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 <hega...@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 <stef...@linux.ibm.com>
> > Cc: James Bottomley <j...@linux.ibm.com>
> > Signed-off-by: Hernan Gatta <hega...@linux.microsoft.com>
> > Signed-off-by: Gary Lin <g...@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
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