Re: [PATCH v3 5/7] ima: suspend measurements during buffer copy at kexec execute

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

On 1/11/24 09:30, Mimi Zohar wrote:
> On Fri, 2024-01-05 at 11:50 -0800, Tushar Sugandhi wrote:
>>
>> On 12/20/23 12:44, Mimi Zohar wrote:
>>> On Fri, 2023-12-15 at 17:07 -0800, Tushar Sugandhi wrote:
>>>> If the new measurements are added to the IMA log while it is being
>>>> being copied to the kexec buffer during kexec 'execute', it can miss
>>>> copying those new measurements to the kexec buffer, and the buffer can go
>>>> out of sync with TPM PCRs.  This could result in breaking the integrity
>>>> of the measurements after the kexec soft reboot to the new Kernel.
>>>>
>>>> Add a check in the ima_add_template_entry() function not to measure
>>>> events and return from the function early when 'suspend_ima_measurements'
>>>> flag is set.
>>>>
>>>> This ensures the consistency of the IMA measurement list while copying
>>>> them to the kexec buffer.  When the 'suspend_ima_measurements' flag is
>>>> set, any new measurements will be ignored until the flag is unset.  This
>>>> allows the buffer to be safely copied without worrying about concurrent
>>>> modifications to the measurement list.  This is crucial for maintaining
>>>> the integrity of the measurements during a kexec soft reboot.
>>>>
>>>> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
>>>> ---
>>>>    security/integrity/ima/ima_queue.c | 13 +++++++++++++
>>>>    1 file changed, 13 insertions(+)
>>>>
>>>> diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
>>>> index cb9abc02a304..5946a26a2849 100644
>>>> --- a/security/integrity/ima/ima_queue.c
>>>> +++ b/security/integrity/ima/ima_queue.c
>>>> @@ -195,6 +195,19 @@ int ima_add_template_entry(struct ima_template_entry *entry, int violation,
>>>>    		}
>>>>    	}
>>>>    
>>>> +	/*
>>>> +	 * suspend_ima_measurements will be set if the system is
>>>> +	 * undergoing kexec soft boot to a new kernel.
>>>> +	 * suspending measurements in this short window ensures the
>>>> +	 * consistency of the IMA measurement list during copying
>>>> +	 * of the kexec buffer.
>>>> +	 */
>>>> +	if (atomic_read(&suspend_ima_measurements)) {
>>>> +		audit_cause = "measurements_suspended";
>>>> +		audit_info = 0;
>>>> +		goto out;
>>>> +	}
>>>> +
>>>>    	result = ima_add_digest_entry(entry,
>>>>    				      !IS_ENABLED(CONFIG_IMA_DISABLE_HTABLE));
>>>>    	if (result < 0) {
>>>
>>> I assume you meant to include the suspend/resume code in "ima: kexec:
>>> move ima log copy from kexec load to execute"  in this patch.
>>>
>>
>> Sure, I can move the suspend/resume code from Patch 2/7 of this series
>> to this patch (5/7).
>>
>> Earlier I introduced the suspend/resume functionality in patch 2 because
>> it was used in the functions in that patch.
>>
>> But shifting it hear will make the patches cleaner.
> 
> Just a reminder this isn't the only issued mentioned in 2/7.  Please refer to it
> for the other comments (e.g. make not including/verifying the IMA segment hash a
> separate patch).
> 
> Before reposting, please remember to test after applying each patch in the patch
> set to ensure that the measurement list is properly carried across kexec.

Yes, I had read your responses on patch 2/7.
I have been meaning to respond to you on 2/7, but I kept getting 
distracted by some other work-items on my plate. Really sorry :(

I will respond to your comments on 2/7 by end of the day, and 
incorporate the feedback before reposting.