diff mbox series

[v2,04/10] security: keys: trusted: Allow storage of PCR values in creation data

Message ID 20220823152108.v2.4.I32591db064b6cdc91850d777f363c9d05c985b39@changeid (mailing list archive)
State Superseded, archived
Headers show
Series Encrypted Hibernation | expand

Commit Message

Evan Green Aug. 23, 2022, 10:25 p.m. UTC 
From: Matthew Garrett <matthewgarrett@google.com>

When TPMs generate keys, they can also generate some information
describing the state of the PCRs at creation time. This data can then
later be certified by the TPM, allowing verification of the PCR values.
This allows us to determine the state of the system at the time a key
was generated. Add an additional argument to the trusted key creation
options, allowing the user to provide the set of PCRs that should have
their values incorporated into the creation data.

From: Matthew Garrett <mjg59@google.com>
Signed-off-by: Matthew Garrett <mjg59@google.com>

Signed-off-by: Evan Green <evgreen@chromium.org>

---
Matthew's original version of this patch is at:
https://patchwork.kernel.org/patch/12096503/

(no changes since v1)

 .../security/keys/trusted-encrypted.rst       |  4 +++
 include/keys/trusted-type.h                   |  1 +
 security/keys/trusted-keys/trusted_tpm1.c     |  9 +++++++
 security/keys/trusted-keys/trusted_tpm2.c     | 25 +++++++++++++++++--
 4 files changed, 37 insertions(+), 2 deletions(-)

Comments

Ben Boeckel Aug. 24, 2022, 11:56 a.m. UTC | #1 
On Tue, Aug 23, 2022 at 15:25:20 -0700, Evan Green wrote:
> diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
> index 0bfb4c33974890..dc9e11bb4824da 100644
> --- a/Documentation/security/keys/trusted-encrypted.rst
> +++ b/Documentation/security/keys/trusted-encrypted.rst
> @@ -199,6 +199,10 @@ Usage::
>         policyhandle= handle to an authorization policy session that defines the
>                       same policy and with the same hash algorithm as was used to
>                       seal the key.
> +       creationpcrs= hex integer representing the set of PCR values to be
> +                     included in the PCR creation data. The bit corresponding
> +		     to each PCR should be 1 to be included, 0 to be ignored.
> +		     TPM2 only.

There's inconsistent whitespace here. Given the context, I suspect the
tabs should be expanded to spaces.

As for the docs themselves, this might preferrably mention how large
this is supposed to be. It seems to be limited to 32bits by the code.
What happens if fewer are provided? More? Will there always be at most
32 PCR values? Also, how are the bits interpreted? I presume bit 0 is
for PCR value 0?

Thanks for including docs.

Thanks,

--Ben
Evan Green Aug. 24, 2022, 5:34 p.m. UTC | #2 
On Wed, Aug 24, 2022 at 4:56 AM Ben Boeckel <me@benboeckel.net> wrote:
>
> On Tue, Aug 23, 2022 at 15:25:20 -0700, Evan Green wrote:
> > diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
> > index 0bfb4c33974890..dc9e11bb4824da 100644
> > --- a/Documentation/security/keys/trusted-encrypted.rst
> > +++ b/Documentation/security/keys/trusted-encrypted.rst
> > @@ -199,6 +199,10 @@ Usage::
> >         policyhandle= handle to an authorization policy session that defines the
> >                       same policy and with the same hash algorithm as was used to
> >                       seal the key.
> > +       creationpcrs= hex integer representing the set of PCR values to be
> > +                     included in the PCR creation data. The bit corresponding
> > +                  to each PCR should be 1 to be included, 0 to be ignored.
> > +                  TPM2 only.
>
> There's inconsistent whitespace here. Given the context, I suspect the
> tabs should be expanded to spaces.
>
> As for the docs themselves, this might preferrably mention how large
> this is supposed to be. It seems to be limited to 32bits by the code.
> What happens if fewer are provided? More? Will there always be at most
> 32 PCR values? Also, how are the bits interpreted? I presume bit 0 is
> for PCR value 0?

