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

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Date:   Mon, 31 Aug 2020 09:44:20 +0000
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>,
        "mjg59@...gle.com" <mjg59@...gle.com>
CC:     "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Silviu Vlasceanu <Silviu.Vlasceanu@...wei.com>
Subject: RE: [PATCH 02/11] evm: Load EVM key in ima_load_x509() to avoid
 appraisal

> From: Mimi Zohar [mailto:zohar@...ux.ibm.com]
> Sent: Friday, August 21, 2020 8:45 PM
> 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.

Can I add your Reviewed-by?

Thanks

Roberto

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