linux-kernel - Re: [PATCH] binfmt_elf: dynamically allocate note.data in parse_elf

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Message-ID: <202306071417.79F70AC@keescook>
Date:   Wed, 7 Jun 2023 14:19:51 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christian Marangi <ansuelsmth@...il.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Mark Brown <broonie@...nel.org>,
        Dave Martin <Dave.Martin@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] binfmt_elf: dynamically allocate note.data in
 parse_elf_properties

On Wed, Jun 07, 2023 at 04:42:27PM +0200, Christian Marangi wrote:
> Dynamically allocate note.data in parse_elf_properties to fix
> compilation warning on some arch.

I'd rather avoid dynamic allocation as much as possible in the exec
path, but we can balance it against how much it may happen.

> On some arch note.data exceed the stack limit for a single function and
> this cause the following compilation warning:
> fs/binfmt_elf.c: In function 'parse_elf_properties.isra':
> fs/binfmt_elf.c:821:1: error: the frame size of 1040 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
>   821 | }
>       | ^
> cc1: all warnings being treated as errors

Which architectures see this warning?

> Fix this by dynamically allocating the array.
> Update the sizeof of the union to the biggest element allocated.

How common are these notes? I assume they're very common; I see them
even in /bin/true:

$ readelf -lW /bin/true | grep PROP
  GNU_PROPERTY   0x000338 0x0000000000000338 0x0000000000000338 0x000030 0x000030 R   0x8

-- 
Kees Cook