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Date: Sat, 2 Aug 2025 05:53:37 +0200
From: Ismael Luceno <ismael@iodev.co.uk>
To: YinFengwei <fengwei_yin@linux.alibaba.com>, Kees Cook <kees@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	zhourundong.zrd@linux.alibaba.com
Subject: Re: [PATCH] binfmt_elf: remove the 4k limitation of program header
 size
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In-Reply-To: <xd6zp5ytq6iakxkqoqqtseomgu5oohau4ynj3xbo7ejohpv7dv@skp2v7awzab4>

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.

Best regards.