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

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Message-ID: <8bc74dd8-ecd0-44ad-88a2-8b36fa61100a@linux.microsoft.com>
Date: Thu, 6 Mar 2025 14:45:50 -0800
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 3/5/2025 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

Thanks,

Steven