Re: [PATCH v19 15/20] fsverity: expose verified fsverity built-in signatures to LSMs

Paul Moore
2024-05-30T01:47:10Z

On Fri, May 24, 2024 at 4:46 PM Fan Wu <wufan@linux.microsoft.com> wrote:
>
> This patch enhances fsverity's capabilities to support both integrity and
> authenticity protection by introducing the exposure of built-in
> signatures through a new LSM hook. This functionality allows LSMs,
> e.g. IPE, to enforce policies based on the authenticity and integrity of
> files, specifically focusing on built-in fsverity signatures. It enables
> a policy enforcement layer within LSMs for fsverity, offering granular
> control over the usage of authenticity claims. For instance, a policy
> could be established to permit the execution of all files with verified
> built-in fsverity signatures while restricting kernel module loading
> from specified fsverity files via fsverity digests.
>
> The introduction of a security_inode_setintegrity() hook call within
> fsverity's workflow ensures that the verified built-in signature of a file
> is exposed to LSMs. This enables LSMs to recognize and label fsverity files
> that contain a verified built-in fsverity signature. This hook is invoked
> subsequent to the fsverity_verify_signature() process, guaranteeing the
> signature's verification against fsverity's keyring. This mechanism is
> crucial for maintaining system security, as it operates in kernel space,
> effectively thwarting attempts by malicious binaries to bypass user space
> stack interactions.
>
> The second to last commit in this patch set will add a link to the IPE
> documentation in fsverity.rst.
>
> Signed-off-by: Deven Bowers <deven.desai@linux.microsoft.com>
> Signed-off-by: Fan Wu <wufan@linux.microsoft.com>
>
> ---
> v1-v6:
> + Not present
>
> v7:
> Introduced
>
> v8:
> + Split fs/verity/ changes and security/ changes into separate patches
> + Change signature of fsverity_create_info to accept non-const inode
> + Change signature of fsverity_verify_signature to accept non-const inode
> + Don't cast-away const from inode.
> + Digest functionality dropped in favor of:
> ("fs-verity: define a function to return the integrity protected
> file digest")
> + Reworded commit description and title to match changes.
> + Fix a bug wherein no LSM implements the particular fsverity @name
> (or LSM is disabled), and returns -EOPNOTSUPP, causing errors.
>
> v9:
> + No changes
>
> v10:
> + Rename the signature blob key
> + Cleanup redundant code
> + Make the hook call depends on CONFIG_FS_VERITY_BUILTIN_SIGNATURES
>
> v11:
> + No changes
>
> v12:
> + Add constification to the hook call
>
> v13:
> + No changes
>
> v14:
> + Add doc/comment to built-in signature verification
>
> v15:
> + Add more docs related to IPE
> + Switch the hook call to security_inode_setintegrity()
>
> v16:
> + Explicitly mention "fsverity builtin signatures" in the commit
> message
> + Amend documentation in fsverity.rst
> + Fix format issue
> + Change enum name
>
> v17:
> + Fix various documentation issues
> + Use new enum name LSM_INT_FSVERITY_BUILTINSIG_VALID
>
> v18:
> + Fix typos
> + Move the inode_setintegrity hook call into fsverity_verify_signature()
>
> v19:
> + Cleanup code w.r.t inode_setintegrity hook refactoring
> ---
> Documentation/filesystems/fsverity.rst | 23 +++++++++++++++++++++--
> fs/verity/signature.c | 18 +++++++++++++++++-
> include/linux/security.h | 1 +
> 3 files changed, 39 insertions(+), 3 deletions(-)

Eric, can you give this patch in particular a look to make sure you
are okay with everything? I believe Fan has addressed all of your
previous comments and it would be nice to have your Ack/Review tag if
you are okay with the current revision.

--
paul-moore.com