Re: [PATCH v3 3/3] ima: Add support for staging measurements for deletion

[steven chen <chenste@linux.microsoft.com>]

On 3/20/2026 10:26 AM, Roberto Sassu wrote:
> On Fri, 2026-03-20 at 10:24 -0700, steven chen wrote:
>> On 3/20/2026 10:10 AM, Roberto Sassu wrote:
>>> On Fri, 2026-03-20 at 09:58 -0700, steven chen wrote:
>>>> On 3/20/2026 5:41 AM, Mimi Zohar wrote:
>>>>> On Thu, 2026-03-19 at 14:31 -0700, steven chen wrote:
>>>>>
>>>>>>> - Support for deleting N measurement records (and pre-pending the remaining
>>>>>>> measurement records)
>>>>>> Is there any problem to bring work of "stage" step together to the
>>>>>> deletion step?
>>>>>>
>>>>>> "Trim N" method does everything that "staged" method can do, right?
>>>>>> what's the "stage" method can do but "trim N" method can't do?
>>>>>>
>>>>>> in user space, if in "staged" state, no other user space agent can
>>>>>> access the IMA measure list, right?
>>>>>>
>>>>>> Could you explain the benefit of bringing the "stage" step?
>>>>> The performance improvement is because "staging" the IMA measurement list takes
>>>>> the lock in order to move the measurement list pointer and then releases it.
>>>>> New measurements can then be appended to a new measurement list.  Deleting
>>>>> records is done without taking the lock to walk the staged measurement list.
>>>>>
>>>>> Without staging the measurement list, walking the measurement list to trim N
>>>>> records requires taking and holding the lock.  The performance is dependent on
>>>>> the size of the measurement list.
>>>>>
>>>>> Your question isn't really about "staging" the measurement list records, but
>>>>> requiring a userspace signal to delete them.  To answer that question, deleting
>>>>> N records (third patch) could imply staging all the measurement records and
>>>>> immediately deleting N records without an explicit userspace signal.
>>>>>
>>>>> I expect the requested "documentation" patch will provide the motivation for the
>>>>> delayed deletion of the measurement list.
>>>>>
>>>>> Mimi
>>>> "Staging" is great on reducing kernel IMA measurement list locking time.
>>>>
>>>> How about just do "stage N" entries and then delete the staged list in
>>>> one shot?
>>>> It means merge two APIs into one API
>>>>        int ima_queue_stage(void)
>>>>        int ima_queue_delete_staged(unsigned long req_value)
>>>>
>>>> The kernel lock time will be the same. And user space lock time will be
>>>> reduced.
>>> It is not the same. The walk on the staged list is done without holding
>>> ima_extend_list_mutex.
>>>
>>> Roberto
>> Is it possible to merge two APIs work into one API?
>>        int ima_queue_stage(void)
>>        int ima_queue_delete_staged(unsigned long req_value)
> It will be done transparently for the user. IMA will call both
> functions for the same securityfs write.
>
> Roberto

If merge two APIs into one API, it will reduce user space measurement
list lock time.
Thanks,
Steven