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From: "Mickaël Salaün" <mic@digikod.net>
To: Pavel Machek <pavel@ucw.cz>
Cc: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>,
	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
Subject: Re: [PATCH v2 0/4] [RFC] Implement Trampoline File Descriptor
Date: Fri, 25 Sep 2020 12:12:01 +0200	[thread overview]
Message-ID: <eec5d097-c70f-365b-3548-66726ad49f04@digikod.net> (raw)
In-Reply-To: <20200924220540.GA13185@amd>


On 25/09/2020 00:05, Pavel Machek wrote:
> Hi!
> 
>>>>> I believe you should simply delete confusing "introduction" and
>>>>> provide details of super-secure system where your patches would be
>>>>> useful, instead.
>>>>
>>>> This RFC talks about converting dynamic code (which cannot be authenticated)
>>>> to static code that can be authenticated using signature verification. That
>>>> is the scope of this RFC.
>>>>
>>>> If I have not been clear before, by dynamic code, I mean machine code that is
>>>> dynamic in nature. Scripts are beyond the scope of this RFC.
>>>>
>>>> Also, malware compiled from sources is not dynamic code. That is orthogonal
>>>> to this RFC. If such malware has a valid signature that the kernel permits its
>>>> execution, we have a systemic problem.
>>>>
>>>> I am not saying that script authentication or compiled malware are not problems.
>>>> I am just saying that this RFC is not trying to solve all of the security problems.
>>>> It is trying to define one way to convert dynamic code to static code to address
>>>> one class of problems.
>>>
>>> Well, you don't have to solve all problems at once.
>>>
>>> But solutions have to exist, and AFAIK in this case they don't. You
>>> are armoring doors, but ignoring open windows.
>>
>> FYI, script execution is being addressed (for the kernel part) by this
>> patch series:
>> https://lore.kernel.org/lkml/20200924153228.387737-1-mic@digikod.net/
> 
> Ok.
> 
>>> Or very probably you are thinking about something different than
>>> normal desktop distros (Debian 10). Because on my systems, I have
>>> python, gdb and gcc...
>>
>> It doesn't make sense for a tailored security system to leave all these
>> tools available to an attacker.
> 
> And it also does not make sense to use "trampoline file descriptor" on
> generic system... while W^X should make sense there.

Well, as said before, (full/original/system-wide) W^X may require
trampfd (as well as other building-blocks).

I guess most Linux deployments are not on "generic systems"
anyway (even if they may be based on generic distros), and W^X
contradicts the fact that users/attackers can do whatever they want on
the system.

> 
>>> It would be nice to specify what other pieces need to be present for
>>> this to make sense -- because it makes no sense on Debian 10.
>>
>> Not all kernel features make sense for a generic/undefined usage,
>> especially specific security mechanisms (e.g. SELinux, Smack, Tomoyo,
>> SafeSetID, LoadPin, IMA, IPE, secure/trusted boot, lockdown, etc.), but
>> they can still be definitely useful.
> 
> Yep... so... I'd expect something like... "so you have single-purpose
> system

No one talked about a single-purpose system.

> with all script interpreters removed,

Not necessarily with the patch series I pointed out just before.

> IMA hashing all the files
> to make sure they are not modified, and W^X enabled.

System-wide W^X is not only for memory, and as Madhavan said: "this RFC
pertains to converting dynamic [writable] machine code to static
[non-writable] code".

> Attacker can
> still execute code after buffer overflow by .... and trapoline file
> descriptor addrsses that"... so that people running generic systems
> can stop reading after first sentence.

Are you proposing to add a
"[feature-not-useful-without-a-proper-system-configuration]" tag in
subjects? :)

      reply	other threads:[~2020-09-25 10:18 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <210d7cd762d5307c2aa1676705b392bd445f1baa>
2020-09-16 15:08 ` 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
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 [this message]

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