Re: [PATCH v18 16/25] key_protector: Add TPM2 Key Protector

[Gary Lin]

On Mon, Aug 26, 2024 at 04:32:16PM +0200, Daniel Kiper wrote:
> On Fri, Jun 28, 2024 at 04:18:59PM +0800, Gary Lin via Grub-devel wrote:
> > From: Hernan Gatta <hegatta@linux.microsoft.com>
> >
> > 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 construst 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/grub2/sealed-1.key
> > cryptomount -u <PART1_UUID> -P tpm2
> >
> > tpm2_key_protector_init --keyfile=(hd0,gpt1)/efi/grub2/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/grub2/sealed-1.tpm
> > cryptomount -u <PART1_UUID> -P tpm2
> >
> > tpm2_key_protector_init --tpm2key=(hd0,gpt1)/efi/grub2/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: Stefan Berger <stefanb@linux.ibm.com>
> > Cc: James Bottomley <jejb@linux.ibm.com>
> > Signed-off-by: Hernan Gatta <hegatta@linux.microsoft.com>
> > Signed-off-by: Gary Lin <glin@suse.com>
> > ---
> >  grub-core/Makefile.core.def                   |   11 +
> >  grub-core/commands/tpm2_key_protector/args.c  |  130 ++
> >  .../commands/tpm2_key_protector/module.c      | 1162 +++++++++++++++++
> >  grub-core/commands/tpm2_key_protector/tpm2.h  |   36 +
> >  .../commands/tpm2_key_protector/tpm2_args.h   |   51 +
> >  .../commands/tpm2_key_protector/tpm2key.asn   |   49 +
> >  .../commands/tpm2_key_protector/tpm2key.c     |  499 +++++++
> >  .../commands/tpm2_key_protector/tpm2key.h     |   87 ++
> >  .../tpm2_key_protector/tpm2key_asn1_tab.c     |   63 +
> >  9 files changed, 2088 insertions(+)
> >  create mode 100644 grub-core/commands/tpm2_key_protector/args.c
> >  create mode 100644 grub-core/commands/tpm2_key_protector/module.c
> >  create mode 100644 grub-core/commands/tpm2_key_protector/tpm2.h
> >  create mode 100644 grub-core/commands/tpm2_key_protector/tpm2_args.h
> >  create mode 100644 grub-core/commands/tpm2_key_protector/tpm2key.asn
> >  create mode 100644 grub-core/commands/tpm2_key_protector/tpm2key.c
> >  create mode 100644 grub-core/commands/tpm2_key_protector/tpm2key.h
> >  create mode 100644 grub-core/commands/tpm2_key_protector/tpm2key_asn1_tab.c
> >
> 
> [...]
> 
> > diff --git a/grub-core/commands/tpm2_key_protector/module.c 
> > b/grub-core/commands/tpm2_key_protector/module.c
> > new file mode 100644
> > index 000000000..79440474b
> > --- /dev/null
> > +++ b/grub-core/commands/tpm2_key_protector/module.c
> 
> [...]
> 
> > +static grub_err_t
> > +grub_tpm2_protector_srk_read_file (const char *filepath, void **buffer,
> > +                              grub_size_t *buffer_size)
> > +{
> > +  grub_file_t file;
> > +  grub_off_t file_size;
> > +  void *read_buffer;
> > +  grub_off_t read_n;
> > +  grub_err_t err;
> > +
> > +  /* Using GRUB_FILE_TYPE_SIGNATURE ensures we do not hash the keyfile 
> > into PCR9
> > +   * otherwise we'll never be able to predict the value of PCR9 at unseal 
> > time */
> 
> Wrong coding style...
> 
Will fix it in the next version.

