Re: [PATCH v5 03/21] evm: re-release
From: Mimi Zohar
Date: Fri May 20 2011 - 07:22:03 EST
On Fri, 2011-05-20 at 13:12 +0200, Harald Hoyer wrote:
> Am 20.05.2011 00:49, schrieb Mimi Zohar:
> > On Thu, 2011-05-19 at 01:05 -0500, Serge E. Hallyn wrote:
> >> Quoting Mimi Zohar (zohar@xxxxxxxxxxxxxxxxxx):
> >>> EVM protects a file's security extended attributes(xattrs) against integrity
> >>> attacks. This patchset provides the framework and an initial method. The
> >>> initial method maintains an HMAC-sha1 value across the security extended
> >>> attributes, storing the HMAC value as the extended attribute 'security.evm'.
> >>> Other methods of validating the integrity of a file's metadata will be posted
> >>> separately (eg. EVM-digital-signatures).
> >>> While this patchset does authenticate the security xattrs, and
> >>> cryptographically binds them to the inode, coming extensions will bind other
> >>> directory and inode metadata for more complete protection. To help simplify
> >>> the review and upstreaming process, each extension will be posted separately
> >>> (eg. IMA-appraisal, IMA-appraisal-directory). For a general overview of the
> >>> proposed Linux integrity subsystem, refer to Dave Safford's whitepaper:
> >>> http://downloads.sf.net/project/linux-ima/linux-ima/Integrity_overview.pdf.
> >>> EVM depends on the Kernel Key Retention System to provide it with a
> >>> trusted/encrypted key for the HMAC-sha1 operation. The key is loaded onto the
> >>> root's keyring using keyctl. Until EVM receives notification that the key has
> >>> been successfully loaded onto the keyring (echo 1 > <securityfs>/evm), EVM can
> >>> not create or validate the 'security.evm' xattr, but returns INTEGRITY_UNKNOWN.
> >>> Loading the key and signaling EVM should be done as early as possible. Normally
> >>> this is done in the initramfs, which has already been measured as part of the
> >>> trusted boot. For more information on creating and loading existing
> >>> trusted/encrypted keys, refer to Documentation/keys-trusted-encrypted.txt. A
> >>> sample dracut patch, which loads the trusted/encrypted key and enables EVM, is
> >>> available from http://linu-ima.sourceforge.net/#EVM.
> >> That should read http://linux-ima.sourceforge.net/#EVM.
> > Thanks for catching that.
> The dracut patch, could easily turned into a separate dracut module with its own
> files, without patching. Somebody did not understand the modular nature of
> dracut. While you are at it, I happily integrate that module in upstream, if you
> submit it to the initramfs mailing list.
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