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3 Commits
Author SHA1 Message Date
Patrick Colp fba3a474e0 tpm2_key_protector: Implement NV index 
Currently with the TPM2 protector, only SRK mode is supported and
NV index support is just a stub. Implement the NV index option.

Note: This only extends support on the unseal path. grub-protect
has not been updated. tpm2-tools can be used to insert a key into
the NV index.

An example of inserting a key using tpm2-tools:

  # Get random key.
  tpm2_getrandom 32 > key.dat

  # Create primary object.
  tpm2_createprimary -C o -g sha256 -G ecc -c primary.ctx

  # Create policy object. `pcrs.dat` contains the PCR values to seal against.
  tpm2_startauthsession -S session.dat
  tpm2_policypcr -S session.dat -l sha256:7,11 -f pcrs.dat -L policy.dat
  tpm2_flushcontext session.dat

  # Seal key into TPM.
  cat key.dat | tpm2_create -C primary.ctx -u key.pub -r key.priv -L policy.dat -i-
  tpm2_load -C primary.ctx -u key.pub -r key.priv -n sealing.name -c sealing.ctx
  tpm2_evictcontrol -C o -c sealing.ctx 0x81000000

Then to unseal the key in GRUB, add this to grub.cfg:

  tpm2_key_protector_init --mode=nv --nvindex=0x81000000 --pcrs=7,11
  cryptomount -u <UUID> --protector tpm2

Signed-off-by: Patrick Colp <patrick.colp@oracle.com>
Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
 2024-11-28 21:50:55 +01:00
Gary Lin 550ada7d67 tpm2_key_protector: Support authorized policy 
This commit handles the TPM2_PolicyAuthorize command from the key file
in TPM 2.0 Key File format.

TPM2_PolicyAuthorize is the essential command to support authorized
policy which allows the users to sign TPM policies with their own keys.
Per TPM 2.0 Key File [1], CommandPolicy for TPM2_PolicyAuthorize
comprises "TPM2B_PUBLIC pubkey", "TPM2B_DIGEST policy_ref", and
"TPMT_SIGNATURE signature". To verify the signature, the current policy
digest is hashed with the hash algorithm written in "signature", and then
"signature" is verified with the hashed policy digest and "pubkey". Once
TPM accepts "signature", TPM2_PolicyAuthorize is invoked to authorize the
signed policy.

To create the key file with authorized policy, here are the pcr-oracle [2]
commands:

  # Generate the RSA key and create the authorized policy file
  $ pcr-oracle \
	--rsa-generate-key \
	--private-key policy-key.pem \
	--auth authorized.policy \
	create-authorized-policy 0,2,4,7,9

  # Seal the secret with the authorized policy
  $ pcr-oracle \
	--key-format tpm2.0 \
	--auth authorized.policy \
	--input disk-secret.txt \
	--output sealed.key \
	seal-secret

  # Sign the predicted PCR policy
  $ pcr-oracle \
	--key-format tpm2.0 \
	--private-key policy-key.pem \
	--from eventlog \
	--stop-event "grub-file=grub.cfg" \
	--after \
	--input sealed.key \
	--output /boot/efi/efi/grub/sealed.tpm \
	sign 0,2,4,7,9

Then specify the key file and the key protector to grub.cfg in the EFI
system partition:

  tpm2_key_protector_init -a RSA --tpm2key=(hd0,gpt1)/efi/grub/sealed.tpm
  cryptomount -u <PART_UUID> -P tpm2

For any change in the boot components, just run the "sign" command again
to update the signature in sealed.tpm, and TPM can unseal the key file
with the updated PCR policy.

[1] https://www.hansenpartnership.com/draft-bottomley-tpm2-keys.html
[2] https://github.com/okirch/pcr-oracle

Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
 2024-11-28 21:50:55 +01:00
Hernan Gatta 48e230c317 key_protector: Add TPM2 Key Protector 
The TPM2 key protector is a module that enables the automatic retrieval
of a fully-encrypted disk's unlocking key from a TPM 2.0.

The theory of operation is such that the module accepts various
arguments, most of which are optional and therefore possess reasonable
defaults. One of these arguments is the keyfile/tpm2key parameter, which
is mandatory. There are two supported key formats:

1. Raw Sealed Key (--keyfile)
   When sealing a key with TPM2_Create, the public portion of the sealed
   key is stored in TPM2B_PUBLIC, and the private portion is in
   TPM2B_PRIVATE. The raw sealed key glues the fully marshalled
   TPM2B_PUBLIC and TPM2B_PRIVATE into one file.

