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Date:   Mon, 7 Aug 2023 19:08:52 +0200
From:   Pali =?utf-8?B?Um9ow6Fy?= <pali@kernel.org>
To:     Kees Cook <kees@kernel.org>
Cc:     Eric Biederman <ebiederm@xmission.com>,
        Kees Cook <keescook@chromium.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: binfmt_misc & different PE binaries
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On Monday 07 August 2023 07:45:08 Kees Cook wrote:
> On August 6, 2023 9:23:46 AM PDT, "Pali Rohár" <pali@kernel.org> wrote:
> >Hello, I would like to remind this email about binfmt_misc for PE.
> >
> >On Thursday 06 July 2023 13:55:50 Pali Rohár wrote:
> >> Hello,
> >> 
> >> I would like to ask how to properly register binfmt_misc for different
> >> PE binaries, so kernel could execute the correct loader for them.
> >> 
> >> I mean, how to register support for Win32 (console/gui) PE binaries and
> >> also for CLR PE binaries (dotnet). Win32 needs to be executed under wine
> >> and CLR ideally under dotnet core (or mono).
> >> 
> >> I have read kernel documentation files admin-guide/binfmt-misc.rst
> >> and admin-guide/mono.rst. But seems that they are in conflicts as both
> >> wants to registers its own handler for the same magic:
> >> 
> >>   echo ':DOSWin:M::MZ::/usr/local/bin/wine:' > register
> >> 
> >>   echo ':CLR:M::MZ::/usr/bin/mono:' > /proc/sys/fs/binfmt_misc/register
> >> 
> >> Not mentioning the fact that they register DOS MZ handler, which matches
> >> not only all PE binaries (including EFI, libraries, other processors),
> >> but also all kind of other NE/LE/LX binaries and different DOS extenders.
> >> 
> >> From documentation it looks like that even registering PE binaries is
> >> impossible by binfmt_misc as PE is detected by checking that indirect
> >> reference from 0x3C is PE\0\0. And distinguish between Win32 and CLR
> >> needs to parse PE COM descriptor directory.
> >> 
> >> Or it is possible to write binfmt_misc pattern match based on indirect
> >> offset?
> 
> Normally a single userspace program will be registered and it can do whatever it needs to do to further distinguish the binary and hand it off to the appropriate loader.
> 
> 
> 
> -- 
> Kees Cook

Ok, so you are saying that there should be one userspace program which
distinguish between DOS, CLR and Win32 and then exec the correct
"runtime" loader? Is there such one? Also it would be nice to mention it
in the documentation.