From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f174.google.com (mail-pl1-f174.google.com [209.85.214.174]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E203529D28F for ; Wed, 25 Mar 2026 03:00:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774407604; cv=none; b=FfWfZrT24LlgILvMGO5u4jwkCDyaIoEgqza5s1mYvZ21EH1OpqD4tpq3Xt9qkSkLHLSC5NpE0oOKzW56A9fHxajpCQisafeMlHGhCPs7tpK3el57miK35yqmS3thDbpisaLRLFKRPRBWhX8Ixxei+ArrOtNR+e+ZGRNz95AGdHA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774407604; c=relaxed/simple; bh=0SO1ezB5xqF/jDhtcvBmzZdac5PSbbdtiGl6pp7jGto=; h=Date:From:To:cc:Subject:In-Reply-To:Message-ID:References: MIME-Version:Content-Type; b=XNaKYfkI+NmBupIGFBFs7g2gmxoI7xq8AtksRsAmGrduvmv6sqzwRa5/9pY9vlGEtyxR/SsYjDXN8idngDJecBGBfrwPBTYBp9BAjmCxGYmAYg6adjlno31553G3RyLdl6u0z8XsKGpvWOkMXOPu4PyG7XcvTii1Ck9yQ2M8FQA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=v6/cH9K/; arc=none smtp.client-ip=209.85.214.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="v6/cH9K/" Received: by mail-pl1-f174.google.com with SMTP id d9443c01a7336-2b04c9e3eb7so47035ad.0 for ; Tue, 24 Mar 2026 20:00:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1774407602; x=1775012402; darn=vger.kernel.org; h=mime-version:references:message-id:in-reply-to:subject:cc:to:from :date:from:to:cc:subject:date:message-id:reply-to; bh=GLCYT1BBJZAVEfo2dGruLL5s+wMzYpDGhybdNbcCskE=; b=v6/cH9K/KJV8k+4pbK2EYKQvhHvuuLNsE3PuKZC0PL8gGbLmqQNLq+x1nqXbTX5ANM OkA+RKSliwucjd7lVS5gA30n7emjb4BK5lGcPa4u2eA80OTbKaSLRzDzIfLP+pjI8Kff DRGvu8ou+/OL7C0DcX+6eftFAJRSkXVAjUqKdVo8tSyaBLHQBZc32Lv+6gjQlNViJU6s C1Fy4weN6dsDqFCFenAJM6OsYQ9upgipfdCPHtMbhh1nMDQHH8V8A4s9hk01URwW6kdW YkaGuNhCFx5F714acjSIrqtx7DfuJKAUTeQer18LD0yDzl/48BLxjrH/6Mlv1tSAiZ58 NOiA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1774407602; x=1775012402; h=mime-version:references:message-id:in-reply-to:subject:cc:to:from :date:x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=GLCYT1BBJZAVEfo2dGruLL5s+wMzYpDGhybdNbcCskE=; b=QrQlTz5c9Ef8gSWpFu4h775w4dmL6BDRyM95NyWfwaRWJgbnClqKaeuD0NDIqbJRSo 5Dg56mfdKhVsmxtEgL12euVVbLeADbhky1p3P/nMXDtD8axASP9SCy+yCWssekGJu3wv hN7OmTCqVxGF4xniRH2hBycROhdBvZjhnGPRGwqDXK04pJVOOOuJvb47hN+2Qky08rq6 pRN4XbcxCDh57AzZPHOzAN96myBeghaV2s0r7kIDByuKDi3xJaPwz++TA/rorSWC2Mcr 5SoI5ggdR1pbAUjyXaYvbjUTOVmoq7CJG0l6b21AR1dDNrI8UBI1psfQWHeTS6/ePBKx pGYw== X-Forwarded-Encrypted: i=1; AJvYcCU80DwyX+OglH+QEMwi/ZGYx+z9nKTXntSxFyJczGqQUw0CMAP7c6R9zBd7ou7rq+Mau8GPiQ02pUy56pQ=@vger.kernel.org X-Gm-Message-State: AOJu0YyjrcJ8wMoNRKQjME0L3xb5tIwJ6VTH9TvD5HJ/BQTqHF8Fia1A e8vHdM2CATY6u8VPRe5xBnZNgueGneULnpVDCb1/QIhWV4pypeeq2cFjG4RsHwaqOQ== X-Gm-Gg: ATEYQzxaxjKsspduHkPNP/NJaN0EpV/8wvYQKqhAYAlFI8EZpKVtfwqfU+qrxJ9dkZ1 