[PATCH v8 17/22] protectors: Implement NV index

[Gary Lin]

From: Patrick Colp <patrick.colp@oracle.com>

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. grub2_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 rsa -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>
---
 grub-core/tpm2/module.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/grub-core/tpm2/module.c b/grub-core/tpm2/module.c
index 0cbfd06e8..00b401bd5 100644
--- a/grub-core/tpm2/module.c
+++ b/grub-core/tpm2/module.c
@@ -834,12 +834,27 @@ 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;
+  TPM_HANDLE sealed_handle = ctx->nv;
+  tpm2key_policy_t policy_seq = NULL;
+  grub_err_t err;
+
+  /* Create a basic policy sequence based on the given PCR selection */
+  err = grub_tpm2_protector_simple_policy_seq (ctx, &policy_seq);
+  if (err != GRUB_ERR_NONE)
+    goto exit;
+
+  err = grub_tpm2_protector_unseal (policy_seq, sealed_handle, key, key_size);
+
+  /* Pop error messages on success */
+  if (err == GRUB_ERR_NONE)
+    while (grub_error_pop ());
+
+exit:
+  TPM2_FlushContext (sealed_handle);
 
-  return grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
-                    N_("NV Index mode is not implemented yet"));
+  grub_tpm2key_free_policy_seq (policy_seq);
+
+  return err;
 }
 
 static grub_err_t
-- 
2.35.3