[PATCH v2 3/5] protectors: Add TPM2 Key Protector

[Hernan Gatta]

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 parameter, which is mandatory.

The value of this parameter must be a path to a sealed key file (e.g.,
(hd0,gpt1)/boot/grub2/sealed_key). 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 (i.e., 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:

tpm2_key_protector_init --keyfile=KEYFILE1
cryptomount DISK1 -k tpm2

tpm2_key_protector_init --keyfile=KEYFILE2 --pcrs=7,11
cryptomount DISK2 -k tpm2

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

Signed-off-by: Hernan Gatta <hegatta@linux.microsoft.com>
---
 grub-core/Makefile.core.def       |  10 +
 grub-core/tpm2/args.c             | 129 +++++++
 grub-core/tpm2/module.c           | 710 ++++++++++++++++++++++++++++++++++++++
 include/grub/tpm2/internal/args.h |  39 +++
 4 files changed, 888 insertions(+)
 create mode 100644 grub-core/tpm2/args.c
 create mode 100644 grub-core/tpm2/module.c
 create mode 100644 include/grub/tpm2/internal/args.h

diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index e4ae78b..78d09d9 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -2498,6 +2498,16 @@ module = {
 };
 
 module = {
+  name = tpm2;
+  common = tpm2/args.c;
+  common = tpm2/buffer.c;
+  common = tpm2/module.c;
+  common = tpm2/mu.c;
+  common = tpm2/tpm2.c;
+  efi = tpm2/tcg2.c;
+};
+
+module = {
   name = tr;
   common = commands/tr.c;
 };
diff --git a/grub-core/tpm2/args.c b/grub-core/tpm2/args.c
new file mode 100644
index 0000000..90c7cd8
--- /dev/null
+++ b/grub-core/tpm2/args.c
@@ -0,0 +1,129 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2022 Microsoft Corporation
+ *
+ *  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/>.
+ */
+
+#include <grub/err.h>
+#include <grub/mm.h>
+#include <grub/misc.h>
+#include <grub/tpm2/internal/args.h>
+
+grub_err_t
+grub_tpm2_protector_parse_pcrs (char *value, grub_uint8_t *pcrs,
+                                grub_uint8_t *pcr_count)
+{
+  char *current_pcr = value;
+  char *next_pcr;
+  unsigned long pcr;
+  grub_uint8_t i;
+
+  if (grub_strlen (value) == 0)
+    return GRUB_ERR_BAD_ARGUMENT;
+
+  *pcr_count = 0;
+  for (i = 0; i < TPM_MAX_PCRS; i++)
+    {
+      next_pcr = grub_strchr (current_pcr, ',');
+      if (next_pcr == current_pcr)
+        return grub_error (GRUB_ERR_BAD_ARGUMENT,
+                           N_("Empty entry in PCR list"));
+      if (next_pcr)
+        *next_pcr = '\0';
+
+      grub_errno = GRUB_ERR_NONE;
+      pcr = grub_strtoul (current_pcr, NULL, 10);
+      if (grub_errno != GRUB_ERR_NONE)
+        return grub_error (grub_errno,
+                           N_("Entry '%s' in PCR list is not a number"),
+                           current_pcr);
+
+      if (pcr > TPM_MAX_PCRS)
+        return grub_error (GRUB_ERR_OUT_OF_RANGE,
+                           N_("Entry %lu in PCR list is too large to be a PCR "
+                              "number, PCR numbers range from 0 to %u"),
+                           pcr, TPM_MAX_PCRS);
+
+      pcrs[i] = (grub_uint8_t)pcr;
+      *pcr_count += 1;
+
+      if (!next_pcr)
+        break;
+
+      current_pcr = next_pcr + 1;
+      if (*current_pcr == '\0')
+        return grub_error (GRUB_ERR_BAD_ARGUMENT,
+                           N_("Trailing comma at the end of PCR list"));
+    }
+
+  if (i == TPM_MAX_PCRS)
+    return grub_error (GRUB_ERR_OUT_OF_RANGE,
+                       N_("Too many PCRs in PCR list, the maximum number of "
+                          "PCRs is %u"), TPM_MAX_PCRS);
+
+  return GRUB_ERR_NONE;
+}
+
