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@xxxxxxxxx/
[2] https://lore.kernel.org/linux-integrity/CAE=NcrbdS-3gVvnnEwdNSOLO
vTenLjyppDz2aJACGRgBYSh=Gw@xxxxxxxxxxxxxx/
Signed-off-by: Raphael Gianotti <raphgi@xxxxxxxxxxxxxxxxxxx>
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
