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Date:   Mon, 07 Aug 2023 07:45:08 -0700
From:   Kees Cook <kees@kernel.org>
To:     =?ISO-8859-1?Q?Pali_Roh=E1r?= <pali@kernel.org>,
        Eric Biederman <ebiederm@xmission.com>,
        Kees Cook <keescook@chromium.org>
CC:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: binfmt_misc & different PE binaries
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On August 6, 2023 9:23:46 AM PDT, "Pali Roh=C3=A1r" <pali@kernel=2Eorg> wro=
te:
>Hello, I would like to remind this email about binfmt_misc for PE=2E
>
>On Thursday 06 July 2023 13:55:50 Pali Roh=C3=A1r wrote:
>> Hello,
>>=20
>> I would like to ask how to properly register binfmt_misc for different
>> PE binaries, so kernel could execute the correct loader for them=2E
>>=20
>> I mean, how to register support for Win32 (console/gui) PE binaries and
>> also for CLR PE binaries (dotnet)=2E Win32 needs to be executed under w=
ine
>> and CLR ideally under dotnet core (or mono)=2E
>>=20
>> I have read kernel documentation files admin-guide/binfmt-misc=2Erst
>> and admin-guide/mono=2Erst=2E But seems that they are in conflicts as b=
oth
>> wants to registers its own handler for the same magic:
>>=20
>>   echo ':DOSWin:M::MZ::/usr/local/bin/wine:' > register
>>=20
>>   echo ':CLR:M::MZ::/usr/bin/mono:' > /proc/sys/fs/binfmt_misc/register
>>=20
>> Not mentioning the fact that they register DOS MZ handler, which matche=
s
>> not only all PE binaries (including EFI, libraries, other processors),
>> but also all kind of other NE/LE/LX binaries and different DOS extender=
s=2E
>>=20
>> 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=2E And distinguish between Win32 and CLR
>> needs to parse PE COM descriptor directory=2E
>>=20
>> 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 whate=
ver it needs to do to further distinguish the binary and hand it off to the=
 appropriate loader=2E


--=20
Kees Cook