bKFDA+N9HEPQ5TlsWl9Wb9FK5pNaBtTZviZrkaV3dr1DXBp2dE4SZL+HotdRqsDFjzGG9dEW/f5 tq6g3A84Mj30C58H28x/D/VwkmOlg+xoXijGKkPpiovTbFoffL58HlXcT07eOfCJGYSrZMCaHja etSa8vAr47dDGP4+7c+45jlCIiBq8ZAkLyELiordHqw5OR5WqXrx2Glu53T/UUABubTrSy490Bo iEWgcH8Wtwgi7hIwHSLNZNAnl4hj99pj2tjR4MV7AkPhOip7qCmGIeJJjPmzn4r5yhB4QtHf0dR QrSu+swlFGGuTndLJFdaB7jDcT+xtqH9w1Oqu1Zm9q6BiIS2kxImKCwmQO2AQdn4zCw9/tkZSXf WdPt7Q10FPIrT8bPRwryi9pPItBUgZrUBwJ8MLH00hE52HUsH6c3ar35hYxJ/NInohddmb+F9/8 wBAuzMTrIX0EPDV7PR4S5CxnB/0jRv9mYBH7o4B6yqRltgPcR0= X-Received: by 2002:a17:902:ea12:b0:2ae:575b:2345 with SMTP id d9443c01a7336-2b0b2a3f61bmr1084935ad.9.1774407601650; Tue, 24 Mar 2026 20:00:01 -0700 (PDT) Received: from [2a00:79e0:2eb0:8:5267:b1e5:66fd:936] ([2a00:79e0:2eb0:8:5267:b1e5:66fd:936]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82b03bc6881sm16083424b3a.22.2026.03.24.20.00.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Mar 2026 20:00:01 -0700 (PDT) Date: Tue, 24 Mar 2026 20:00:00 -0700 (PDT) From: David Rientjes To: Jann Horn cc: Vlastimil Babka , Harry Yoo , Andrew Morton , Hao Li , Christoph Lameter , Roman Gushchin , "Paul E. McKenney" , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Dmitry Vyukov , rcu@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] slab,rcu: disable KVFREE_RCU_BATCHED for strict grace period In-Reply-To: <20260324-kasan-kfree-rcu-v1-1-ac58a7a13d03@google.com> Message-ID: References: <20260324-kasan-kfree-rcu-v1-1-ac58a7a13d03@google.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 On Tue, 24 Mar 2026, Jann Horn wrote: > Disable CONFIG_KVFREE_RCU_BATCHED in CONFIG_RCU_STRICT_GRACE_PERIOD builds > so that kernel fuzzers have an easier time finding use-after-free involving > kfree_rcu(). > > The intent behind CONFIG_RCU_STRICT_GRACE_PERIOD is that RCU should invoke > callbacks and free objects as soon as possible (at a large performance > cost) so that kernel fuzzers and such have an easier time detecting > use-after-free bugs in objects with RCU lifetime. > > CONFIG_KVFREE_RCU_BATCHED is a performance optimization that queues > RCU-freed objects in ways that CONFIG_RCU_STRICT_GRACE_PERIOD can't > expedite; for example, the following testcase doesn't trigger a KASAN splat > when CONFIG_KVFREE_RCU_BATCHED is enabled: > ``` > struct foo_struct { > struct rcu_head rcu; > int a; > }; > struct foo_struct *foo = kmalloc(sizeof(*foo), > GFP_KERNEL | __GFP_NOFAIL | __GFP_ZERO); > > pr_info("%s: calling kfree_rcu()\n", __func__); > kfree_rcu(foo, rcu); > msleep(10); > pr_info("%s: start UAF access\n", __func__); > READ_ONCE(foo->a); > pr_info("%s: end UAF access\n", __func__); > ``` > > Signed-off-by: Jann Horn Acked-by: David Rientjes