Re: [PATCH v4 00/23] security: Move IMA and EVM to the LSM infrastructure

[Mimi Zohar <zohar@linux.ibm.com>]

On Fri, 2023-10-27 at 10:35 +0200, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@huawei.com>
> 
> IMA and EVM are not effectively LSMs, especially due to the fact that in
> the past they could not provide a security blob while there is another LSM
> active.
> 
> That changed in the recent years, the LSM stacking feature now makes it
> possible to stack together multiple LSMs, and allows them to provide a
> security blob for most kernel objects. While the LSM stacking feature has
> some limitations being worked out, it is already suitable to make IMA and
> EVM as LSMs.
> 
> In short, while this patch set is big, it does not make any functional
> change to IMA and EVM. IMA and EVM functions are called by the LSM
> infrastructure in the same places as before (except ima_post_path_mknod()),
> rather being hardcoded calls, and the inode metadata pointer is directly
> stored in the inode security blob rather than in a separate rbtree.
> 
> To avoid functional changes, it was necessary to keep the 'integrity' LSM
> in addition to the newly introduced 'ima' and 'evm' LSMs, despite there is
> no LSM ID assigned to it. There are two reasons: first, IMA and EVM still
> share the same inode metadata, and thus cannot directly reserve space in
> the security blob for it; second, someone needs to initialize 'ima' and
> 'evm' exactly in this order, as the LSM infrastructure cannot guarantee
> that.
> 
> The patch set is organized as follows.
> 
> Patches 1-9 make IMA and EVM functions suitable to be registered to the LSM
> infrastructure, by aligning function parameters.
> 
> Patches 10-18 add new LSM hooks in the same places where IMA and EVM
> functions are called, if there is no LSM hook already.
> 
> Patches 19-22 do the bulk of the work, introduce the new LSMs 'ima' and
> 'evm', and move hardcoded calls to IMA, EVM and integrity functions to
> those LSMs. In addition, they reserve one slot for the 'evm' LSM to supply
> an xattr with the inode_init_security hook.
> 
> Finally, patch 23 removes the rbtree used to bind integrity metadata to the
> inodes, and instead reserves a space in the inode security blob to store
> the pointer to that metadata. This also brings performance improvements due
> to retrieving metadata in constant time, as opposed to logarithmic.
> 
> The patch set applies on top of lsm/next-queue, commit 0310640b00d2 ("lsm:
> don't yet account for IMA in LSM_CONFIG_COUNT calculation"), plus commits
> in linux-integrity/next-integrity-testing up to bc4532e9cd3b ("ima: detect
> changes to the backing overlay file").

Thanks, Roberto!  The patch set looks really good.  I just sent a few
very minor comments.

Mimi