From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 64EBB2033A for ; Mon, 19 May 2025 14:19:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747664361; cv=none; b=hA1T4T1dmLMGNjdcs/qWNQa46O6B21UFgQ+nlIOO9ZYtFofYsbZGY8L2s+PbydqkKwWCCzUrUz38/YBNPMfpcdhTG5CDVjgumSTs1C7Cp24rPwbiT3nM2HuouxwXD8VKf7Ur/tZpVeBwEZWF2vHEXugtGiwQYU00qQdZIWcFq0w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747664361; c=relaxed/simple; bh=4f4X9/Vsw+237CS4qodR/LC0nJdPGsG9IRuwvyO0YHU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=VhE5SFznuw6cQVkJx1MRoYRu4S+sm/jRUAEYgJCTs2I5gGoj5RyFJ1bf/jIX36T2L4mOBOSztMAtO6u0Jrxf7LRjU80dAa5M0A7AzlTG/eJf7JjDI/oxDSImuE124l52aS89O+FzW1FWLiAW6VR5MYqnfcU/X5Yh+O4ZGnr59ig= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=vOXd5C/Z; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="vOXd5C/Z" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CB73CC4CEE4; Mon, 19 May 2025 14:19:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1747664360; bh=4f4X9/Vsw+237CS4qodR/LC0nJdPGsG9IRuwvyO0YHU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=vOXd5C/ZPLUsTdPinvyzdhuSf28mjnbqJsQ4W6zTSsldeE5YergXVU4GG3iZvysWK UuBY2Ehe6pU7JAIRf+8g/keY1vbwV9B1f8ryAax2qKAbUsw4IBFQHPEkxYPxYHtGdR 6Jm6BecKTEHpfbTaEkNjTjvYJdYa8veGc8MZq3zhOvIZmmR2SK4GNJSDC7EdM6Fw1n 44hFkr0GpVLry+DZQKGbjPbX+xGrALU3/yhykzdQt8MwTPnJtir/ZmnBvXTpsAlwP+ EuGw1gBvZOIFBGtVImWCnCDCx+NnS83SjGtE9NZk9wHufk6Rq7GZC1Gj7HURNbC5MP 3I9HhPQvqJn9w== Date: Mon, 19 May 2025 07:19:17 -0700 From: Kees Cook To: Baoquan He Cc: Coiby Xu , Andrew Morton , fuqiang wang , Vivek Goyal , Dave Young , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH v4] x86/kexec: fix potential cmem->ranges out of bounds Message-ID: <202505190716.B21F11984@keescook> References: <4de3c2onosr7negqnfhekm4cpbklzmsimgdfv33c52dktqpza5@z5pb34ghz4at> <20250507225959.174dd1eed6b0b1354c95a0fd@linux-foundation.org> <2754f4evjfumjqome63bc3inqb7ozepemejn2lcl57ryio2t6k@35l3tnn73gei> <20250509183518.bf7cd732ac667a9c20f1fee1@linux-foundation.org> <202505161616.F4C1BCCF6A@keescook> 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 Mon, May 19, 2025 at 09:22:30AM +0800, Baoquan He wrote: > On 05/16/25 at 04:20pm, Kees Cook wrote: > > On Fri, May 16, 2025 at 11:35:12AM +0800, Baoquan He wrote: > > > On 05/11/25 at 10:19am, Coiby Xu wrote: > > > > On Fri, May 09, 2025 at 06:35:18PM -0700, Andrew Morton wrote: > > > > > On Fri, 9 May 2025 17:58:01 +0800 Baoquan He wrote: > > > > > > > > > > > > The bad commit was introduced in 2021 but only recent gcc-15 supports > > > > > > > __counted_by. That's why we don't see this UBSAN warning until this > > > > > > > year. And although this UBSAN warning is scary enough, fortunately it > > > > > > > doesn't cause a real problem. > > > > > > > > > > > > > > > > > > > > > > > Baoquan, please re-review this? > > > > > > > > > > > > > > > > A -stable backport is clearly required. A Fixes: would be nice, but I > > > > > > > > assume this goes back a long time so it isn't worth spending a lot of > > > > > > > > time working out when this was introduced. > > > > > > > > > > > > > > So I believe the correct fix should be as follows, > > > > > > > > > > > > Thanks for testing and investigation into these. Could you arrange this > > > > > > into formal patches based on your testing and analysis? > > > > > > > > > > > > It would be great if you can include Fuqiang's patch since it has > > > > > > conflict with your LUKS patch. This can facilitate patch merging for > > > > > > Andrew. Thanks in advance. > > > > > > > > > > Yes please, I'm a bit lost here. > > > > > x86-kexec-fix-potential-cmem-ranges-out-of-bounds.patch is not > > > > > presently in mm.git and I'd appreciate clarity on how to resolve the > > > > > conflicts which a new version of > > > > > x86-kexec-fix-potential-cmem-ranges-out-of-bounds.patch will produce. > > > > > > > > I'll resolve any conflict between these patches. Before that, I'm not sure > > > > if a separate patch to fix the UBSAN warnings alone is needed to Cc > > > > stable@vger.kernel.org because 1) the UBSAN warnings don't mean there is a > > > > real problem; > > > > 2) both Fuqiang's patch and my kdump LUKS support patches fix the UBSAN > > > > warnings as a by-product. > > > > > > > > It seems the answer largely depends on if the stable tree or longterm > > > > trees need it. Currently, only longterm tree 6.12.28 and the stable tree > > > > 6.14.6 have the UBSAN warnings if they are compiled with gcc-15 or > > > > clang-18. Any advice will be appreciated! Thanks! > > > > > > I personally think UBSAN warning fix is not necessary for stable kernel. > > > > > > Hi Kees, Andrew, > > > > > > Could you help answer Coiby's question about whether we need post a > > > standalone patch to fix the UBSAN warning fix so that it can be back > > > ported to stable kernel? > > > > I went back through the thread and the referenced threads and I can't > > find any details on the USBAN splat. Can that please get reproduced in a > > commit log? That would help understand if it's a false positive or not. > > > The original patch is trying to fix a potential issue in which a memory > range is split, while the sub-range split out is always on top of the > entire memory range, hence no risk. > > Later, we encountered a UBSAN warning around the above memory range > splitting code several times. We found this patch can mute the warning. > > Please see below UBSAN splat trace report from Coiby: > https://lore.kernel.org/all/4de3c2onosr7negqnfhekm4cpbklzmsimgdfv33c52dktqpza5@z5pb34ghz4at/T/#u Ah-ha! Thanks for the link. > Later, Coiby got the root cause from investigation, please see: > https://lore.kernel.org/all/2754f4evjfumjqome63bc3inqb7ozepemejn2lcl57ryio2t6k@35l3tnn73gei/T/#u Looking at https://lore.kernel.org/all/aBxfflkkQXTetmbq@MiWiFi-R3L-srv/ it seems like this actually turned out to be a legitimate overflow detection? I.e. the fix isn't silencing a false positive, but rather allocating enough space? -- Kees Cook