Re: [tpm2] Issues experimenting with tpm2-tools and keyctl trusted keys

[Thibaut Sautereau <thibaut.sautereau at clip-os.org>]

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Hello Javier,

On Wed, Jan 23, 2019 at 10:36:22AM +0100, Javier Martinez Canillas wrote:
> Hello Thibaut,
> 
> On 1/21/19 9:16 AM, Thibaut Sautereau wrote:
> > Hello folks,
> > 
> > I'm experimenting with TPM 2.0 (using swtpm 0.1.0), tpm2-tools 3.1.3,
> > tpm2-tss 2.1.0 and the Linux 4.19.16 kernel's trusted keys. I found this
> > thread [1] about the "policydigest" and "policyhandle" options added to
> > keyctl but I cannot reproduce the given example [2] using tpm2-tools
> > instead of the author's Python testing scripts [3]. I wonder if I do
> > something wrong by executing the following commands:
> >
> 
> Did it work for you when using Jarkko's test scripts?

Yes, it did.

> > export TPM2TOOLS_TCTI="device:/dev/tpmrm0"
> > tpm2_takeownership --clear
> > # I tried fiddling with the object attributes in the following command
> > # but AIUI the default ones should be OK
> > tpm2_createprimary --hierarchy=o --halg=sha256 --kalg=rsa \
> > 	--context=/tmp/primary.context 
> > tpm2_evictcontrol --auth=o --context=/tmp/primary.context \
> > 	--handle=0x80ffffff --persistent=0x81010001
> > tpm2_createpolicy --policy-file=/tmp/policy.digest --policy-pcr \
> > 	--set-list=sha256:0 --policy-digest-alg=sha256
> > policydigest=$(xxd -p /tmp/policy.digest | tr -d '\n')
> > keyid=$(keyctl add trusted test \
> > 	"new 32 keyhandle=0x81010001 hash=sha256 policydigest=$policydigest" @u)
> > keyctl link @us @s
> > keyctl pipe $keyid > /tmp/blob.hex
> > 
> > Until here, everything works fine.
> > 
> > Now for testing I want to reimport the key from the blob file, but I
> > need a handle to a TPM_SE_POLICY and thus need to directly use the TPM
> > device, as the in-kernel resource manager I was using so far would
> > prevent me from keeping a policy session "opened". So I re-export
> > TPM2TOOLS_TCTI just as Javier Martinez Canillas showed on GitHub [4]:
> > 
> > export TPM2TOOLS_TCTI="device:/dev/tpm0"
> > # --auth-policy-session implies --extend-policy-session
> > tpm2_createpolicy --policy-pcr --set-list=sha256:0 \
> > 	--policy-digest-alg=sha256 --auth-policy-session
> > keyctl add trusted test2 \
> > 	"load $(cat /tmp/blob.hex) keyhandle=0x81010001 policyhandle=0x03000000" @u
> > 
> 
> You have the policy handle hardcoded to 0x03000000 here, I guess that's correct
> and is the value printed by tpm2_createpolicy in EXTENDED_POLICY_SESSION_HANDLE?

Yes.

> Sorry for saying the obvious, but just in case since I don't see anything wrong
> with your commands.

No worries. Thanks for your help!

-- 
Thibaut Sautereau
CLIP OS developer