+grub_err_t
+grub_tpm2_protector_parse_asymmetric (const char *value, TPM_ALG_ID 
*asymmetric)
+{
+  if (grub_strcasecmp (value, "ECC") == 0)
+    *asymmetric = TPM_ALG_ECC;
+  else if (grub_strcasecmp (value, "RSA") == 0)
+    *asymmetric = TPM_ALG_RSA;
+  else
+    return grub_error (GRUB_ERR_OUT_OF_RANGE,
+                       N_("Value '%s' is not a valid asymmetric key type"),
+                       value);
+
+  return GRUB_ERR_NONE;
+}
+
+grub_err_t
+grub_tpm2_protector_parse_bank (const char *value, TPM_ALG_ID *bank)
+{
+  if (grub_strcasecmp (value, "SHA1") == 0)
+    *bank = TPM_ALG_SHA1;
+  else if (grub_strcasecmp (value, "SHA256") == 0)
+    *bank = TPM_ALG_SHA256;
+  else if (grub_strcasecmp (value, "SHA384") == 0)
+    *bank = TPM_ALG_SHA384;
+  else
+    return grub_error (GRUB_ERR_OUT_OF_RANGE,
+                       N_("Value '%s' is not a valid PCR bank"), value);
+
+  return GRUB_ERR_NONE;
+}
+
+grub_err_t
+grub_tpm2_protector_parse_tpm_handle (const char *value, TPM_HANDLE *handle)
+{
+  unsigned long num;
+
+  grub_errno = GRUB_ERR_NONE;
+  num = grub_strtoul (value, NULL, 0);
+  if (grub_errno != GRUB_ERR_NONE)
+    return grub_error (grub_errno, N_("TPM handle value '%s' is not a number"),
+                       value);
+
+  if (num > GRUB_UINT_MAX)
+    return grub_error (GRUB_ERR_OUT_OF_RANGE,
+                       N_("Value %lu is too large to be a TPM handle, TPM "
+                          "handles are unsigned 32-bit integers"), num);
+
+  *handle = (TPM_HANDLE)num;
+
+  return GRUB_ERR_NONE;
+}
diff --git a/grub-core/tpm2/module.c b/grub-core/tpm2/module.c
new file mode 100644
index 0000000..3f2f386
--- /dev/null
+++ b/grub-core/tpm2/module.c
@@ -0,0 +1,710 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2022 Microsoft Corporation
+ *
+ *  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/>.
+ */
+
+#include <grub/dl.h>
+#include <grub/extcmd.h>
+#include <grub/file.h>
+#include <grub/misc.h>
+#include <grub/mm.h>
+#include <grub/protector.h>
+#include <grub/tpm2/buffer.h>
+#include <grub/tpm2/internal/args.h>
+#include <grub/tpm2/mu.h>
+#include <grub/tpm2/tpm2.h>
+
+GRUB_MOD_LICENSE ("GPLv3+");
+
+typedef enum grub_tpm2_protector_mode
+{
+  GRUB_TPM2_PROTECTOR_MODE_UNSET,
+  GRUB_TPM2_PROTECTOR_MODE_SRK,
+  GRUB_TPM2_PROTECTOR_MODE_NV
+} grub_tpm2_protector_mode_t;
+
+struct grub_tpm2_protector_context
+{
+  grub_tpm2_protector_mode_t mode;
+  grub_uint8_t pcrs[TPM_MAX_PCRS];
+  grub_uint8_t pcr_count;
+  TPM_ALG_ID asymmetric;
+  TPM_ALG_ID bank;
+  const char *keyfile;
+  TPM_HANDLE srk;
+  TPM_HANDLE nv;
+};
+
+static const struct grub_arg_option grub_tpm2_protector_init_cmd_options[] =
+  {
+    /* Options for all modes */
+    {
+      .longarg  = "mode",
+      .shortarg = 'm',
+      .flags    = 0,
+      .arg      = NULL,
+      .type     = ARG_TYPE_STRING,
+      .doc      =
+        N_("Unseal key using SRK ('srk') (default) or retrieve it from an NV "
+           "Index ('nv')."),
+    },
+    {
+      .longarg  = "pcrs",
+      .shortarg = 'p',
+      .flags    = 0,
+      .arg      = NULL,
+      .type     = ARG_TYPE_STRING,
+      .doc      =
+        N_("Comma-separated list of PCRs used to authorize key release "
+           "(e.g., '7,11', default is 7."),
+    },
+    {
+      .longarg  = "bank",
+      .shortarg = 'b',
+      .flags    = 0,
+      .arg      = NULL,
+      .type     = ARG_TYPE_STRING,
+      .doc      =
+        N_("Bank of PCRs used to authorize key release: "
+           "SHA1, SHA256 (default), or SHA384."),
+    },
+    /* SRK-mode options */
+    {
