From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-99.freemail.mail.aliyun.com (out30-99.freemail.mail.aliyun.com [115.124.30.99]) (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 89B5B2E371F for ; Mon, 4 Aug 2025 02:18:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.99 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754273912; cv=none; b=iAG8uF0k+t58zq87CPtM6sgKDn0p79vs0TPQsVxf7MzEWkM4ZkFnYx2Dw7lnrMA/mRw6/mpaqYcFF/67rLeIZJ/D9R4PSIeUSpsRiy21UZcwK2rE6DYhsTKqcdBVtm3Tm3igAdYObGJLP0oMCLY/v16Pt7Txwpqgm1VIvAgfWEE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754273912; c=relaxed/simple; bh=3u/E2kX8x2JoMQ307KLHEWOBM8a9yv1whcRiWU7O/Do=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ClfcgDRlJBgxWAImBw03fUWJTJvBvUMJt05Tp2sPzQRO0eAP9wUk/UK0fZD7OkVUX9BjgLbtGKrDYf/WxbKQUZybBfkZyujqrIaNuLMMiHa0dTtTYrlMF6c3K61BDdtaUmqUsILiCb8veh7zshLHAXDUbgzP8VA5AmTIQEt79F4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=pnbnTLvB; arc=none smtp.client-ip=115.124.30.99 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="pnbnTLvB" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1754273901; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=fOhE5iGHrZ4xjSv36/UXuUcfl5os1bpqTbIaxe2NUiE=; b=pnbnTLvBFSCHT7mKIYNk6SHWst2Xtgk8XHAK/JgvyML0qRFUi3X32u7NeNpljRtzzqbgzkJn6X7SqMuJ6QLvLpMWMP6tS6Kx3DD2T1TlxJD1FfyKdJ3bePAg4/0TDZFnWo8RodWsy+MO6PBu5r4EAgJrCr4xJ57R9SQ/IiqmkOY= Received: from 30.21.176.60(mailfrom:fengwei_yin@linux.alibaba.com fp:SMTPD_---0WktbLhr_1754273572 cluster:ay36) by smtp.aliyun-inc.com; Mon, 04 Aug 2025 10:13:03 +0800 Message-ID: <6653242a-5b08-48ff-a126-9e9367633420@linux.alibaba.com> Date: Mon, 4 Aug 2025 10:12:52 +0800 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] binfmt_elf: remove the 4k limitation of program header size To: Ismael Luceno , Kees Cook Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, zhourundong.zrd@linux.alibaba.com, fengwei_yin@linux.alibaba.com References: <202508021029.7CC8B334@keescook> From: Yin Fengwei In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2025/8/3 13:28, Ismael Luceno 写道: > On 02/Aug/2025 10:29, Kees Cook wrote: >> On Sat, Aug 02, 2025 at 05:47:13AM +0200, Ismael Luceno wrote: >>> On Sat, Jul 19, 2025 at 17:17:09 +0800, YinFengwei wrote: >>>> On Thu, Jul 17, 2025 at 04:31:50PM +0800, Kees Cook wrote: >>>>> On Thu, 17 Jul 2025 19:01:08 +0800, fengwei_yin@linux.alibaba.com wrote: >>>>>> We have assembly code generated by a script. GCC successfully compiles >>>>>> it. However, the kernel cannot load it on an ARM64 platform with a 4K >>>>>> page size. In contrast, the same ELF file loads correctly on the same >>>>>> platform with a 64K page size. >>>>>> >>>>>> The root cause is the Linux kernel's ELF_MIN_ALIGN limitation on the >>>>>> program headers of ELF files. The ELF file contains 78 program headers >>>>>> (the script inserts many holes when generating the assembly code). On >>>>>> ARM64 with a 4K page size, the ELF_MIN_ALLIGN enforces a maximum of 74 >>>>>> program headers, causing the ELF file to fail. However, with a 64K page >>>>>> size, the ELF_MIN_ALIGN is relaxed to over 1,184 program headers, allowing >>>>>> the file to run correctly. >>>>>> >>>>>> [...] >>>>> >>>>> Applied to for-next/execve, thanks! >>>> Cook, thanks a lot. >>>> >>>> Regards >>>> Yin, Fengwei >>>> >>>>> >>>>> [1/1] binfmt_elf: remove the 4k limitation of program header size >>>>> https://git.kernel.org/kees/c/8030790477e8 >>>>> >>>>> Take care, >>> >>> Hi, >>> >>> I noticed this removal and wonder whether it could be a problem on >>> smaller platforms. >>> >>> IIRC that code has been there since ELF support was added in one >>> form or another; and the idea behind it was to simplify the code >>> by ensuring no cross-page reads could happen, as these could cause >>> undefined behaviours or read abort exceptions. >> >> I didn't see a place where that would happen -- the reads aren't done on >> a single page. If you see something that I missed, please let me know! > > The offset to the phdrs can point anywhere and the entries are > arbitrarily sized, thus it can be unaligned, so we can be potentially > reading at an entry right between two pages. The read buffer are managed in kernel. Why cross-page read can cause undefined behaviors or read abort? Does smaller platforms have special behavior in this situation? Like can't do cross-page read against the buffer allocated by kmalloc? Regards Yin, Fengwei