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Subject: Re: [PATCH 04/14] evm: re-release
From: Mimi Zohar <zohar@linux.vnet.ibm.com>
To: Stephen Smalley <sds@tycho.nsa.gov>
Cc: linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org,
       James Morris <jmorris@namei.org>,
       David Safford <safford@watson.ibm.com>,
       Dave Hansen <dave@linux.vnet.ibm.com>, Mimi Zohar <zohar@us.ibm.com>
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On Fri, 2010-06-04 at 10:28 -0400, Stephen Smalley wrote:
> On Wed, 2010-04-21 at 17:49 -0400, Mimi Zohar wrote:
> > EVM protects a file's security extended attributes against integrity
> > attacks. It maintains an HMAC-sha1 value across the extended attributes,
> > storing the value as the extended attribute 'security.evm'. EVM has gone
> > through a number of iterations, initially as an LSM module, subsequently
> > as a LIM integrity provider, and now, when co-located with a security_
> > hook, embedded directly in the security_ hook, similar to IMA.
> > 
> > This is the first part of a local file integrity verification system.
> > While this part does authenticate the selected extended attributes, and
> > cryptographically bind them to the inode, coming extensions will bind
> > other directory and inode metadata for more complete protection.  The
> > set of protected security extended attributes is configured at compile.
> > 
> > EVM depends on the Kernel Key Retention System to provide it with the
> > kernel master key for the HMAC operation.  The kernel master key is
> > securely loaded onto the root's keyring, typically by 'loadkernkey',
> > which either uses the TPM sealed secret key, if available, or a
> > password requested from the console.  To signal EVM, that the key has
> > been loaded onto the keyring, 'echo 1 > <securityfs>/evm'. This is
> > normally done in the initrd, which has already been measured as part
> > of the trusted boot. (Refer to http://linux-ima.sourceforge.net/#EVM.)
> 
> I don't remember this dependency on the kernel key system in prior
> incarnations of EVM.  Can you explain the rationale for using it, and
> the implications?

This changed very early on, so that people without a TPM could 'play'
with it.

Mimi


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