Re: [RFC] Persist ima logs to disk

From: Raphael Gianotti <raphgi@linux.microsoft.com>
To: Mimi Zohar <zohar@linux.ibm.com>, janne.karhunen@gmail.com
Cc: linux-integrity@vger.kernel.org, tusharsu@linux.microsoft.com,
	tyhicks@linux.microsoft.com, nramas@linux.microsoft.com,
	balajib@linux.microsoft.com, Amir Goldstein <amir73il@gmail.com>
Subject: Re: [RFC] Persist ima logs to disk
Date: Thu, 7 Jan 2021 10:32:14 -0800	[thread overview]
Message-ID: <3425fcf5-8735-f1ba-8b4a-03b5b49a79e7@linux.microsoft.com> (raw)
In-Reply-To: <87127d502bcb9707dd4e7a43475ab6bed2fdd421.camel@linux.ibm.com>


On 1/7/2021 7:06 AM, Mimi Zohar wrote:
> [Cc: Amir Goldstein]
>
> On Tue, 2021-01-05 at 11:57 -0800, Raphael Gianotti wrote:
>> IMA measures files and buffer data and some systems may end up
>> generating lots of entries in the IMA measurement list. This list is
>> kept in kernel memoryc and as it grows in size it could end up taking
>> too many resources, causing the system to run out of available
>> memory. During kexec, the IMA measurement list can be carried over in
>> memory, but it's possible for the list to become too large for that
>> to happen.
>>
>> The Kconfig introduced in this series enables admins to configure a
>> maximum number of entries and a file to export the IMA measurement
>> list to whenever the set limit is reached.
>>
>> The list is written out in append mode, so the system will keep
>> writing new entries as long as it stays running or runs out of
>> space. Whenever the export file is set, it's truncated. If writing
>> to the export list fails, a flag is set to prevent further exports,
>> as the file is likely in a bad state. Setting a new export file
>> resets this flag, allowing exports to resume and giving admins a way
>> to recover from this state if necessary.
>>
>> In the case of kexec, if the list is too large too be carried over in
>> memory and an export file is configured, the list will be exported,
>> preventing the measurements from being lost during kexec.
>>
>> This code is based off of a previous RFC sent by Janne Karhunen[1],
>> and is intended to pick up where that was left off.
>>
>> In a thread with Janne Karhunen[2], it was mentioned that another
>> approach, using mm had been considered. Upon some investigation the
>> approach used in this RFC still seemed adequate for solving this
>> problem.
>>
>> [1] https://patchwork.kernel.org/project/linux-integrity/patch/201912
>> 20074929.8191-1-janne.karhunen@gmail.com/
>> [2] https://lore.kernel.org/linux-integrity/CAE=NcrbdS-3gVvnnEwdNSOLO
>> vTenLjyppDz2aJACGRgBYSh=Gw@mail.gmail.com/
>>
>> Signed-off-by: Raphael Gianotti <raphgi@linux.microsoft.com>
> My original concerns of truncating the IMA measurement list have not
> been addressed.  Once the IMA measurement list has been truncated,
> quoting and then verifying any of the PCRs contained in the measurement
> list will fail, unless the measurements have been preserved and are
> readily accessible.
>
> Amir's suggestion addresses kernel memory constraints without
> truncating the IMA measurement list.
>
> Mimi
I actually wasn't aware of what the exact concerns were since I couldn't 
find the
original discussion around it, I only knew that had been suggested and 
thought
it was mostly due to it being a more elegant solution. In my in looking 
into it I might
have overcomplicated, from looking at a reply from Janne. I will revisit 
that with this
in mind as it seems then this solution won't be able to address the PCR 
concerns.

Raph