linux-kernel - Re: IMA: How to manage user space signing policy with others

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Date:	Mon, 04 Mar 2013 20:21:31 -0500
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Eric Paris <eparis@...isplace.org>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	LSM List <linux-security-module@...r.kernel.org>
Subject: Re: IMA: How to manage user space signing policy with others

On Mon, 2013-03-04 at 14:15 -0500, Vivek Goyal wrote:

> I am just brain storming and throwing some ideas and see if soemthing
> makes sense. I agree that allowing one policy only makes it very
> restrictive (while simplifying the implementation).

Agreed, lets try again ...  I think we are actually getting closer.

Without the memory locking or caching issues, would you agree that both
the builtin 'secureboot' and the 'ima_appraise_tcb' policies meet the
secure boot needs?   If both policies are acceptable, then we could
define the builtin 'secureboot' policy as the default policy, which
could be replaced with the 'ima_appraise_tcb' policy, if specified on
the boot command line.  This would eliminate any need for merging of
rules or rule flags.

To address the memory locking and caching issues, we could define a new
extended attribute type called IMA_XATTR_SECURE_BOOT.

enum evm_ima_xattr_type {
        IMA_XATTR_DIGEST = 0x01,
        EVM_XATTR_HMAC,
        EVM_IMA_XATTR_DIGSIG,
};

and set a corresponding flag in iint->flags.  The flag could then be the
bases for setting up any special secureboot requirements, like memory
locking and no caching. 

diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index ddeadc7..6ec1575 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -172,6 +172,8 @@ int ima_appraise_measurement(int func, struct integrity_iint_cache *iint,
 		}
 		status = INTEGRITY_PASS;
 		break;
+	case IMA_XATTR_SECURE_BOOT:
+		iint->flags |= IMA_SB;
 	case EVM_IMA_XATTR_DIGSIG:
 		iint->flags |= IMA_DIGSIG;
 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,

As originally intended, the policy defines which files are appraised,
not how they are appraised.  The extended attribute defines how the file
is to be appraised.

thanks,

Mimi

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