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

[Tushar Sugandhi <tusharsu@linux.microsoft.com>]

On 1/24/24 06:35, Mimi Zohar wrote:
> 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
> 
Thank you again for taking efforts to write one more example for me.
Appreciate it.

Will do.

~Tushar

>> 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>
> 
>