Apr 2026 06:31:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1776864679; bh=Top9vudgGbwsB9gdK8pkIXSaPiG3wHdOl/KtxsTBaBk=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ZI7EFTOOAO8ZKkCeexRr92Fur05p/Z9cynlOaN/iWBeDk8x0fJPzRCDExPChxCMoZ jEycCoKb1uE9rzLTIdc0gQxIUZlTrxOv0LX3BRkzLxWwKLd18J4Q6N1vrnGuFQnmU5 Fp+w6T9cD3Ci3CgJZm2gKcUgGBqrSGovqraV9HFE= Message-ID: Date: Wed, 22 Apr 2026 14:31:14 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] kasan: skip HW tagging for all kernel thread stacks Content-Language: en-GB To: Catalin Marinas , "David Hildenbrand (Arm)" Cc: Muhammad Usama Anjum , Arnd Bergmann , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Kees Cook , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Uladzislau Rezki , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrey Konovalov , Marco Elver , Vincenzo Frascino , Peter Collingbourne , Will Deacon , david.hildenbrand@arm.com References: <20260324132631.482520-1-usama.anjum@arm.com> <20260324132631.482520-3-usama.anjum@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: DB69C10001B X-Rspamd-Server: rspam12 X-Stat-Signature: gjggd5z91nptt38aijxzqpr1b5ed3m5x X-Rspam-User: X-HE-Tag: 1776864680-65230 X-HE-Meta: U2FsdGVkX1/jkwzMoohHi4KVeg18dHAqpVWTAWY85v6tVAjA2nL591WUsQe88krUICqMqrvfpzHmvhF9GMiVbn/UCCTe6m8bGabwOR02ypAMGWAEiDXALLfAfHuL3wrezDA+X+zI9qPkG8zr1p8Z6hO17XAJ5PzwBn1xbaUrV0bLIXYvkV9JHvy4WO45fY34rmnF1z7qibjgfDi4KwAsrPTqqOvN2bLKj8EP/zKagQT2/yPmKU8DCCajEqrMvLRWUrgTEnGKbLMSmZrVT8YTOXyUBtv+SAsq9HymuhFo3pMG3VNPiOYrMp84vMtUNqmv8m2Mz7kfzrw0JducObtd9kXiSn3cLlLY6YUGCqkxJcBjV3IIX8gg6wI3+5XB8g3F+TPu3RtLruzTWwZ/W82GcYNzAZPkNdszsXejPI6qg/vP16OWMdh4iK2BCI45EFG60IsiAuXkBnLujRa1Uvegqgvz1Mj4kX1cLkihtrYBik3IPkdstcB4GPV80hdmQAMo6vHgmfjvIvwHEFloEsjkpE+K7eGQzI+ZbHHeb47eQDJW0s0uVYg8WkGFmH3eHfYFbFUEwEUeJvW/ekXnhYwew6KQrrlU2e1Plhnbmns/xSZuhSvGJNVwEXEowqwnUTvLxz7nATO3ihecmygu/AVYieZRCt2iFZ9zXxzpfrGJn7EsZToh9vNxfXr8+MzQziL3eKyOgpWScARs1Jaw9ZwHAfvapisgbruseGFiQ0YhNBUAX/PNiywuCVjT4Sze5zm8ViAElgvGgzpuFZF0xj8SdfJT8kkE1SYf+eZvfsXkX5pCEcJDNyVw/suRNe9ZDcvNlC0pyiB5YnjfrDo7MRsmdpdzOzxqoRoVIzjsSF4vULXLZDVMTYqVSO71FA4LvhdY4jNOQQqcmWtJZ8OedeJXlX4fHb+KQfi9XUriFN1phJw+gkrNGD2biGFcjEzopYispZIT5WV4BWCr9w4k34b G2tQlUTw DRD1lEvojn0H+NxKkMk9pys5qEaM/gYbyRVokltPTpyO/vtAV3IPkL2qSF9gCaehoA5VUI1RymsvDxq5lF4VGH98NBEvRuKnq3qKJAdLciaoVJFzP+L1hqDadrDto9g5f71kOp61+f6LhKr0QzAp3eiU7to2ZgbHIZJEkCmTJ7f67dJmHHjYfdx0DOw4j8s7qpO/cUgAyEwN0S7o9XFK4ztqn7hPRlp4RpfpTE/0cQfblYuU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 17/04/2026 09:31, Catalin Marinas wrote: > On Thu, Apr 16, 2026 at 11:03:46AM +0200, David Hildenbrand wrote: >> On 4/10/26 20:36, Catalin Marinas wrote: >>> On Fri, Apr 10, 2026 at 07:32:23PM +0100, Catalin Marinas wrote: >>>> What the original approach might help with is use-after-realloc in case >>>> we had a tagged pointer in a past life of a page and it still works now. >>>> Oh well, that's I guess for other types of hardening to address like >>>> delayed reallocation. >>> >>> Another thought (for a separate series) - we could try to map the stack >>> as Untagged (unless stack tagging is enabled; needs compiler >>> instrumentation) and enable canonical tag checking (newer addition to >>> MTE). This way, any stray tagged pointer won't work on the stack since >>> it needs a 0xf tag (canonical). >> >> Do you mean mapping it as Untagged in the vmap for CONFIG_VMAP_STACK or >> also as Untagged in the directmap? >> >> The latter brings in the set of problems with direct map fragmentation. > > Just the vmap, there are a lot more problems with the direct map. Not > sure how much it does in terms of security, maybe marginally. A > match-all tag (0xf) would still be able to access the canonically tagged > memory. > I think with the first patch in this series, we are alredy vmapping the stack memory as untagged, right? vmalloc only calls arch_vmap_pgprot_tagged() if we are not skipping kasan. So I think we already have this protection? (perhaps we need to explicitly enable the canonical tag checks?) Thanks, Ryan