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SubjectRe: [RESEND][PATCH] Documentation: added order requirement for ima_hash=
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On 2022/1/26 9:07, Mimi Zohar wrote:
> On Tue, 2022-01-25 at 17:02 +0800, GUO Zihua wrote:
>> From: Guo Zihua <guozihua@huawei.com>
>>
>> Commandline parameter ima_hash= and ima_template= has order requirement
>> for them to work correctly together. Namely ima_hash= must be
>> specified after ima_template=, otherwise ima_template= will be ignored.
>>
>> The reason is that when handling ima_hash=, ima template would be set to
>> the default value if it has not been initialized already, and that value
>> cannot be changed afterwards by ima_template=.
>>
>> This patch adds this limitation to the documentation.
>>
>> Reviewed-by: Roberto Sassu <roberto.sassu@huawei.com>
>> Signed-off-by: Guo Zihua <guozihua@huawei.com>
>
> This issue should be limited to the original "ima" template format,
> which only supports hash algorithms of 20 bytes or less. The "ima_ng"
> template has been the default since larger digests and templates were
> upstreamed back in Linux 3.13[1]. Do you really still have kernels
> built with the original "ima" template?
>
> [1] Refer to commit 4286587dccd4 ("ima: add Kconfig default measurement
> list template").
>
> thanks,
>
> Mimi

Hi Mimi,

The issue is that if ima_hash is specified before ima_template,
ima_template will not work. Built-in default only affects which template
will be loaded eventually.

For example, if the built-in default template is ima-ng and user would
like to change it to ima-sig with sha512 by specifying "ima_hash=sha512
ima_template=ima-sig" in command line, the result will be ima-ng with
sha512, not ima-sig with sha512.

--
Best
GUO Zihua

>
>> ---
>> Documentation/admin-guide/kernel-parameters.txt | 7 +++++++
>> 1 file changed, 7 insertions(+)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index f5a27f067db9..1b5aa6ca65f8 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -1843,6 +1843,10 @@
>> The list of supported hash algorithms is defined
>> in crypto/hash_info.h.
>>
>> + This parameter must be specified after ima_template=,
>> + as it would set the default template and that cannot be
>> + changed by ima_template= afterwards.
>> +
>> ima_policy= [IMA]
>> The builtin policies to load during IMA setup.
>> Format: "tcb | appraise_tcb | secure_boot |
>> @@ -1879,6 +1883,9 @@
>> Formats: { "ima" | "ima-ng" | "ima-sig" }
>> Default: "ima-ng"
>>
>> + This parameter must be specified before ima_hash=.
>> + Please refer to ima_hash= for further explanation.
>> +
>> ima_template_fmt=
>> [IMA] Define a custom template format.
>> Format: { "field1|...|fieldN" }
>
>
> .

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