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 3362E34D4EA for ; Wed, 20 May 2026 08:33:25 +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=1779266007; cv=none; b=plmWPmJOzV3ZPtvWL+PPTFQxXY/twrqbEe3Fal2sj6LlRD308IDaI6fBYV20lpmGFC5EFLvOid7f8STWkL/xuxsvwrRpj3U97X2GPP1UkBjkHNRrTelrGEcwutU16DnUWc7gxr482Z84pQ2NNF/vxynmfyYCGKxTMIZ8nFHb7WA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779266007; c=relaxed/simple; bh=vGEPRPX6ZX8Y66ynLlt6pqISPcc9o7/7NkKmvEgRWyo=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=AFlY3m0b63z/YaT1V2KuuwASPVtkDTEy1+darElUww+gAsG1CgvcivOQwRsBp8KGeKgC/j18t/oCLNevKU1FvqPfx0mWhU/Opa31p1OrkayAJv4KV74+yC1PgNmWr7vG8+CjS44TUiU63fxoewBYlbSiPcxiAKZKPWvx5+p2RCw= 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=LKcU7SO/; 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="LKcU7SO/" 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 E24B0266C; Wed, 20 May 2026 01:33:18 -0700 (PDT) Received: from [10.164.19.28] (unknown [10.164.19.28]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6C7D83F85F; Wed, 20 May 2026 01:33:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1779266004; bh=vGEPRPX6ZX8Y66ynLlt6pqISPcc9o7/7NkKmvEgRWyo=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=LKcU7SO/0AajG3cfXHPYD10MOQho8VLzIRr6D8DbNr7NDZ92cxoMoPi/hzxcUkdO6 +wWWBmwtTvVA6+tJSxw+rCk5lMFW8z4Mp9KGX+RsGKHxLy5KJ7deSEdt3zj8UKPa8Z Zm3LCXdQH0kxlysuJWU9MJ4WL7rAPiZDqYiVOMsU= Message-ID: <32fd8890-7c06-4a2d-9b8d-691a2d6b44aa@arm.com> Date: Wed, 20 May 2026 14:03:14 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/3] kasan: avoid re-poisoning tag-based kmalloc redzones From: Dev Jain To: Ryan Roberts , akpm@linux-foundation.org, vbabka@kernel.org, harry@kernel.org, ryabinin.a.a@gmail.com Cc: surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, hao.li@linux.dev, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, glider@google.com, andreyknvl@gmail.com, dvyukov@google.com, vincenzo.frascino@arm.com, kasan-dev@googlegroups.com, anshuman.khandual@arm.com, catalin.marinas@arm.com References: <20260513105734.3380544-1-dev.jain@arm.com> <20260513105734.3380544-3-dev.jain@arm.com> <14da7ffe-1332-45d0-86d6-e9d9ae0a4fe0@arm.com> <2609d691-5e70-4baa-8e58-99f5ea708c6a@arm.com> <4061d696-1567-41fe-9ff9-af408ca6d4bd@arm.com> Content-Language: en-US In-Reply-To: <4061d696-1567-41fe-9ff9-af408ca6d4bd@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit > > I got the problem now. The problem is that krealloc() does not know what was the > old allocation size. > > So only talking about HW tags, can't we simply do the following. We can use > HW tags integrated init to initialize only the part we want to unpoison. > > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > index b7d05c2a6d93d..c424be3cd02bb 100644 > --- a/mm/kasan/common.c > +++ b/mm/kasan/common.c > @@ -474,7 +474,7 @@ void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flag > * Part of it might already have been unpoisoned, but it's unknown > * how big that part is. > */ > - kasan_unpoison(object, size, false); > + kasan_unpoison(object, size, want_init_on_alloc(flags)); > > slab = virt_to_slab(object); > > diff --git a/mm/slub.c b/mm/slub.c > index 0baa906f39ab8..62ee59fc389d8 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -6686,7 +6686,7 @@ __do_krealloc(const void *p, size_t new_size, unsigned long align, gfp_t flags, > goto alloc_new; > > /* Zero out spare memory. */ > - if (want_init_on_alloc(flags)) { > + if (want_init_on_alloc(flags) && !kasan_has_integrated_init()) { > kasan_disable_current(); > if (orig_size && orig_size < new_size) > memset(kasan_reset_tag(p) + orig_size, 0, new_size - orig_size); Okay, this would overwrite the data which we still need. > > > >> >