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 798B31C84A0 for ; Wed, 20 May 2026 04:32:32 +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=1779251554; cv=none; b=UmkDrkn/Frnfd7g9CL+xIDWaRuyTihlyEn8vewJyOtR5XAuCeDPlcXJuKL/1adYhjiaMtY/Lmo04GPJkwrWfEVezSNzJXQyN8gikMcg1eimKcd+AlEDciiz/tfy9fRQ3KL77nPlOgX47W8gyZLzmUjgOLWpCF7+cl7NiKayt6Ro= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779251554; c=relaxed/simple; bh=uK8/vpqcmE/MoIIzLPGgkI5PWGz3hNqG9Y+RY4UbO8E=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=mVojdlV2q6nKQOE3jb3QU3kBcrko0iZZ4gbr18YgVZ7MG1UleBjFKVAtahvh620oR9R5j0DMvT4Rr3aX4hvOQ64Qagj41LP4Mb3Hdzr1HUgduzAbxL44ngtwtA4cimiHYhrs5zTwsyGBP6W7rGHUpHtzZ8hl310EkZNE4HiEsvc= 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=aFpgww/L; 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="aFpgww/L" 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 A538815A1; Tue, 19 May 2026 21:32:26 -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 50CAE3F85F; Tue, 19 May 2026 21:32:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1779251551; bh=uK8/vpqcmE/MoIIzLPGgkI5PWGz3hNqG9Y+RY4UbO8E=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=aFpgww/Lz0nJH9vrNo4YXwGE4j65EOqHYsycy2EMXUZ+5Wz9oFwlfZkKujrRWQKRv y2dNkcQzNeOkKfyO28Kcqz+wPyhypQfLGzMuLp3Pb9/gMUKKDZ5M5woPUmLlCXMpJN 97ZMwvLLVIKtZYj+wYOaVoHxCjHz0oDrUHQjMRbU= Message-ID: Date: Wed, 20 May 2026 10:02:22 +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: 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, ryan.roberts@arm.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> Content-Language: en-US In-Reply-To: <14da7ffe-1332-45d0-86d6-e9d9ae0a4fe0@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit > > Problem 1: > > p = kzalloc(96, GFP_KERNEL); // kmalloc-128 > p = krealloc(p, 120, GFP_KERNEL | __GFP_ZERO); > > Before my patch, kzalloc zeroed bytes 0..127, krealloc exposes bytes 96..119 > which are already zero from kzalloc. > > After my patch, kzalloc zeroes only 0..95, krealloc may think old > size is 128, so it does not zero 96..119, 96..119 may contain stale data. > > Why is this a problem? Surely caller of krealloc shouldn't be > relying on a previous zeroing. krealloc documentation explicitly says that > GFP_ZERO is ignored. My bad for looking at a very old tree :( the documentation in the upstream kernel does not say that.