+      .longarg  = "keyfile",
+      .shortarg = 'k',
+      .flags    = 0,
+      .arg      = NULL,
+      .type     = ARG_TYPE_STRING,
+      .doc      =
+        N_("Required in SRK mode, path to the sealed key file to unseal using "
+           "the TPM (e.g., (hd0,gpt1)/boot/grub2/sealed_key)."),
+    },
+    {
+      .longarg  = "srk",
+      .shortarg = 's',
+      .flags    = 0,
+      .arg      = NULL,
+      .type     = ARG_TYPE_STRING,
+      .doc      =
+        N_("In SRK mode, the SRK handle if the SRK is persistent "
+           "(default is 0x81000001)."),
+    },
+    {
+      .longarg  = "asymmetric",
+      .shortarg = 'a',
+      .flags    = 0,
+      .arg      = NULL,
+      .type     = ARG_TYPE_STRING,
+      .doc      =
+        N_("In SRK mode, the type of SRK: RSA (default) or ECC."),
+    },
+    /* NV Index-mode options */
+    {
+      .longarg  = "nvindex",
+      .shortarg = 'n',
+      .flags    = 0,
+      .arg      = NULL,
+      .type     = ARG_TYPE_STRING,
+      .doc      =
+        N_("Required in NV Index mode, the NV handle to read which must "
+           "readily exist on the TPM and which contains the key."),
+    },
+    /* End of list */
+    {0, 0, 0, 0, 0, 0}
+  };
+
+static grub_extcmd_t grub_tpm2_protector_init_cmd;
+static grub_extcmd_t grub_tpm2_protector_clear_cmd;
+static struct grub_tpm2_protector_context grub_tpm2_protector_ctx = { 0 };
+
+static grub_err_t
+grub_tpm2_protector_srk_read_keyfile (const char *filepath, void **buffer,
+                                      grub_size_t *buffer_size)
+{
+  grub_file_t sealed_key_file;
+  grub_off_t sealed_key_size;
+  void *sealed_key_buffer;
+  grub_off_t sealed_key_read;
+
+  sealed_key_file = grub_file_open (filepath, GRUB_FILE_TYPE_NONE);
+  if (!sealed_key_file)
+    {
+      grub_dprintf ("tpm2", "Could not open sealed key file.\n");
+      /* grub_file_open sets grub_errno on error, and if we do no unset it,
+       * future calls to grub_file_open will fail (and so will anybody up the
+       * stack who checks the value, if any). */
+      grub_errno = GRUB_ERR_NONE;
+      return GRUB_ERR_FILE_NOT_FOUND;
+    }
+
+  sealed_key_size = grub_file_size (sealed_key_file);
+  if (!sealed_key_size)
+    {
+      grub_dprintf ("tpm2", "Could not read sealed key file size.\n");
+      grub_file_close (sealed_key_file);
+      return GRUB_ERR_OUT_OF_RANGE;
+    }
+
+  sealed_key_buffer = grub_malloc (sealed_key_size);
+  if (!sealed_key_buffer)
+    {
+      grub_dprintf ("tpm2", "Could not allocate buffer for sealed key.\n");
+      grub_file_close (sealed_key_file);
+      return GRUB_ERR_OUT_OF_MEMORY;
+    }
+
+  sealed_key_read = grub_file_read (sealed_key_file, sealed_key_buffer,
+                                    sealed_key_size);
+  if (sealed_key_read != sealed_key_size)
+    {
+      grub_dprintf ("tpm2", "Could not retrieve sealed key file contents.\n");
+      grub_free (sealed_key_buffer);
+      grub_file_close (sealed_key_file);
+      return GRUB_ERR_FILE_READ_ERROR;
+    }
+
+  grub_file_close (sealed_key_file);
+
+  *buffer = sealed_key_buffer;
+  *buffer_size = sealed_key_size;
+
+  return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+grub_tpm2_protector_srk_unmarshal_keyfile (void *sealed_key,
+                                           grub_size_t sealed_key_size,
+                                           TPM2_SEALED_KEY *sk)
+{
+  struct grub_tpm2_buffer buf;
+
+  grub_tpm2_buffer_init (&buf);
+  if (sealed_key_size > buf.cap)
+    {
+      grub_dprintf ("tpm2", "Sealed key file is larger than decode buffer "
