Re: [PATCH v9 1/7] ima: copy only complete measurement records across kexec

steven chen
2025-03-11T23:45:12Z

On 3/11/2025 5:44 AM, Mimi Zohar wrote:
> On Thu, 2025-03-06 at 21:51 -0500, Mimi Zohar wrote:
>> On Thu, 2025-03-06 at 14:45 -0800, steven chen wrote:
>>> On 3/5/2025 4:27 AM, Mimi Zohar wrote:
>>>> On Wed, 2025-03-05 at 20:08 +0800, Baoquan He wrote:
>>>>> On 03/04/25 at 11:03am, steven chen wrote:
>>>>>> Carrying the IMA measurement list across kexec requires allocating a
>>>>>> buffer and copying the measurement records. Separate allocating the
>>>>>> buffer and copying the measurement records into separate functions in
>>>>>> order to allocate the buffer at kexec 'load' and copy the measurements
>>>>>> at kexec 'execute'.
>>>>>>
>>>>>> This patch includes the following changes:
>>>>> I don't know why one patch need include so many changes. From below log,
>>>>> it should be split into separate patches. It may not need to make one
>>>>> patch to reflect one change, we should at least split and wrap several
>>>>> kind of changes to ease patch understanding and reviewing. My personal
>>>>> opinion.
>>>> Agreed, well explained.
>>>>
>>>> Mimi
>>>>
>>>>>> - Refactor ima_dump_measurement_list() to move the memory allocation
>>>>>> to a separate function ima_alloc_kexec_file_buf() which allocates
>>>>>> buffer of size 'kexec_segment_size' at kexec 'load'.
>>>>>> - Make the local variable ima_kexec_file in ima_dump_measurement_list()
>>>>>> a local static to the file, so that it can be accessed from
>>>>>> ima_alloc_kexec_file_buf(). Compare actual memory required to ensure
>>>>>> there is enough memory for the entire measurement record.
>>>>>> - Copy only complete measurement records.
>>>>>> - Make necessary changes to the function ima_add_kexec_buffer() to call
>>>>>> the above two functions.
>>>>>> - Compared the memory size allocated with memory size of the entire
>>>>>> measurement record. Copy only complete measurement records if there
>>>>>> is enough memory. If there is not enough memory, it will not copy
>>>>>> any IMA measurement records, and this situation will result in a
>>>>>> failure of remote attestation.
>>>>>>
>>>>>> Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
>>>>>> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
>>>>>> Signed-off-by: steven chen <chenste@linux.microsoft.com>
>>> I will split this patch into the following two patches:
>>>
>>>     ima: define and call ima_alloc_kexec_file_buf
>>>     ima: copy measurement records as much as possible across kexec
>> Steven, breaking up code into patches is in order to simplify patch review.
>> This is done by limiting each patch to a single "logical change" [1]. For
>> example, the change below has nothing to do with "separate allocating the buffer
>> and copying the measurement records into separate functions".
>>
>> /* This is an append-only list, no need to hold the RCU read lock */
>> list_for_each_entry_rcu(qe, &ima_measurements, later, true) {
>> - if (file.count < file.size) {
>> + entry_size += ima_get_binary_runtime_entry_size(qe->entry);
>> + if (entry_size <= segment_size) {
>> khdr.count++;
>> - ima_measurements_show(&file, qe);
>> + ima_measurements_show(&ima_kexec_file, qe);
>> } else {
>> ret = -EINVAL;
>> + pr_err("IMA log file is too big for Kexec buf\n");
>> break;
>> }
>> }
>>
>> The original code potentially copied a partial last measurement record, not a
>> complete measurement record. For ease of review, the above change is fine, but
>> it needs to be a separate patch.
>>
>> Patches:
>> 1. ima: copy only complete measurement records across kexec
>> 2. ima: define and call ima_alloc_kexec_file_buf()
> Steven,
>
> The alternative would be to revert using ima_get_binary_runtime_entry_size() and
> simply use "ima_kexec_file.count < ima_kexec_file.size". Only
> ima_kexec_file.size would be initialized in ima_alloc_kexec_buf(). The rest
> would remain in ima_dump_measurement_list(). get_binary_runtime_size() wouldn't
> need to be made global.
>
> To further simplify the patch review, first define a separate patch to just
> rename the seq_file "file" to "ima_kexec_file".
>
> Mimi

Hi Mimi,

I will work on it.

Thanks,

Steven