Re: [PATCH 00/28] security: Move IMA and EVM to the LSM infrastructure

[Roberto Sassu <roberto.sassu@huaweicloud.com>]

On Wed, 2023-03-08 at 10:14 -0500, Mimi Zohar wrote:
> Hi Roberto,
> 
> On Fri, 2023-03-03 at 19:18 +0100, Roberto Sassu wrote:
> > From: Roberto Sassu <roberto.sassu@huawei.com>
> > 
> > This patch set depends on:
> > - https://lore.kernel.org/linux-integrity/20221201104125.919483-1-roberto.sassu@huaweicloud.com/ (there will be a v8 shortly)
> > - https://lore.kernel.org/linux-security-module/20230217032625.678457-1-paul@paul-moore.com/
> > 
> > IMA and EVM are not effectively LSMs, especially due 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.
> > 
> > More specifically, patches 1-13 make IMA and EVM functions suitable to
> > be registered to the LSM infrastructure, by aligning function parameters.
> > 
> > Patches 14-22 add new LSM hooks in the same places where IMA and EVM
> > functions are called, if there is no LSM hook already.
> > 
> > Patch 23 adds the 'last' ordering strategy for LSMs, so that IMA and EVM
> > functions are called in the same order as of today. Also, like with the
> > 'first' strategy, LSMs using it are always enabled, so IMA and EVM
> > functions will be always called (if IMA and EVM are compiled built-in).
> > 
> > Patches 24-27 do the bulk of the work, remove hardcoded calls to IMA and
> > EVM functions, register those functions in the LSM infrastructure, and let
> > the latter call them. In addition, they also reserve one slot for EVM to 
> > supply an xattr to the inode_init_security hook.
> > 
> > Finally, patch 28 removes the rbtree used to bind metadata to the inodes,
> > and instead reserve a space in the inode security blob to store the pointer
> > to metadata. This also brings performance improvements due to retrieving
> > metadata in constant time, as opposed to logarithmic.
> 
> Prior to IMA being upstreamed, it went through a number of iterations,
> first on the security hooks, then as a separate parallel set of
> integrity hooks, and, finally, co-located with the security hooks,
> where they exist.  With this patch set we've come full circle.
> 
> With the LSM stacking support, multiple LSMs can now use the
> 'i_security' field removing the need for the rbtree indirection for
> accessing integrity state info.
> 
> Roberto, thank you for making this change.  Mostly it looks good.  
> Reviewing the patch set will be easier once the prereq's and this patch
> set can be properly applied.

Welcome. Yes, once Paul reviews the other patch set, we can
progressively apply the patches.

Thanks

Roberto