+                            "(%lu vs %lu bytes).\n", sealed_key_size, buf.cap);
+      return GRUB_ERR_BAD_ARGUMENT;
+    }
+
+  grub_memcpy (buf.data, sealed_key, sealed_key_size);
+  buf.size = sealed_key_size;
+
+  grub_tpm2_mu_TPM2B_PUBLIC_Unmarshal (&buf, &sk->public);
+  grub_tpm2_mu_TPM2B_Unmarshal (&buf, (TPM2B *)&sk->private);
+
+  if (buf.error)
+    {
+      grub_dprintf ("tpm2", "Could not unmarshal sealed key file, it is likely 
"
+                            "malformed.\n");
+      return GRUB_ERR_BAD_ARGUMENT;
+    }
+
+  return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+grub_tpm2_protector_srk_get (const struct grub_tpm2_protector_context *ctx,
+                             TPM_HANDLE *srk)
+{
+  TPM_RC rc;
+  TPM2B_PUBLIC public;
+  TPMS_AUTH_COMMAND authCommand = { 0 };
+  TPM2B_SENSITIVE_CREATE inSensitive = { 0 };
+  TPM2B_PUBLIC inPublic = { 0 };
+  TPM2B_DATA outsideInfo = { 0 };
+  TPML_PCR_SELECTION creationPcr = { 0 };
+  TPM2B_PUBLIC outPublic = { 0 };
+  TPM2B_CREATION_DATA creationData = { 0 };
+  TPM2B_DIGEST creationHash = { 0 };
+  TPMT_TK_CREATION creationTicket = { 0 };
+  TPM2B_NAME srkName = { 0 };
+  TPM_HANDLE srkHandle;
+
+  /* Find SRK */
+  rc = TPM2_ReadPublic (ctx->srk, NULL, &public);
+  if (rc == TPM_RC_SUCCESS)
+    {
+      *srk = ctx->srk;
+      return GRUB_ERR_NONE;
+    }
+
+  /* The handle exists but its public area could not be read. */
+  if ((rc & ~TPM_RC_N_MASK) != TPM_RC_HANDLE)
+    {
+      grub_dprintf ("tpm2", "The SRK handle (0x%x) exists on the TPM but its "
+                            "public area could not be read (TPM2_ReadPublic "
+                            "failed with TSS/TPM error %u).\n", ctx->srk, rc);
+      return GRUB_ERR_BAD_DEVICE;
+    }
+
+  /* Create SRK */
+  authCommand.sessionHandle = TPM_RS_PW;
+  inPublic.publicArea.type = ctx->asymmetric;
+  inPublic.publicArea.nameAlg  = TPM_ALG_SHA256;
+  inPublic.publicArea.objectAttributes.restricted = 1;
+  inPublic.publicArea.objectAttributes.userWithAuth = 1;
+  inPublic.publicArea.objectAttributes.decrypt = 1;
+  inPublic.publicArea.objectAttributes.fixedTPM = 1;
+  inPublic.publicArea.objectAttributes.fixedParent = 1;
+  inPublic.publicArea.objectAttributes.sensitiveDataOrigin = 1;
+  inPublic.publicArea.objectAttributes.noDA = 1;
+
+  if (ctx->asymmetric == TPM_ALG_RSA)
+    {
+      inPublic.publicArea.parameters.rsaDetail.symmetric.algorithm = 
TPM_ALG_AES;
+      inPublic.publicArea.parameters.rsaDetail.symmetric.keyBits.aes = 128;
+      inPublic.publicArea.parameters.rsaDetail.symmetric.mode.aes = 
TPM_ALG_CFB;
+      inPublic.publicArea.parameters.rsaDetail.scheme.scheme = TPM_ALG_NULL;
+      inPublic.publicArea.parameters.rsaDetail.keyBits = 2048;
+      inPublic.publicArea.parameters.rsaDetail.exponent = 0;
+    }
+  else if (ctx->asymmetric == TPM_ALG_ECC)
+    {
+      inPublic.publicArea.parameters.eccDetail.symmetric.algorithm = 
TPM_ALG_AES;
+      inPublic.publicArea.parameters.eccDetail.symmetric.keyBits.aes = 128;
+      inPublic.publicArea.parameters.eccDetail.symmetric.mode.aes = 
TPM_ALG_CFB;
+      inPublic.publicArea.parameters.eccDetail.scheme.scheme = TPM_ALG_NULL;
+      inPublic.publicArea.parameters.eccDetail.curveID = TPM_ECC_NIST_P256;
+      inPublic.publicArea.parameters.eccDetail.kdf.scheme = TPM_ALG_NULL;
+    }
+  else
+    return GRUB_ERR_BAD_ARGUMENT;
+
+  rc = TPM2_CreatePrimary (TPM_RH_OWNER, &authCommand, &inSensitive, &inPublic,
+                           &outsideInfo, &creationPcr, &srkHandle, &outPublic,
