Re: [PATCH v3 0/9] bpf-lsm: Extend interoperability with IMA

Mimi Zohar
2022-03-03T16:05:50Z

[Cc'ing Florent, Kees]

Hi Alexei,

On Wed, 2022-03-02 at 14:20 -0800, Alexei Starovoitov wrote:
> On Wed, Mar 02, 2022 at 12:13:55PM +0100, Roberto Sassu wrote:
> > Extend the interoperability with IMA, to give wider flexibility for the
> > implementation of integrity-focused LSMs based on eBPF.
> >
> > Patch 1 fixes some style issues.
> >
> > Patches 2-6 give the ability to eBPF-based LSMs to take advantage of the
> > measurement capability of IMA without needing to setup a policy in IMA
> > (those LSMs might implement the policy capability themselves).
> >
> > Patches 7-9 allow eBPF-based LSMs to evaluate files read by the kernel.
> >
> > Changelog
> >
> > v2:
> > - Add better description to patch 1 (suggested by Shuah)
> > - Recalculate digest if it is not fresh (when IMA_COLLECTED flag not set)
> > - Move declaration of bpf_ima_file_hash() at the end (suggested by
> > Yonghong)
> > - Add tests to check if the digest has been recalculated
> > - Add deny test for bpf_kernel_read_file()
> > - Add description to tests
> >
> > v1:
> > - Modify ima_file_hash() only and allow the usage of the function with the
> > modified behavior by eBPF-based LSMs through the new function
> > bpf_ima_file_hash() (suggested by Mimi)
> > - Make bpf_lsm_kernel_read_file() sleepable so that bpf_ima_inode_hash()
> > and bpf_ima_file_hash() can be called inside the implementation of
> > eBPF-based LSMs for this hook
> >
> > Roberto Sassu (9):
> > ima: Fix documentation-related warnings in ima_main.c
> > ima: Always return a file measurement in ima_file_hash()
> > bpf-lsm: Introduce new helper bpf_ima_file_hash()
> > selftests/bpf: Move sample generation code to ima_test_common()
> > selftests/bpf: Add test for bpf_ima_file_hash()
> > selftests/bpf: Check if the digest is refreshed after a file write
> > bpf-lsm: Make bpf_lsm_kernel_read_file() as sleepable
> > selftests/bpf: Add test for bpf_lsm_kernel_read_file()
> > selftests/bpf: Check that bpf_kernel_read_file() denies reading IMA
> > policy
>
> We have to land this set through bpf-next.
> Please get the Acks for patches 1 and 2, so we can proceed.

Each year in the LSS integrity status update talk, I've mentioned the
eBPF integrity gaps. I finally reached out to KP, Florent Revest, Kees
and others, letting them know that I'm concerned about the eBPF module
integrity gaps. True there is a difference between signing the eBPF
source modules versus the eBPF generated output, but IMA could at least
verify the integrity of the source eBPF modules making sure they are
measured, the module hash audited, and are properly signed.

Before expanding the ima_file_hash() or ima_inode_hash() usage, I'd
appreciate someone adding the IMA support to measure, appraise, and
audit eBPF modules. I realize that closing the eBPF integrity gaps is
orthogonal to this patch set, but this patch set is not only extending
the ima_file_hash()/ima_inode_hash() usage, but will be used to
circumvent IMA. As per usual, IMA is policy based, allowing those
interested in eBPF module integrity to define IMA policy rules.

thanks,

Mimi