Re: [PATCH v4 7/7] ima: measure kexec load and exec events as critical data

[Mimi Zohar <zohar@linux.ibm.com>]

On Mon, 2024-01-22 at 10:38 -0800, Tushar Sugandhi wrote:

The problem statement could be written as:

The amount of memory allocated at kexec load, even with the extra memory
allocated, might not be large enough for the entire measurement list.  The
indeterminate interval between kexec 'load' and 'execute' could exacerbate this
problem.

Mimi

> There could be a potential mismatch between IMA measurements and TPM PCR
> quotes caused by the indeterminate interval between kexec 'load' and
> 'execute'.  The extra memory allocated at kexec 'load' for IMA log buffer
> may run out.  It can lead to missing events in the IMA log after a soft
> reboot to the new Kernel, resulting in TPM PCR quotes mismatch and remote
> attestation failures.
> 
> Define two new IMA events, 'kexec_load' and 'kexec_execute', to be 
> measured as critical data at kexec 'load' and 'execute' respectively.
> Report the allocated kexec segment size, IMA binary log size and the
> runtime measurements count as part of those events.
> 
> These events, and the values reported through them, serve as markers in
> the IMA log to verify the IMA events are captured during kexec soft
> reboot.  The presence of a 'kexec_load' event in between the last two
> 'boot_aggregate' events in the IMA log implies this is a kexec soft
> reboot, and not a cold-boot. And the absence of 'kexec_execute' event
> after kexec soft reboot implies missing events in that window which
> results in inconsistency with TPM PCR quotes, necessitating a cold boot
> for a successful remote attestation.
> 
> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>