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

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Message-ID: <a952eaa2-faf4-4312-87bd-7cb6a9100df5@linux.microsoft.com>
Date: Tue, 11 Mar 2025 16:45:11 -0700
From: steven chen <chenste@...ux.microsoft.com>
To: Mimi Zohar <zohar@...ux.ibm.com>, Baoquan He <bhe@...hat.com>
Cc: stefanb@...ux.ibm.com, roberto.sassu@...weicloud.com,
 roberto.sassu@...wei.com, eric.snowberg@...cle.com, ebiederm@...ssion.com,
 paul@...l-moore.com, code@...icks.com, bauermann@...abnow.com,
 linux-integrity@...r.kernel.org, kexec@...ts.infradead.org,
 linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org,
 madvenka@...ux.microsoft.com, nramas@...ux.microsoft.com,
 James.Bottomley@...senpartnership.com, vgoyal@...hat.com, dyoung@...hat.com
Subject: Re: [PATCH v9 1/7] ima: copy only complete measurement records across
 kexec

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@...ux.ibm.com>
>>>>>> Signed-off-by: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
>>>>>> Signed-off-by: steven chen <chenste@...ux.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