From: Pavel Machek <pavel@ucw.cz>
To: madvenka@linux.microsoft.com
Cc: kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org,
linux-kernel@vger.kernel.org,
linux-security-module@vger.kernel.org, oleg@redhat.com,
x86@kernel.org, luto@kernel.org, David.Laight@ACULAB.COM,
fweimer@redhat.com, mark.rutland@arm.com, mic@digikod.net
Subject: Re: [PATCH v2 0/4] [RFC] Implement Trampoline File Descriptor
Date: Wed, 23 Sep 2020 10:14:26 +0200 [thread overview]
Message-ID: <20200923081426.GA30279@amd> (raw)
In-Reply-To: <20200922215326.4603-1-madvenka@linux.microsoft.com>
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Hi!
> Introduction
> ============
>
> Dynamic code is used in many different user applications. Dynamic code is
> often generated at runtime. Dynamic code can also just be a pre-defined
> sequence of machine instructions in a data buffer. Examples of dynamic
> code are trampolines, JIT code, DBT code, etc.
>
> Dynamic code is placed either in a data page or in a stack page. In order
> to execute dynamic code, the page it resides in needs to be mapped with
> execute permissions. Writable pages with execute permissions provide an
> attack surface for hackers. Attackers can use this to inject malicious
> code, modify existing code or do other harm.
>
> To mitigate this, LSMs such as SELinux implement W^X. That is, they may not
> allow pages to have both write and execute permissions. This prevents
> dynamic code from executing and blocks applications that use it. To allow
> genuine applications to run, exceptions have to be made for them (by setting
> execmem, etc) which opens the door to security issues.
>
> The W^X implementation today is not complete. There exist many user level
> tricks that can be used to load and execute dynamic code. E.g.,
>
> - Load the code into a file and map the file with R-X.
>
> - Load the code in an RW- page. Change the permissions to R--. Then,
> change the permissions to R-X.
>
> - Load the code in an RW- page. Remap the page with R-X to get a separate
> mapping to the same underlying physical page.
>
> IMO, these are all security holes as an attacker can exploit them to inject
> his own code.
IMO, you are smoking crack^H^H very seriously misunderstanding what
W^X is supposed to protect from.
W^X is not supposed to protect you from attackers that can already do
system calls. So loading code into a file then mapping the file as R-X
is in no way security hole in W^X.
If you want to provide protection from attackers that _can_ do system
calls, fine, but please don't talk about W^X and please specify what
types of attacks you want to prevent and why that's good thing.
Hint: attacker that can "Load the code into a file and map the file
with R-X." can probably also load the code into /foo and
os.system("/usr/bin/python /foo").
This is not first crazy patch from your company. Perhaps you should
have a person with strong Unix/Linux experience performing "straight
face test" on outgoing patches?
Best regards,
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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next prev parent reply other threads:[~2020-09-23 8:14 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <210d7cd762d5307c2aa1676705b392bd445f1baa>
2020-09-16 15:08 ` [PATCH v2 0/4] [RFC] Implement Trampoline File Descriptor madvenka
2020-09-16 15:08 ` [PATCH v2 1/4] [RFC] fs/trampfd: Implement the trampoline file descriptor API madvenka
2020-09-16 15:08 ` [PATCH v2 2/4] [RFC] x86/trampfd: Provide support for the trampoline file descriptor madvenka
2020-09-16 15:08 ` [PATCH v2 3/4] [RFC] arm64/trampfd: " madvenka
2020-09-16 15:08 ` [PATCH v2 4/4] [RFC] arm/trampfd: " madvenka
2020-09-17 1:04 ` [PATCH v2 0/4] [RFC] Implement Trampoline File Descriptor Florian Weimer
2020-09-17 15:36 ` Madhavan T. Venkataraman
2020-09-17 15:57 ` Madhavan T. Venkataraman
2020-09-17 16:01 ` Florian Weimer
2020-09-23 1:46 ` Arvind Sankar
2020-09-23 9:11 ` Arvind Sankar
2020-09-23 19:17 ` Madhavan T. Venkataraman
2020-09-23 19:51 ` Arvind Sankar
2020-09-23 23:51 ` Madhavan T. Venkataraman
2020-09-24 20:23 ` Madhavan T. Venkataraman
2020-09-24 20:52 ` Florian Weimer
2020-09-25 22:22 ` Madhavan T. Venkataraman
2020-09-27 18:25 ` Madhavan T. Venkataraman
2020-09-24 22:13 ` Pavel Machek
2020-09-24 23:43 ` Arvind Sankar
2020-09-25 22:44 ` Madhavan T. Venkataraman
2020-09-26 15:55 ` Arvind Sankar
2020-09-27 17:59 ` Madhavan T. Venkataraman
2020-09-22 21:53 ` madvenka
2020-09-22 21:53 ` [PATCH v2 1/4] [RFC] fs/trampfd: Implement the trampoline file descriptor API madvenka
2020-09-22 21:53 ` [PATCH v2 2/4] [RFC] x86/trampfd: Provide support for the trampoline file descriptor madvenka
2020-09-22 21:53 ` [PATCH v2 3/4] [RFC] arm64/trampfd: " madvenka
2020-09-22 21:53 ` [PATCH v2 4/4] [RFC] arm/trampfd: " madvenka
2020-09-22 21:54 ` [PATCH v2 0/4] [RFC] Implement Trampoline File Descriptor Madhavan T. Venkataraman
2020-09-23 8:14 ` Pavel Machek [this message]
2020-09-23 9:14 ` Solar Designer
2020-09-23 14:11 ` Solar Designer
2020-09-23 15:18 ` Pavel Machek
2020-09-23 18:00 ` Solar Designer
2020-09-23 18:21 ` Solar Designer
2020-09-23 14:39 ` Florian Weimer
2020-09-23 18:09 ` Andy Lutomirski
2020-09-23 18:11 ` Solar Designer
2020-09-23 18:49 ` Arvind Sankar
2020-09-23 23:53 ` Madhavan T. Venkataraman
2020-09-23 19:41 ` Madhavan T. Venkataraman
2020-09-23 18:10 ` James Morris
2020-09-23 18:32 ` Madhavan T. Venkataraman
2020-09-23 8:42 ` Pavel Machek
2020-09-23 18:56 ` Madhavan T. Venkataraman
2020-09-23 20:51 ` Pavel Machek
2020-09-23 23:04 ` Madhavan T. Venkataraman
2020-09-24 16:44 ` Mickaël Salaün
2020-09-24 22:05 ` Pavel Machek
2020-09-25 10:12 ` Mickaël Salaün
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