linux-kernel - Re: [RFC PATCH 0/2] Introduce a way to expose the interpreted file with binfmt

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Date:   Mon, 13 Nov 2023 14:33:13 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     Kees Cook <keescook@...omium.org>,
        David Hildenbrand <david@...hat.com>, sonicadvance1@...il.com
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, kernel-dev@...lia.com, kernel@...ccoli.net,
        ebiederm@...ssion.com, oleg@...hat.com, yzaikin@...gle.com,
        mcgrof@...nel.org, akpm@...ux-foundation.org, brauner@...nel.org,
        viro@...iv.linux.org.uk, willy@...radead.org, dave@...olabs.net,
        joshua@...ggi.es
Subject: Re: [RFC PATCH 0/2] Introduce a way to expose the interpreted file
 with binfmt_misc

On 09/10/2023 14:37, Kees Cook wrote:
> On Fri, Oct 06, 2023 at 02:07:16PM +0200, David Hildenbrand wrote:
>> On 07.09.23 22:24, Guilherme G. Piccoli wrote:
>>> Currently the kernel provides a symlink to the executable binary, in the
>>> form of procfs file exe_file (/proc/self/exe_file for example). But what
>>> happens in interpreted scenarios (like binfmt_misc) is that such link
>>> always points to the *interpreter*. For cases of Linux binary emulators,
>>> like FEX [0] for example, it's then necessary to somehow mask that and
>>> emulate the true binary path.
>>
>> I'm absolutely no expert on that, but I'm wondering if, instead of modifying
>> exe_file and adding an interpreter file, you'd want to leave exe_file alone
>> and instead provide an easier way to obtain the interpreted file.
>>
>> Can you maybe describe why modifying exe_file is desired (about which
>> consumers are we worrying? ) and what exactly FEX does to handle that (how
>> does it mask that?).
>>
>> So a bit more background on the challenges without this change would be
>> appreciated.
> 
> Yeah, it sounds like you're dealing with a process that examines
> /proc/self/exe_file for itself only to find the binfmt_misc interpreter
> when it was run via binfmt_misc?
> 
> What actually breaks? Or rather, why does the process to examine
> exe_file? I'm just trying to see if there are other solutions here that
> would avoid creating an ambiguous interface...
> 

Thanks Kees and David! Did Ryan's thorough comment addressed your
questions? Do you have any take on the TODOs?

I can maybe rebase against 6.7-rc1 and resubmit , if that makes sense!
But would be better having the TODOs addressed, I guess.

Thanks in advance for reviews and feedback on this.
Cheers,


Guilherme