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

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

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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:

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

This last command causes: "add_key: Operation not permitted".
In kernel logs, I have:
	[ 1350.287556] tpm tpm0: A TPM error (2466) occurred unsealing
	[ 1350.289856] trusted_key: key_unseal failed (-1)

The TPM error is 0x9a2, i.e. TPM2_RC_BAD_AUTH. I cannot see what I'm
doing wrong. Do you see something obvious?

[1] https://lkml.org/lkml/2015/11/17/520
[2] https://lkml.org/lkml/2015/11/21/125
[3] https://github.com/jsakkine-intel/tpm2-scripts
[4] https://github.com/tpm2-software/tpm2-tools/issues/510#issuecomment-331385565

Thanks a lot for your time and your work!

-- 
Thibaut Sautereau
CLIP OS developper