+                           &creationData, &creationHash, &creationTicket,
+                           &srkName, NULL);
+  if (rc != TPM_RC_SUCCESS)
+    {
+      grub_dprintf ("tpm2", "Could not create SRK (TPM2_CreatePrimary failed "
+                            "with TSS/TPM error %u).\n", rc);
+      return GRUB_ERR_BAD_DEVICE;
+    }
+
+  *srk = srkHandle;
+
+  return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+grub_tpm2_protector_srk_recover (const struct grub_tpm2_protector_context *ctx,
+                                 grub_uint8_t **key, grub_size_t *key_size)
+{
+  TPM_RC rc;
+  TPM2_SEALED_KEY sealed_key;
+  void *sealed_key_bytes;
+  grub_size_t sealed_key_size;
+  TPM_HANDLE srk_handle;
+  TPM2B_NONCE nonceCaller = { 0 };
+  TPM2B_ENCRYPTED_SECRET salt = { 0 };
+  TPMT_SYM_DEF symmetric = { 0 };
+  TPM2B_NONCE nonceTPM = { 0 };
+  TPMI_SH_AUTH_SESSION session;
+  TPML_PCR_SELECTION pcrSel = {
+    .count = 1,
+    .pcrSelections = {
+      {
+        .hash = ctx->bank,
+        .sizeOfSelect = 3,
+        .pcrSelect = { 0 }
+      },
+    }
+  };
+  TPMS_AUTH_COMMAND authCmd = { 0 };
+  TPM_HANDLE sealed_key_handle;
+  TPM2B_NAME name;
+  TPMS_AUTH_RESPONSE authResponse;
+  TPM2B_SENSITIVE_DATA data;
+  grub_uint8_t *key_out;
+  grub_uint8_t i;
+  grub_err_t err;
+
+  /* Retrieve Sealed Key */
+  err = grub_tpm2_protector_srk_read_keyfile (ctx->keyfile, &sealed_key_bytes,
+                                              &sealed_key_size);
+  if (err)
+    return grub_error (err, N_("Failed to read key file %s"), ctx->keyfile);
+
+  err = grub_tpm2_protector_srk_unmarshal_keyfile (sealed_key_bytes,
+                                                   sealed_key_size,
+                                                   &sealed_key);
+  if (err)
+    {
+      grub_error (err, N_("Failed to unmarshal key, ensure the key file is in "
+                          "TPM wire format"));
+      goto exit1;
+    }
+
+  /* Get SRK */
+  err = grub_tpm2_protector_srk_get (ctx, &srk_handle);
+  if (err)
+    {
+      grub_error (err, N_("Failed to retrieve the SRK"));
+      goto exit1;
+    }
+
+  err = GRUB_ERR_BAD_DEVICE;
+
+  /* Start Auth Session */
+  nonceCaller.size = TPM_SHA256_DIGEST_SIZE;
+  symmetric.algorithm = TPM_ALG_NULL;
+
+  rc = TPM2_StartAuthSession (TPM_RH_NULL, TPM_RH_NULL, 0, &nonceCaller, &salt,
+                              TPM_SE_POLICY, &symmetric, TPM_ALG_SHA256,
+                              &session, &nonceTPM, 0);
+  if (rc)
+    {
+      grub_error (err, N_("Failed to start auth session (TPM2_StartAuthSession 
"
+                          "failed with TSS/TPM error %u)"), rc);
+      goto exit2;
+    }
+
+  /* Policy PCR */
+  for (i = 0; i < ctx->pcr_count; i++)
+    pcrSel
+      .pcrSelections[0]
+      .pcrSelect[TPM2_PCR_TO_SELECT(ctx->pcrs[i])]
+        |= TPM2_PCR_TO_BIT(ctx->pcrs[i]);
+
+  rc = TPM2_PolicyPCR (session, NULL, NULL, &pcrSel, NULL);
+  if (rc)
+    {
+      grub_error (err, N_("Failed to submit PCR policy (TPM2_PolicyPCR failed "
+                          "with TSS/TPM error %u)"), rc);
+      goto exit3;
+    }
+
+  /* Load Sealed Key */
+  authCmd.sessionHandle = TPM_RS_PW;
+  rc = TPM2_Load (srk_handle, &authCmd, &sealed_key.private, 
&sealed_key.public,
+                  &sealed_key_handle, &name, &authResponse);
+  if (rc)
+    {
+      grub_error (err, N_("Failed to load sealed key (TPM2_Load failed with "
+                          "TSS/TPM error %u)"), rc);
+      goto exit3;
+    }
+
+  /* Unseal Sealed Key */
+  authCmd.sessionHandle = session;
+  grub_memset (&authResponse, 0, sizeof (authResponse));
