linux-kernel - Re: [PATCH 02/11] evm: Load EVM key in ima_load

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Message-ID: <8a1773d7707639d275fff138736d57472e26ade5.camel@linux.ibm.com>
Date:   Fri, 21 Aug 2020 14:45:14 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>, mjg59@...gle.com
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/11] evm: Load EVM key in ima_load_x509() to avoid
 appraisal

On Thu, 2020-06-18 at 18:01 +0200, Roberto Sassu wrote:
> Public keys do not need to be appraised by IMA as the restriction on the
> IMA/EVM keyrings ensures that a key is loaded only if it is signed with a
> key in the primary or secondary keyring.
> 
> However, when evm_load_x509() is loaded, 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 defined.
> 
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> ---
>  security/integrity/iint.c         | 2 ++
>  security/integrity/ima/ima_init.c | 4 ++++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/security/integrity/iint.c b/security/integrity/iint.c
> index e12c4900510f..4765a266ba96 100644
> --- a/security/integrity/iint.c
> +++ b/security/integrity/iint.c
> @@ -212,7 +212,9 @@ int integrity_kernel_read(struct file *file, loff_t offset,
>  void __init integrity_load_keys(void)
>  {
>  	ima_load_x509();
> +#ifndef CONFIG_IMA_LOAD_X509
>  	evm_load_x509();
> +#endif
>  }
>  
>  static int __init integrity_fs_init(void)
> diff --git a/security/integrity/ima/ima_init.c b/security/integrity/ima/ima_init.c
> index 4902fe7bd570..9d29a1680da8 100644
> --- a/security/integrity/ima/ima_init.c
> +++ b/security/integrity/ima/ima_init.c
> @@ -106,6 +106,10 @@ void __init ima_load_x509(void)
>  
>  	ima_policy_flag &= ~unset_flags;
>  	integrity_load_x509(INTEGRITY_KEYRING_IMA, CONFIG_IMA_X509_PATH);
> +
> +	/* load also EVM key to avoid appraisal */
> +	evm_load_x509();
> +
>  	ima_policy_flag |= unset_flags;
>  }
>  #endif

As much as possible IMA and EVM should remain independent of each
other.   Modifying integrity_load_x509() doesn't help.  This looks like
a good reason for calling another EVM function from within IMA.

Mimi