2. TPM 2.0 Key (--tpm2key)
   The following is the ASN.1 definition of TPM 2.0 Key File:

   TPMPolicy ::= SEQUENCE {
     CommandCode   [0] EXPLICIT INTEGER
     CommandPolicy [1] EXPLICIT OCTET STRING
   }

   TPMAuthPolicy ::= SEQUENCE {
     Name    [0] EXPLICIT UTF8STRING OPTIONAL
     Policy  [1] EXPLICIT SEQUENCE OF TPMPolicy
   }

   TPMKey ::= SEQUENCE {
     type        OBJECT IDENTIFIER
     emptyAuth   [0] EXPLICIT BOOLEAN OPTIONAL
     policy      [1] EXPLICIT SEQUENCE OF TPMPolicy OPTIONAL
     secret      [2] EXPLICIT OCTET STRING OPTIONAL
     authPolicy  [3] EXPLICIT SEQUENCE OF TPMAuthPolicy OPTIONAL
     description [4] EXPLICIT UTF8String OPTIONAL,
     rsaParent   [5] EXPLICIT BOOLEAN OPTIONAL,
     parent      INTEGER
     pubkey      OCTET STRING
     privkey     OCTET STRING
   }

  The TPM2 key protector only expects a "sealed" key in DER encoding,
  so "type" is always 2.23.133.10.1.5, "emptyAuth" is "TRUE", and
  "secret" is empty. "policy" and "authPolicy" are the possible policy
  command sequences to construct the policy digest to unseal the key.
  Similar to the raw sealed key, the public portion (TPM2B_PUBLIC) of
  the sealed key is stored in "pubkey", and the private portion
  (TPM2B_PRIVATE) is in "privkey".

  For more details: https://www.hansenpartnership.com/draft-bottomley-tpm2-keys.html

This sealed key file is created via the grub-protect tool. The tool
utilizes the TPM's sealing functionality to seal (i.e., encrypt) an
unlocking key using a Storage Root Key (SRK) to the values of various
Platform Configuration Registers (PCRs). These PCRs reflect the state
of the system as it boots. If the values are as expected, the system
may be considered trustworthy, at which point the TPM allows for a
caller to utilize the private component of the SRK to unseal (i.e.,
decrypt) the sealed key file. The caller, in this case, is this key
protector.

The TPM2 key protector registers two commands:

  - tpm2_key_protector_init: Initializes the state of the TPM2 key
                             protector for later usage, clearing any
                             previous state, too, if any.

  - tpm2_key_protector_clear: Clears any state set by tpm2_key_protector_init.

The way this is expected to be used requires the user to, either
interactively or, normally, via a boot script, initialize/configure
the key protector and then specify that it be used by the "cryptomount"
command (modifications to this command are in a different patch).

For instance, to unseal the raw sealed key file:

  tpm2_key_protector_init --keyfile=(hd0,gpt1)/efi/grub/sealed-1.key
  cryptomount -u <PART1_UUID> -P tpm2

  tpm2_key_protector_init --keyfile=(hd0,gpt1)/efi/grub/sealed-2.key --pcrs=7,11
  cryptomount -u <PART2_UUID> -P tpm2

Or, to unseal the TPM 2.0 Key file:

  tpm2_key_protector_init --tpm2key=(hd0,gpt1)/efi/grub/sealed-1.tpm
  cryptomount -u <PART1_UUID> -P tpm2

  tpm2_key_protector_init --tpm2key=(hd0,gpt1)/efi/grub/sealed-2.tpm --pcrs=7,11
  cryptomount -u <PART2_UUID> -P tpm2

If a user does not initialize the key protector and attempts to use it
anyway, the protector returns an error.

Before unsealing the key, the TPM2 key protector follows the "TPMPolicy"
sequences to enforce the TPM policy commands to construct a valid policy
digest to unseal the key.

For the TPM 2.0 Key files, "authPolicy" may contain multiple "TPMPolicy"
sequences, the TPM2 key protector iterates "authPolicy" to find a valid
sequence to unseal key. If "authPolicy" is empty or all sequences in
"authPolicy" fail, the protector tries the one from "policy". In case
"policy" is also empty, the protector creates a "TPMPolicy" sequence
based on the given PCR selection.

For the raw sealed key, the TPM2 key protector treats the key file as a
TPM 2.0 Key file without "authPolicy" and "policy", so the "TPMPolicy"
sequence is always based on the PCR selection from the command
parameters.

This commit only supports one policy command: TPM2_PolicyPCR. The
command set will be extended to support advanced features, such as
authorized policy, in the later commits.

Cc: James Bottomley <jejb@linux.ibm.com>
Signed-off-by: Hernan Gatta <hegatta@linux.microsoft.com>
Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
 2024-11-28 21:50:55 +01:00