+
+  rc = TPM2_Unseal (sealed_key_handle, &authCmd, &data, &authResponse);
+  if (rc)
+    {
+      grub_error (err, N_("Failed to unseal sealed key (TPM2_Unseal failed "
+                          "with TSS/TPM error %u)"), rc);
+      goto exit4;
+    }
+
+  /* Epilogue */
+  key_out = grub_malloc (data.size);
+  if (!key_out)
+    {
+      err = GRUB_ERR_OUT_OF_MEMORY;
+      grub_error (err, N_("No memory left to allocate unlock key buffer"));
+      goto exit4;
+    }
+
+  grub_memcpy (key_out, data.buffer, data.size);
+
+  *key = key_out;
+  *key_size = data.size;
+
+  err = GRUB_ERR_NONE;
+
+exit4:
+  TPM2_FlushContext (sealed_key_handle);
+
+exit3:
+  TPM2_FlushContext (session);
+
+exit2:
+  TPM2_FlushContext (srk_handle);
+
+exit1:
+  grub_free (sealed_key_bytes);
+  return err;
+}
+
+static grub_err_t
+grub_tpm2_protector_nv_recover (const struct grub_tpm2_protector_context *ctx,
+                                grub_uint8_t **key, grub_size_t *key_size)
+{
+  (void)ctx;
+  (void)key;
+  (void)key_size;
+
+  return grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
+                     N_("NV Index mode is not implemented yet"));
+}
+
+static grub_err_t
+grub_tpm2_protector_recover (const struct grub_tpm2_protector_context *ctx,
+                             grub_uint8_t **key, grub_size_t *key_size)
+{
+  switch (ctx->mode)
+    {
+    case GRUB_TPM2_PROTECTOR_MODE_SRK:
+      return grub_tpm2_protector_srk_recover (ctx, key, key_size);
+    case GRUB_TPM2_PROTECTOR_MODE_NV:
+      return grub_tpm2_protector_nv_recover (ctx, key, key_size);
+    default:
+      return GRUB_ERR_BAD_ARGUMENT;
+    }
+}
+
+static grub_err_t
+grub_tpm2_protector_recover_key (grub_uint8_t **key, grub_size_t *key_size)
+{
+  grub_err_t err;
+
+  /* Expect a call to tpm2_protector_init before anybody tries to use us */
+  if (grub_tpm2_protector_ctx.mode == GRUB_TPM2_PROTECTOR_MODE_UNSET)
+    return grub_error (GRUB_ERR_INVALID_COMMAND,
+                       N_("Cannot use TPM2 key protector without initializing "
+                          "it, call tpm2_protector_init first"));
+
+  if (!key)
+    return GRUB_ERR_BAD_ARGUMENT;
+
+  err = grub_tpm2_protector_recover (&grub_tpm2_protector_ctx, key, key_size);
+  if (err)
+    return err;
+
+  return GRUB_ERR_NONE;
+}
+
+
+static grub_err_t
+grub_tpm2_protector_check_args (struct grub_tpm2_protector_context *ctx)
+{
+  if (ctx->mode == GRUB_TPM2_PROTECTOR_MODE_UNSET)
+    ctx->mode = GRUB_TPM2_PROTECTOR_MODE_SRK;
+
+  /* Checks for SRK mode */
+  if (ctx->mode == GRUB_TPM2_PROTECTOR_MODE_SRK && !ctx->keyfile)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT,
+                       N_("In SRK mode, a key file must be specified: "
+                          "--keyfile or -k"));
+
+  if (ctx->mode == GRUB_TPM2_PROTECTOR_MODE_SRK && ctx->nv)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT,
+                       N_("In SRK mode, an NV Index cannot be specified"));
+
+  /* Checks for NV mode */
+  if (ctx->mode == GRUB_TPM2_PROTECTOR_MODE_NV && !ctx->nv)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT,
+                       N_("In NV Index mode, an NV Index must be specified: "
+                           "--nvindex or -n"));
+
+  if (ctx->mode == GRUB_TPM2_PROTECTOR_MODE_NV && ctx->keyfile)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT,
+                       N_("In NV Index mode, a keyfile cannot be specified"));
+
+  if (ctx->mode == GRUB_TPM2_PROTECTOR_MODE_NV && ctx->srk)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT,
