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    SubjectRe: [PATCH 04/14] evm: re-release
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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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