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From: Patrick Uiterwijk <>
	Patrick Uiterwijk <>
Subject: [PATCH 0/3] Load keys from TPM2 NV Index on IMA keyring
Date: Thu, 25 Feb 2021 21:32:26 +0100	[thread overview]
Message-ID: <> (raw)

The system's signature chain of trust is rooted in hardware and pivots to
the keys baked into the kernel. IMA maintains this signature chain of trust
by requiring any key being added to the IMA trusted keyring to be signed by
a key on the builtin (or secondary) keyrings. This prevents a local key,
needed for signing policies or other files, from being loaded on the IMA
keyring, without requiring a custom built kernel (or injecting a key and
resigning the kernel image).

Allow users to load their own public key stored in a specific TPM2 NV
Index, requiring the absence of the Platform Create and Platform Write
attributes on the NV Index, to be loaded on the IMA keyring.

To test this with the TPM2-software tools with a DER-encoded imacert.der:
  tpm2_nvdefine -C o -s 945 0x184b520
  tpm2_nvwrite -C o -i imacert.der 0x184b520

Or with the IBM TSS tools:
  tssnvdefinespace -ha 0x184b520 -hi o -sz 945 +at ow +at or
  tssnvwrite -hia o -ha 0x184b520 -if imacert.der

Then after a reboot, the ima keyring should contain the certificate.

Note that if this feature is enabled, users should make sure an NV Index
is created with accurate attributes to prevent any other users from
writing or deleting the NV Index. Without this precaution, any user who
has access to the TPM would be able to write a key to the NV Index and have
that key loaded on the IMA trusted keyring.

A distro who wants to enable this feature, for example, should ensure that
the installer defines the NV Index in all cases, and only fills it if a key
was provided by the user.

It is strongly adviced that any NV Index created for this purpose has at
least the policy_delete and policywrite attributes set, together with a
non-empty policy. Those flags make sure that the policy (which would be up
to them to define) is required to be satisfied to delete or write the index.

Patrick Uiterwijk (3):
  tpm: Add support for reading a TPM NV Index
  integrity: Allow specifying flags in integrity_load_cert
  integrity: Load keys from TPM NV onto IMA keyring

 drivers/char/tpm/tpm-interface.c              |  30 ++++
 drivers/char/tpm/tpm.h                        |   5 +
 drivers/char/tpm/tpm2-cmd.c                   | 163 ++++++++++++++++++
 include/linux/tpm.h                           |  65 +++++++
 security/integrity/digsig.c                   |  11 +-
 security/integrity/ima/Kconfig                |  22 +++
 security/integrity/ima/ima_init.c             |  53 ++++++
 security/integrity/integrity.h                |   6 +-
 .../platform_certs/platform_keyring.c         |   2 +-
 9 files changed, 349 insertions(+), 8 deletions(-)


             reply	other threads:[~2021-02-25 20:36 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-25 20:32 Patrick Uiterwijk [this message]
2021-02-25 20:32 ` [PATCH 1/3] tpm: Add support for reading a TPM NV Index Patrick Uiterwijk
2021-02-25 21:50   ` Stefan Berger
2021-02-26  1:09   ` Jarkko Sakkinen
2021-02-25 20:32 ` [PATCH 2/3] integrity: Allow specifying flags in integrity_load_cert Patrick Uiterwijk
2021-02-26 21:04   ` Stefan Berger
2021-02-25 20:32 ` [PATCH 3/3] integrity: Load keys from TPM NV onto IMA keyring Patrick Uiterwijk
2021-02-26 21:47   ` Stefan Berger
2021-02-26 21:51     ` Stefan Berger
2021-02-25 21:50 ` [PATCH 0/3] Load keys from TPM2 NV Index on " James Bottomley
2021-02-26 21:45   ` Ken Goldman

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