+                       N_("In NV Index mode, an SRK cannot be specified"));
+
+  if (ctx->mode == GRUB_TPM2_PROTECTOR_MODE_NV && ctx->asymmetric)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT,
+                       N_("In NV Index mode, an asymmetric key type cannot be "
+                          "specified"));
+
+  /* Defaults assignment */
+  if (!ctx->bank)
+    ctx->bank = TPM_ALG_SHA256;
+
+  if (!ctx->pcr_count)
+    {
+      ctx->pcrs[0] = 7;
+      ctx->pcr_count = 1;
+    }
+
+  if (ctx->mode == GRUB_TPM2_PROTECTOR_MODE_SRK)
+    {
+      if (!ctx->srk)
+        ctx->srk = TPM2_SRK_HANDLE;
+
+      if (!ctx->asymmetric)
+        ctx->asymmetric = TPM_ALG_RSA;
+    }
+
+  return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+grub_tpm2_protector_parse_keyfile (const char *value, const char **keyfile)
+{
+  if (grub_strlen (value) == 0)
+    return GRUB_ERR_BAD_ARGUMENT;
+
+  *keyfile = grub_strdup (value);
+  if (!*keyfile)
+    return grub_error (GRUB_ERR_OUT_OF_MEMORY,
+                       N_("No memory to duplicate keyfile path"));
+
+  return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+grub_tpm2_protector_parse_mode (const char *value,
+                                grub_tpm2_protector_mode_t *mode)
+{
+  if (grub_strcmp (value, "srk") == 0)
+    *mode = GRUB_TPM2_PROTECTOR_MODE_SRK;
+  else if (grub_strcmp (value, "nv") == 0)
+    *mode = GRUB_TPM2_PROTECTOR_MODE_NV;
+  else
+    return grub_error (GRUB_ERR_OUT_OF_RANGE,
+                       N_("Value '%s' is not a valid TPM2 key protector mode"),
+                       value);
+
+  return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+grub_tpm2_protector_init_cmd_handler (grub_extcmd_context_t ctxt, int argc,
+                                 char **args __attribute__ ((unused)))
+{
+  struct grub_arg_list *state = ctxt->state;
+  grub_err_t err;
+
+  if (argc)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT,
+                       N_("The TPM2 key protector does not accept any "
+                          "non-option arguments (i.e., like -o and/or --option 
"
+                          "only)"));
+
+  grub_free ((void *) grub_tpm2_protector_ctx.keyfile);
+  grub_memset (&grub_tpm2_protector_ctx, 0, sizeof (grub_tpm2_protector_ctx));
+
+  if (state[0].set)  /* mode */
+    {
+      err = grub_tpm2_protector_parse_mode (state[0].arg,
+                                            &grub_tpm2_protector_ctx.mode);
+      if (err)
+        return err;
+    }
+
+  if (state[1].set)  /* pcrs */
+    {
+      err = grub_tpm2_protector_parse_pcrs (state[1].arg,
+                                            grub_tpm2_protector_ctx.pcrs,
+                                            
&grub_tpm2_protector_ctx.pcr_count);
+      if (err)
+        return err;
+    }
+
+  if (state[2].set)  /* bank */
+    {
+      err = grub_tpm2_protector_parse_bank (state[2].arg,
+                                            &grub_tpm2_protector_ctx.bank);
+      if (err)
+        return err;
+    }
+
+  if (state[3].set)  /* keyfile */
+    {
+      err = grub_tpm2_protector_parse_keyfile (state[3].arg,
+                                               
&grub_tpm2_protector_ctx.keyfile);
+      if (err)
+        return err;
+    }
+
+  if (state[4].set)  /* srk */
+    {
+      err = grub_tpm2_protector_parse_tpm_handle (state[4].arg,
+                                                  
&grub_tpm2_protector_ctx.srk);
+      if (err)
+        return err;
+    }
+
+  if (state[5].set)  /* asymmetric */
+    {
+      err = grub_tpm2_protector_parse_asymmetric (state[5].arg,
