On Wed, 2018-03-07 at 11:41 -0800, James Bottomley wrote:

On Wed, 2018-03-07 at 14:21 -0500, Mimi Zohar wrote:

quoted

On Wed, 2018-03-07 at 11:08 -0800, James Bottomley wrote:

quoted

On Wed, 2018-03-07 at 13:55 -0500, Mimi Zohar wrote:

quoted

On Wed, 2018-03-07 at 11:51 -0700, Jason Gunthorpe wrote:

quoted

On Tue, Mar 06, 2018 at 11:26:26PM -0600, Jiandi An wrote:

quoted

TPM_CRB driver is the TPM support for ARM64.??If it
is built as module, TPM chip is registered after IMA
init.??tpm_pcr_read() in IMA driver would fail and
display the following message even though eventually
there is TPM chip on the system:

ima: No TPM chip found, activating TPM-bypass! (rc=-19)

Fix IMA Kconfig to select TPM_CRB so TPM_CRB driver is
built in kernel and initializes before IMA driver.

Signed-off-by: Jiandi An <redacted>
?security/integrity/ima/Kconfig | 1 +
?1 file changed, 1 insertion(+)

diff --git a/security/integrity/ima/Kconfig

b/security/integrity/ima/Kconfig
index 35ef693..6a8f677 100644

+++ b/security/integrity/ima/Kconfig

@@ -10,6 +10,7 @@ config IMA

?	select CRYPTO_HASH_INFO
?	select TCG_TPM if HAS_IOMEM && !UML
?	select TCG_TIS if TCG_TPM && X86

Well, this explains why IMA doesn't work on one of my X86 systems:
it's got a non i2c infineon TPM.

quoted

quoted

quoted

+	select TCG_CRB if TCG_TPM && ACPI
?	select TCG_IBMVTPM if TCG_TPM && PPC_PSERIES
?	help
?	??The Trusted Computing Group(TCG) runtime Integrity

This seems really weird, why are any specific TPM drivers
linked to IMA config, we have lots of drivers..

I don't think I've ever seen this pattern in Kconfig before?

As you've seen by the current discussions, the TPM driver needs
to be initialized prior to IMA. ?Otherwise IMA goes into TPM-
bypass mode. ?That implies that the TPM must be builtin to the
kernel, and not as a kernel module.

Actually, that's not necessarily true: ?If we don't begin appraisal
until after the initrd phase, then the initrd can load TPM modules
before IMA starts.

This would involve a bit of code rejigging to not require a TPM
until IMA wants to write its first measurement, but it looks doable
and would get us out of having to second guess TPM selections.

The question is about measurement, not appraisal. ?Although the
initramfs might be measured, the initramfs can access files on the
real root filesystem. ?Those files need to be measured, before they
are used/accessed.

Isn't it a question of threat model? ?Because the initrd is measured,
you know it's the one you specified and you should know its security
properties, so measurement doesn't really need to begin until the root
pivots.

Perhaps in the case where the initramfs is signed and the signature is
verified, I would agree that I know the security properties of the
initramfs. ?That still doesn't negate the fact that the initramfs
could access files on real root, without first measuring them.

At that point you pick up the boot aggregate so the log now is
tied to the initrd measurement. ?Conversely, I can't really see a
threat model where you could trick a correctly measured initrd into
subverting IMA, especially because listening network daemons aren't
usually active at this stage.

Linux based boot loaders can be configured to download remote kernel
images and initramfs files - network boot.

I'm not saying there isn't a use case for wanting your TPM built in,
I'm just saying I don't think it needs to be required for everyone who
uses IMA.

If the TPM module is not builtin, there are no guarantees when it was
loaded. ?There could be a disconnect between the IMA measurement list
and the TPM PCRs.

If someone has a special use case, then I agree with you, that we
could theoretically support it, but I don't think we want to confuse
distros or anyone else. ?The TPM should be builtin, so that IMA
measurements can begin before accessing real root.

Mimi

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