linux-kernel - RE: [PATCH] x86: Remove a.out support

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Date:   Thu, 17 Mar 2022 02:32:29 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Kees Cook' <keescook@...omium.org>,
        James Jones <linux@...innocuous.com>,
        Arnd Bergmann <arnd@...db.de>
CC:     Borislav Petkov <bp@...en8.de>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] x86: Remove a.out support

From: Kees Cook
> Sent: 16 March 2022 22:30
> 
> On Wed, Mar 16, 2022 at 01:38:31PM +0100, Arnd Bergmann wrote:
> > is in the end, but it's likely easier than a standalone a.out loader
> > in user space, or a conversion to ELF format.
> 
> Yeah, the exec format is really simple. The only tricky bit was preparing
> the stack and making sure everything landed in the right place for text
> and data. James, can you try this? aln and mac run for me, but I'm not
> actually exercising them beyond dumping argument lists, etc:

Doesn't that restrict the a.out program to the address space below
the normal base address for elf programs?
So you'll only be able to load small programs - which might be ok here.

OTOH it might be possible to link the 'loader program' to a high
address - the elf loader will probably just load it.
Best to link it static to avoid shared lib mmaps
and probably try to avoid libc calls.

I was wondering what happens when malloc() starts using
sbrk() - but I guess it sees the top of the bss for the
loaded and it all works fine.

	David

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