Re: [PATCH 1/3] ima: Add TCB policy as an example

[Petr Vorel <pvorel@suse.cz>]

Hi Mimi,

> Hi Petr,

> On Tue, 2024-11-26 at 18:38 +0100, Petr Vorel wrote:
> > Signed-off-by: Petr Vorel <pvorel@suse.cz>

> Except for the "dont_measure <tmpfs>" rule, the "dont_measure" rules are for
> pseudo filesystems.  Including a "dont_measure <tmpfs>" policy rule was suppose
> to be limited to the initramfs, and then replaced with an IMA custom policy. I
> would either re-order the rules so that the "dont_measure" rules are only before
> the two "func=FILE_CHECK" rules or perhaps remove the "dont_measure <tmpfs>"
> policy rule.  The kernel builtin "tcb" policy should be updated as described
> below.


> > ---
> >  .../ima/datafiles/ima_measurements/tcb.policy | 20 +++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> >  create mode 100644 testcases/kernel/security/integrity/ima/datafiles/ima_measurements/tcb.policy

> > diff --git a/testcases/kernel/security/integrity/ima/datafiles/ima_measurements/tcb.policy b/testcases/kernel/security/integrity/ima/datafiles/ima_measurements/tcb.policy
> > new file mode 100644
> > index 0000000000..280e6af87c
> > --- /dev/null
> > +++ b/testcases/kernel/security/integrity/ima/datafiles/ima_measurements/tcb.policy
> > @@ -0,0 +1,20 @@
> > +dont_measure fsmagic=0x9fa0
> > +dont_measure fsmagic=0x62656572
> > +dont_measure fsmagic=0x64626720
> > +dont_measure fsmagic=0x1021994
> > +dont_measure fsmagic=0x1cd1
> > +dont_measure fsmagic=0x42494e4d
> > +dont_measure fsmagic=0x73636673
> > +dont_measure fsmagic=0xf97cff8c
> > +dont_measure fsmagic=0x43415d53
> > +dont_measure fsmagic=0x27e0eb
> > +dont_measure fsmagic=0x63677270
> > +dont_measure fsmagic=0x6e736673
> > +dont_measure fsmagic=0xde5e81e4

> Limit the affect of "dont_measure" rules to just the "func=FILE_CHECK" rules, by
> moving them to before the "func=FILE_CHECK" rules.

> > +measure func=MMAP_CHECK mask=MAY_EXEC
> > +measure func=BPRM_CHECK mask=MAY_EXEC
> > +measure func=FILE_CHECK mask=^MAY_READ euid=0
> > +measure func=FILE_CHECK mask=^MAY_READ uid=0

> Move above two "func=FILE_CHECK" rules to the end.

> > +measure func=MODULE_CHECK
> > +measure func=FIRMWARE_CHECK
> > +measure func=POLICY_CHECK

Thanks for your comments. You probably mean ima_policy=tcb from [1], right?

dont_measure fsmagic=0x9fa0          # PROC_SUPER_MAGIC
dont_measure fsmagic=0x62656572      # SYSFS_MAGIC
dont_measure fsmagic=0x64626720      # DEBUGFS_MAGIC
dont_measure fsmagic=0x1021994       # TMPFS_MAGIC
dont_measure fsmagic=0x1cd1          # DEVPTS_SUPER_MAGIC
dont_measure fsmagic=0x42494e4d      # BINFMTFS_MAGIC
dont_measure fsmagic=0x73636673      # SECURITYFS_MAGIC
dont_measure fsmagic=0xf97cff8c      # SELINUX_MAGIC
dont_measure fsmagic=0x43415d53      # SMACK_MAGIC
dont_measure fsmagic=0x27e0eb        # CGROUP_SUPER_MAGIC
dont_measure fsmagic=0x63677270      # CGROUP2_SUPER_MAGIC
dont_measure fsmagic=0x6e736673      # NSFS_MAGIC
dont_measure fsmagic=0xde5e81e4      # EFIVARFS_MAGIC
measure func=MMAP_CHECK mask=MAY_EXEC
measure func=BPRM_CHECK mask=MAY_EXEC           # binary executed
measure func=FILE_CHECK mask=^MAY_READ euid=0
measure func=FILE_CHECK mask=^MAY_READ uid=0    # root opened r/o, r/w
measure func=MODULE_CHECK
measure func=FIRMWARE_CHECK
measure func=POLICY_CHECK

without: dont_measure fsmagic=0x1021994       # TMPFS_MAGIC
(I would remove the comments from final policy file)

Or if not, feel free to send a patch with optimal policy.

Kind regards,
Petr

[1] https://ima-doc.readthedocs.io/en/latest/ima-policy.html#ima-tcb

> thanks,

> Mimi