evm: Load EVM key in ima_load_x509() to avoid appraisal

hulk inclusion
category: feature
feature: IMA Digest Lists extension
bugzilla: 46797

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Public keys do not need to be appraised by IMA as the restriction on the
IMA/EVM keyrings ensures that a key can be loaded only if it is signed with
a key in the primary or secondary keyring.

However, when evm_load_x509() is called, appraisal is already enabled and
a valid IMA signature must be added to the EVM key to pass verification.

Since the restriction is applied on both IMA and EVM keyrings, it is safe
to disable appraisal also when the EVM key is loaded. This patch calls
evm_load_x509() inside ima_load_x509() if CONFIG_IMA_LOAD_X509 is enabled.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>