From: Jaskaran Singh Khurana <jaskarankhurana@linux.microsoft.com>
To: "Mickaël Salaün" <mic@digikod.net>
Cc: Deven Bowers <deven.desai@linux.microsoft.com>,
agk@redhat.com, axboe@kernel.dk, snitzer@redhat.com,
jmorris@namei.org, serge@hallyn.com, zohar@linux.ibm.com,
linux-integrity@vger.kernel.org,
linux-security-module@vger.kernel.org, dm-devel@redhat.com,
linux-block@vger.kernel.org, jannh@google.com,
tyhicks@linux.microsoft.com, pasha.tatashin@soleen.com,
sashal@kernel.org, nramas@linux.microsoft.com,
mdsakib@linux.microsoft.com, linux-kernel@vger.kernel.org,
corbet@lwn.net
Subject: Re: [RFC PATCH v3 00/12] Integrity Policy Enforcement LSM (IPE)
Date: Tue, 26 May 2020 13:44:45 -0700 (PDT) [thread overview]
Message-ID: <alpine.LRH.2.21.2005261343540.83057@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.inter> (raw)
In-Reply-To: <alpine.LRH.2.21.2005161420490.8455@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.inter>
[-- Attachment #1: Type: text/plain, Size: 4975 bytes --]
Hello Mickael,
Could you please share your thoughts for the below proposal.
Regards,
JK
On Sat, 16 May 2020, Jaskaran Singh Khurana wrote:
>
> Hello Mickael,
>
> On Thu, 14 May 2020, Mickaël Salaün wrote:
>
>>
>> On 12/05/2020 22:46, Deven Bowers wrote:
>>>
>>>
>>> On 5/11/2020 11:03 AM, Deven Bowers wrote:
>>>>
>>>>
>>>> On 5/10/2020 2:28 AM, Mickaël Salaün wrote:
>>>>
>>>> [...snip]
>>>>
>>>>>>
>>>>>> Additionally, rules are evaluated top-to-bottom. As a result, any
>>>>>> revocation rules, or denies should be placed early in the file to
>>>>>> ensure
>>>>>> that these rules are evaluated before a rule with "action=ALLOW" is
>>>>>> hit.
>>>>>>
>>>>>> IPE policy is designed to be forward compatible and backwards
>>>>>> compatible,
>>>>>> thus any failure to parse a rule will result in the line being
>>>>>> ignored,
>>>>>> and a warning being emitted. If backwards compatibility is not
>>>>>> required,
>>>>>> the kernel commandline parameter and sysctl, ipe.strict_parse can be
>>>>>> enabled, which will cause these warnings to be fatal.
>>>>>
>>>>> Ignoring unknown command may lead to inconsistent beaviors. To achieve
>>>>> forward compatibility, I think it would be better to never ignore
>>>>> unknown rule but to give a way to userspace to known what is the
>>>>> current
>>>>> kernel ABI. This could be done with a securityfs file listing the
>>>>> current policy grammar.
>>>>>
>>>>
>>>> That's a fair point. From a manual perspective, I think this is fine.
>>>> A human-user can interpret a grammar successfully on their own when new
>>>> syntax is introduced.
>>>>
>>>> From a producing API perspective, I'd have to think about it a bit
>>>> more. Ideally, the grammar would be structured in such a way that the
>>>> userland
>>>> interpreter of this grammar would not have to be updated once new syntax
>>>> is introduced, avoiding the need to update the userland binary. To do so
>>>> generically ("op=%s") is easy, but doesn't necessarily convey sufficient
>>>> information (what happens when a new "op" token is introduced?). I think
>>>> this may come down to regular expression representations of valid values
>>>> for these tokens, which worries me as regular expressions are incredibly
>>>> error-prone[1].
>>>>
>>>> I'll see what I can come up with regarding this.
>>>
>>> I have not found a way that I like to expose some kind of grammar
>>> through securityfs that can be understood by usermode to parse the
>>> policy. Here's what I propose as a compromise:
>>>
>>> 1. I remove the unknown command behavior. This address your
>>> first point about inconsistent behaviors, and effectively removes the
>>> strict_parse sysctl (as it is always enabled).