+                                                  
&grub_tpm2_protector_ctx.asymmetric);
+      if (err)
+        return err;
+    }
+
+  if (state[6].set)  /* nvindex */
+    {
+      err = grub_tpm2_protector_parse_tpm_handle (state[6].arg,
+                                                  &grub_tpm2_protector_ctx.nv);
+      if (err)
+        return err;
+    }
+
+  err = grub_tpm2_protector_check_args (&grub_tpm2_protector_ctx);
+
+  /* This command only initializes the protector, so nothing else to do. */
+
+  return err;
+}
+
+static grub_err_t
+grub_tpm2_protector_clear_cmd_handler (grub_extcmd_context_t ctxt 
__attribute__ ((unused)),
+                                       int argc,
+                                       char **args __attribute__ ((unused)))
+{
+  if (argc)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT,
+                       N_("tpm2_key_protector_clear accepts no arguments"));
+
+  grub_free ((void *) grub_tpm2_protector_ctx.keyfile);
+  grub_memset (&grub_tpm2_protector_ctx, 0, sizeof (grub_tpm2_protector_ctx));
+
+  return GRUB_ERR_NONE;
+}
+
+static struct grub_key_protector grub_tpm2_key_protector =
+  {
+    .name = "tpm2",
+    .recover_key = grub_tpm2_protector_recover_key
+  };
+
+GRUB_MOD_INIT (tpm2)
+{
+  grub_tpm2_protector_init_cmd =
+    grub_register_extcmd ("tpm2_key_protector_init",
+                          grub_tpm2_protector_init_cmd_handler, 0,
+                          N_("[-m mode] "
+                             "[-p pcr_list] "
+                             "[-b pcr_bank] "
+                             "[-k sealed_key_file_path] "
+                             "[-s srk_handle] "
+                             "[-a asymmetric_key_type] "
+                             "[-n nv_index]"),
+                          N_("Initialize the TPM2 key protector."),
+                          grub_tpm2_protector_init_cmd_options);
+  grub_tpm2_protector_clear_cmd =
+    grub_register_extcmd ("tpm2_key_protector_clear",
+                          grub_tpm2_protector_clear_cmd_handler, 0, NULL,
+                          N_("Clear the TPM2 key protector if previously 
initialized."),
+                          NULL);
+  grub_key_protector_register (&grub_tpm2_key_protector);
+}
+
+GRUB_MOD_FINI (tpm2)
+{
+  grub_free ((void *) grub_tpm2_protector_ctx.keyfile);
+  grub_memset (&grub_tpm2_protector_ctx, 0, sizeof (grub_tpm2_protector_ctx));
+
+  grub_key_protector_unregister (&grub_tpm2_key_protector);
+  grub_unregister_extcmd (grub_tpm2_protector_clear_cmd);
+  grub_unregister_extcmd (grub_tpm2_protector_init_cmd);
+}
diff --git a/include/grub/tpm2/internal/args.h 
b/include/grub/tpm2/internal/args.h
new file mode 100644
index 0000000..6341fce
--- /dev/null
+++ b/include/grub/tpm2/internal/args.h
@@ -0,0 +1,39 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2022 Microsoft Corporation
+ *
+ *  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/>.
+ */
+
+#ifndef GRUB_TPM2_INTERNAL_ARGS_HEADER
+#define GRUB_TPM2_INTERNAL_ARGS_HEADER 1
+
+#include <grub/err.h>
+#include <grub/tpm2/tpm2.h>
+
+grub_err_t
+grub_tpm2_protector_parse_pcrs (char *value, grub_uint8_t *pcrs,
+                                grub_uint8_t *pcr_count);
+
+grub_err_t
+grub_tpm2_protector_parse_asymmetric (const char *value,
+                                      TPM_ALG_ID *asymmetric);
+
+grub_err_t
+grub_tpm2_protector_parse_bank (const char *value, TPM_ALG_ID *bank);
+
+grub_err_t
+grub_tpm2_protector_parse_tpm_handle (const char *value, TPM_HANDLE *handle);
+
+#endif /* ! GRUB_TPM2_INTERNAL_ARGS_HEADER */
-- 
1.8.3.1