> > +  file = grub_file_open (filepath, GRUB_FILE_TYPE_SIGNATURE);
> > +  if (file == NULL)
> > +    {
> > +      /* Push errno from grub_file_open() into the error message stack */
> > +      grub_error_push();
> > +      err = grub_error (GRUB_ERR_FILE_NOT_FOUND, N_("Could not open file: 
> > %s\n"), filepath);
> > +      goto error;
> > +    }
> > +
> > +  file_size = grub_file_size (file);
> > +  if (file_size == 0)
> > +    {
> > +      err = grub_error (GRUB_ERR_OUT_OF_RANGE, N_("Could not read file 
> > size: %s"), filepath);
> > +      goto error;
> > +    }
> > +
> > +  read_buffer = grub_malloc (file_size);
> > +  if (read_buffer == NULL)
> > +    {
> > +      err = grub_error (GRUB_ERR_OUT_OF_MEMORY, N_("Could not allocate 
> > buffer for %s"), filepath);
> > +      goto error;
> > +    }
> > +
> > +  read_n = grub_file_read (file, read_buffer, file_size);
> > +  if (read_n != file_size)
> > +    {
> > +      grub_free (read_buffer);
> > +      err = grub_error (GRUB_ERR_FILE_READ_ERROR, N_("Could not retrieve 
> > file contents: %s"), filepath);
> > +      goto error;
> > +    }
> > +
> > +  *buffer = read_buffer;
> > +  *buffer_size = file_size;
> > +
> > +  err = GRUB_ERR_NONE;
> > +
> > + error:
> > +  if (file != NULL)
> > +    grub_file_close (file);
> > +
> > +  return err;
> > +}
> > +
> > +static grub_err_t
> > +grub_tpm2_protector_srk_unmarshal_keyfile (void *sealed_key,
> > +                                      grub_size_t sealed_key_size,
> > +                                      tpm2_sealed_key_t *sk)
> > +{
> > +  struct grub_tpm2_buffer buf;
> > +
> > +  grub_tpm2_buffer_init (&buf);
> > +  if (sealed_key_size > buf.cap)
> > +    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("Sealed key larger than 
> > %" PRIuGRUB_SIZE " bytes"), buf.cap);
> 
> Macros, e.g PRIuGRUB_SIZE, cannot be used in _() and N_() macros.
> 
> In general please double check _() and N_() macros usage and drop some
> of them as Vladimir suggested.
> 
Sure, I've removed all _() and N_() from all grub_error() in my working
branch.

> [...]
> 
> > diff --git a/grub-core/commands/tpm2_key_protector/tpm2key_asn1_tab.c 
> > b/grub-core/commands/tpm2_key_protector/tpm2key_asn1_tab.c
> > new file mode 100644
> > index 000000000..bebe108a3
> > --- /dev/null
> > +++ b/grub-core/commands/tpm2_key_protector/tpm2key_asn1_tab.c
> > @@ -0,0 +1,63 @@
> > +/*
> > + *  GRUB  --  GRand Unified Bootloader
> > + *  Copyright (C) 2024 Free Software Foundation, Inc.
> > + *
> > + *  GRUB is free software: you can redistribute it and/or modify
> > + *  it under the terms of the GNU General Public License as published by
> > + *  the Free Software Foundation, either version 3 of the License, or
> > + *  (at your option) any later version.
> > + *
> > + *  GRUB is distributed in the hope that it will be useful,
> > + *  but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + *  GNU General Public License for more details.
> > + *
> > + *  You should have received a copy of the GNU General Public License
> > + *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
> > + */
> > +
> > +/*
> > + *  This file is generated by 'asn1Parser tpm2key.asn' and the '#include'
> > + *  headers are replaced with the ones in grub2.
> > + *  - 'grub/mm.h' for the definition of 'NULL'
> > + *  - 'libtasn1.h' for the definition of 'asn1_static_node'
> 
> I think the configure.ac should be updated to check for availability of
> asn1Parser command. This requirement should be reflected in INSTALL file
> too.
> 
I manually ran the asn1Parser command to generate the C file and then
edited the file to add the copyright header and replace the header
files. Should I generate the C file at build time?

Gary Lin