>>>
>>> 2. I introduce a versioning system for the properties
>>> themselves. The valid set of properties and their versions
>>> can be found in securityfs, under say, ipe/config in a key=value
>>> format where `key` indicates the understood token, and `value`
>>> indicates their current version. For example:
>>>
>>> $ cat $SECURITYFS/ipe/config
>>> op=1
>>> action=1
>>> policy_name=1
>>> policy_version=1
>>> dmverity_signature=1
>>> dmverity_roothash=1
>>> boot_verified=1
>>
>> The name ipe/config sounds like a file to configure IPE. Maybe something
>> like ipe/config_abi or ipe/config_grammar?
>>
>>>
>>> if new syntax is introduced, the version number is increased.
>>>
>>> 3. The format of those versions are documented as part of
>>> the admin-guide around IPE. If user-mode at that point wants to rip
>>> the documentation formats and correlate with the versioning, then
>>> it fulfills the same functionality as above, with out the complexity
>>> around exposing a parsing grammar and interpreting it on-the-fly.
>>> Many of these are unlikely to move past version 1, however.
>>>
>>> Thoughts?
>>>
>>
>> That seems reasonable.
>>
>
> There is a use case for not having strict parsing in the cloud world where
> there are multiple versions of OS deployed across a large number of systems
> say 100,000 nodes. An OS update can take weeks to complete across all the
> nodes, and we end up having a heterogeneous mix of OS versions.
>
> Without non-strict parsing, to fix an issue in a policy we will need to
> update the various versions of the policy (one each for all OS versions
> which have different IPE policy schema). We will lose the agility we need to
> fix and deploy something urgently in the policy, the nodes might be failing
> some critical workloads meanwhile. All the various versions of the policy
> will need to be changed and production signed then deployed etc. Further some
> versions might introduce newer issues and we will need to see what all
> versions of the policy have that bug.
>
> I propose keeping the non-strict option as well to cater to this use case.
> Let me know your thoughts on this.
>
> Regards,
> JK
>
next prev parent reply other threads:[~2020-05-26 20:44 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-15 16:25 [RFC PATCH v3 00/12] Integrity Policy Enforcement LSM (IPE) deven.desai
2020-04-15 16:25 ` [RFC PATCH v3 01/12] scripts: add ipe tooling to generate boot policy deven.desai
2020-04-15 16:25 ` [RFC PATCH v3 02/12] security: add ipe lsm evaluation loop and audit system deven.desai
2020-04-15 16:25 ` [RFC PATCH v3 03/12] security: add ipe lsm policy parser and policy loading deven.desai
2020-07-15 19:16 ` Tyler Hicks
2020-04-15 16:25 ` [RFC PATCH v3 04/12] ipe: add property for trust of boot volume deven.desai
2020-04-15 16:25 ` [RFC PATCH v3 05/12] fs: add security blob and hooks for block_device deven.desai
2020-04-22 16:42 ` James Morris
2020-04-22 16:55 ` Casey Schaufler
2020-04-15 16:25 ` [RFC PATCH v3 06/12] dm-verity: move signature check after tree validation deven.desai
2020-04-15 16:25 ` [RFC PATCH v3 07/12] dm-verity: add bdev_setsecurity hook for dm-verity signature deven.desai
2020-04-15 16:25 ` [RFC PATCH v3 08/12] ipe: add property for signed dmverity volumes deven.desai
2020-04-15 16:25 ` [RFC PATCH v3 09/12] dm-verity: add bdev_setsecurity hook for root-hash deven.desai
2020-04-15 16:25 ` [RFC PATCH v3 10/12] ipe: add property for dmverity roothash deven.desai
2020-04-15 16:25 ` [RFC PATCH v3 11/12] documentation: add ipe documentation deven.desai
2020-04-15 16:25 ` [RFC PATCH v3 12/12] cleanup: uapi/linux/audit.h deven.desai
2020-05-10 9:28 ` [RFC PATCH v3 00/12] Integrity Policy Enforcement LSM (IPE) Mickaël Salaün
2020-05-11 18:03 ` Deven Bowers
2020-05-12 20:46 ` Deven Bowers
2020-05-14 19:28 ` Mickaël Salaün
2020-05-16 22:14 ` Jaskaran Singh Khurana
2020-05-26 20:44 ` Jaskaran Singh Khurana [this message]
2020-05-29 8:18 ` Mickaël Salaün
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