On Wed, 2018-05-09 at 21:22 +0000, Luis R. Rodriguez wrote: > On Wed, May 09, 2018 at 03:57:18PM -0400, Mimi Zohar wrote: > > On Wed, 2018-05-09 at 19:15 +0000, Luis R. Rodriguez wrote: > > > > > > > > If both are enabled, do we require both signatures or is one enough. > > > > > > > > > > Good question. Considering it as a stacked LSM (although not implemented > > > > > as one), I'd say its up to who enabled the Kconfig entries. If IMA and > > > > > CONFIG_CFG80211_REQUIRE_SIGNED_REGDB are enabled then both. If someone enabled > > > > > IMA though, then surely I agree that enabling > > > > > CONFIG_CFG80211_REQUIRE_SIGNED_REGDB is stupid and redundant, but its up to the > > > > > system integrator to decide. > > > > > > > > Just because IMA-appraisal is enabled in the kernel doesn't mean that > > > > firmware signatures will be verified. That is a run time policy > > > > decision. > > > > > > Sure, I accept this if IMA does not do signature verification. However > > > signature verification seems like a stackable LSM decision, no? > > > > IMA-appraisal can be configured to enforce file signatures. Refer to > > discussion below as to how. > > > > > > > If we however want to make it clear that such things as > > > > > CONFIG_CFG80211_REQUIRE_SIGNED_REGDB are not required when IMA is enabled we > > > > > could just make the kconfig depend on !IMA or something? Or perhaps a new > > > > > kconfig for IMA which if selected it means that drivers can opt to open code > > > > > *further* kernel signature verification, even though IMA already is sufficient. > > > > > Perhaps CONFIG_ENABLE_IMA_OVERLAPPING, and the driver depends on it? > > > > > > > > The existing CONFIG_IMA_APPRAISE is not enough. If there was a build > > > > time IMA config that translated into an IMA policy requiring firmware > > > > signature verification (eg. CONFIG_IMA_APPRAISE_FIRMWARE), this could > > > > be sorted out at build time. > > > > > > I see makes sense. > > > > Ok, so instead of introducing READING_FIRMWARE_REGULATORY_DB, I'll > > post patches introducing CONFIG_IMA_APPRAISE_FIRMWARE, as described > > above. > > OK, its still not clear to what it will do. If it does not touch the firmware > loader code, and it just sets and configures IMA to do file signature checking > on its own, then yes I think both mechanisms would be doing the similar work. > > Wouldn't IMA do file signature checks then for all files? Or it would just > enable this for whatever files userspace wishes to cover? Enabling CONFIG_IMA_APPRAISE_FIRMWARE would enforce firmware signatures on all directly loaded firmware and fail any method of loading firmware that the signature couldn't be verified. > One of the things with READING_FIRMWARE_REGULATORY_DB is to also use and trust > the wireless-regdgb maintainer's key for this file, could IMA be configured to > do that? IMA has its own trusted keyring. So either the maintainer's key would need to be added to the IMA keyring, or IMA-appraisal would need to use the regdb keyring. > Because that would be one difference here. The whole point of adding > CONFIG_CFG80211_REQUIRE_SIGNED_REGDB was to replace CRDA which is a userspace > component which checks the signature of regulatory.db before reading it and > passing data to the kernel from it. > > Now, however silly it may be to have CONFIG_IMA_APPRAISE_FIRMWARE *and* > CONFIG_CFG80211_REQUIRE_SIGNED_REGDB, is your intent in this new patch set > you are mentioning, to still enable both to co-exist? At build, either CONFIG_CFG80211_REQUIRE_SIGNED_REGDB or CONFIG_IMA_APPRAISE_FIRMWARE, where IMA is appraising all firwmare, would be enabled, not both. The builtin IMA-policies could be replaced with a custom policy, requiring firmware signature verification. In that case, the regdb signature would be verified twice. > > > > > > > Assigning a different id for regdb signed firmware allows LSMs and IMA > > > > > > to handle regdb files differently. > > > > > > > > > > That's not the main concern here, its the precedent we are setting here for > > > > > any new kernel interface which open codes firmware signing on its own. What > > > > > you are doing means other kernel users who open codes their own firmware > > > > > signing may need to add yet-another reading ID. That doesn't either look > > > > > well on code, and seems kind of silly from a coding perspective given > > > > > the above, in which I clarify IMA still is doing its own appraisal on it. > > > > > > > > Suppose, > > > > > > > > 1. Either CONFIG_CFG80211_REQUIRE_SIGNED_REGDB or > > > > "CONFIG_IMA_APPRAISE_FIRMWARE" would be configured at build. > > > > > > > > 2. If CONFIG_CFG80211_REQUIRE_SIGNED_REGDB is configured, not > > > > "CONFIG_IMA_APPRAISE_FIRMWARE", a custom IMA-policy rule that > > > > appraises the firmware signature could be defined. In this case, both > > > > signature verification methods would be enforced. > > > > > > > > then READING_FIRMWARE_REGULATORY_DB would not be needed. > > > > > > True, however I'm suggesting that CONFIG_CFG80211_REQUIRE_SIGNED_REGDB > > > could just be a mini subsystem stackable LSM. > > > > Yes, writing regdb as a micro/mini LSM sounds reasonable. The LSM > > would differentiate between other firmware and the regulatory.db based > > on the firmware's pathname. > > If that is the only way then it would be silly to do the mini LSM as all > calls would have to have the check. A special LSM hook for just the > regulatory db also doesn't make much sense. All calls to request_firmware() are already going through this LSM hook. I should have said, it would be based on both READING_FIRMWARE and the firmware's pathname. > > > Making regdb an LSM would have the same issues as currently - deciding > > if regdb, IMA-appraisal, or both verify the regdb's signature. > > Its unclear to me why they can't co-exist yet and not have to touch > the firmware_loader code at all. With the changes discussed above, they will co-exist. Other than the Kconfig changes, I don't think it will touch the firmware_loader code. Mimi
