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From: Mimi Zohar <firstname.lastname@example.org>
To: "Luis R. Rodriguez" <email@example.com>
Cc: linux-wireless <firstname.lastname@example.org>,
Kalle Valo <email@example.com>,
Seth Forshee <firstname.lastname@example.org>,
Johannes Berg <email@example.com>,
Hans de Goede <firstname.lastname@example.org>,
Ard Biesheuvel <email@example.com>,
Peter Jones <firstname.lastname@example.org>,
email@example.com, David Howells <firstname.lastname@example.org>,
Kees Cook <email@example.com>,
Greg Kroah-Hartman <firstname.lastname@example.org>,
Andres Rodriguez <email@example.com>,
Linus Torvalds <firstname.lastname@example.org>,
Andy Lutomirski <email@example.com>
Subject: Re: [PATCH 3/6] firmware: differentiate between signed regulatory.db and other firmware
Date: Wed, 09 May 2018 18:06:57 -0400 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
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.
next prev parent reply other threads:[~2018-05-09 22:06 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-01 13:48 [PATCH 0/6] firmware: kernel signature verification Mimi Zohar
2018-05-01 13:48 ` [PATCH 1/6] firmware: permit LSMs and IMA to fail firmware sysfs fallback loading Mimi Zohar
2018-05-04 0:02 ` Luis R. Rodriguez
2018-05-04 0:36 ` Mimi Zohar
2018-05-01 13:48 ` [PATCH 2/6] ima: prevent sysfs fallback firmware loading Mimi Zohar
2018-05-04 0:06 ` Luis R. Rodriguez
2018-05-01 13:48 ` [PATCH 3/6] firmware: differentiate between signed regulatory.db and other firmware Mimi Zohar
2018-05-04 0:07 ` Luis R. Rodriguez
2018-05-04 0:24 ` Mimi Zohar
2018-05-08 17:34 ` Luis R. Rodriguez
2018-05-09 11:30 ` Mimi Zohar
2018-05-09 19:15 ` Luis R. Rodriguez
2018-05-09 19:57 ` Mimi Zohar
2018-05-09 21:22 ` Luis R. Rodriguez
2018-05-09 22:06 ` Mimi Zohar [this message]
2018-05-09 23:48 ` Luis R. Rodriguez
2018-05-10 2:00 ` Mimi Zohar
2018-05-10 23:26 ` Luis R. Rodriguez
2018-05-11 5:00 ` Mimi Zohar
2018-05-11 21:52 ` Luis R. Rodriguez
2018-05-14 12:58 ` Mimi Zohar
2018-05-14 19:28 ` Luis R. Rodriguez
2018-05-15 2:02 ` Mimi Zohar
2018-05-15 3:26 ` Luis R. Rodriguez
2018-05-15 12:32 ` Josh Boyer
2018-05-15 12:43 ` Mimi Zohar
2018-05-01 13:48 ` [PATCH 4/6] ima: coordinate with signed regulatory.db Mimi Zohar
2018-05-01 13:48 ` [PATCH 5/6] ima: verify kernel firmware signatures when using a preallocated buffer Mimi Zohar
2018-05-01 13:48 ` [RFC PATCH 6/6] ima: prevent loading firmware into a pre-allocated buffer Mimi Zohar
2018-05-04 0:10 ` Luis R. Rodriguez
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