From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 904FA331218; Fri, 17 Apr 2026 08:31:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776414681; cv=none; b=AoNFns/plaCijm+1AY9jAX1BampaHIOumvz32sQUT2SzGFiY4/vinqxeR4ZTMNlq9ul27O6LF7GvPmHNPa5hfGV8K7FIzzB+xWimQp3ILmM/wEePMsrBXi586lgVfbFccJqbZrMReNOPPCgxDdDOcgGTL293kxylAOP+AE58nF8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776414681; c=relaxed/simple; bh=Xf8oSVlSyjbs13J2X0kdO8ZpK0071NFBikk2L1e0ZT0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=YTy0VXiqU0Ih8AGccxO0G6Ac32ISAZO+bDbkTVuzC/HespO48MzFTzXFICYc2Lum97RhXOi8sOmwcy/IK/YebEcDOooHLbyw5VYKPePJld1L/UQsuxKfcgBFXzzVs02+YyFAFKXbJ+y7HlM19mSJYzqKS/eyM5h3eyZ217XVtdg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=tZgojb2e; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="tZgojb2e" 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 E2FF51E7D; Fri, 17 Apr 2026 01:31:12 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 235843F641; Fri, 17 Apr 2026 01:31:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1776414678; bh=Xf8oSVlSyjbs13J2X0kdO8ZpK0071NFBikk2L1e0ZT0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=tZgojb2evQ6/7+DClcXpyLa99zzRDpUS7S0mVhSbZhXIt0RPhE/BPySCWlI6E2NHK KPE8JCU3bOeXhjZ/k47vt0jDLgArIHpRRZNbU2Ju8E0bWimOItBpxk5rNzeDT8az5m g7QTTyHdiLu7/ZHOEJT2o8LaOxRwWwqLBwRqKEgY= Date: Fri, 17 Apr 2026 09:31:10 +0100 From: Catalin Marinas To: "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 , Ryan.Roberts@arm.com, david.hildenbrand@arm.com Subject: Re: [PATCH v2 2/3] kasan: skip HW tagging for all kernel thread stacks Message-ID: References: <20260324132631.482520-1-usama.anjum@arm.com> <20260324132631.482520-3-usama.anjum@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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. -- Catalin