Makes sense, I'll pin down the specification a bit better here and fix
up the spacing.

>
> Thanks for including docs.

Thanks for looking at them!

-Evan
diff mbox series

Patch

diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
index 0bfb4c33974890..dc9e11bb4824da 100644
--- a/Documentation/security/keys/trusted-encrypted.rst
+++ b/Documentation/security/keys/trusted-encrypted.rst
@@ -199,6 +199,10 @@  Usage::
        policyhandle= handle to an authorization policy session that defines the
                      same policy and with the same hash algorithm as was used to
                      seal the key.
+       creationpcrs= hex integer representing the set of PCR values to be
+                     included in the PCR creation data. The bit corresponding
+		     to each PCR should be 1 to be included, 0 to be ignored.
+		     TPM2 only.
 
 "keyctl print" returns an ascii hex copy of the sealed key, which is in standard
 TPM_STORED_DATA format.  The key length for new keys are always in bytes.
diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h
index 209086fed240a5..8523d41507b2a4 100644
--- a/include/keys/trusted-type.h
+++ b/include/keys/trusted-type.h
@@ -54,6 +54,7 @@  struct trusted_key_options {
 	uint32_t policydigest_len;
 	unsigned char policydigest[MAX_DIGEST_SIZE];
 	uint32_t policyhandle;
+	uint32_t creation_pcrs;
 };
 
 struct trusted_key_ops {
diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
index aa108bea6739b3..2975827c01bec0 100644
--- a/security/keys/trusted-keys/trusted_tpm1.c
+++ b/security/keys/trusted-keys/trusted_tpm1.c
@@ -713,6 +713,7 @@  enum {
 	Opt_hash,
 	Opt_policydigest,
 	Opt_policyhandle,
+	Opt_creationpcrs,
 };
 
 static const match_table_t key_tokens = {
@@ -725,6 +726,7 @@  static const match_table_t key_tokens = {
 	{Opt_hash, "hash=%s"},
 	{Opt_policydigest, "policydigest=%s"},
 	{Opt_policyhandle, "policyhandle=%s"},
+	{Opt_creationpcrs, "creationpcrs=%s"},
 	{Opt_err, NULL}
 };
 
@@ -858,6 +860,13 @@  static int getoptions(char *c, struct trusted_key_payload *pay,
 				return -EINVAL;
 			opt->policyhandle = handle;
 			break;
+		case Opt_creationpcrs:
+			if (!tpm2)
+				return -EINVAL;
+			res = kstrtoint(args[0].from, 16, &opt->creation_pcrs);
+			if (res < 0)
+				return -EINVAL;
+			break;
 		default:
 			return -EINVAL;
 		}
diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 1f166d4fa307a9..1d1470b880ca01 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -389,7 +389,7 @@  int tpm2_seal_trusted(struct tpm_chip *chip,
 	struct tpm_buf buf;
 	u32 hash;
 	u32 flags;
-	int i;
+	int i, j;
 	int rc;
 
 	for (i = 0; i < ARRAY_SIZE(tpm2_hash_map); i++) {
@@ -458,7 +458,28 @@  int tpm2_seal_trusted(struct tpm_chip *chip,
 	tpm_buf_append_u16(&buf, 0);
 
 	/* creation PCR */
-	tpm_buf_append_u32(&buf, 0);
+	if (options->creation_pcrs) {
+		/* One bank */
+		tpm_buf_append_u32(&buf, 1);
+		/* Which bank to use */
+		tpm_buf_append_u16(&buf, hash);
+		/* Length of the PCR bitmask */
+		tpm_buf_append_u8(&buf, 3);
+		/* PCR bitmask */
+		for (i = 0; i < 3; i++) {
+			char tmp = 0;
+
+			for (j = 0; j < 8; j++) {
+				char bit = (i * 8) + j;
+
+				if (options->creation_pcrs & (1 << bit))
+					tmp |= (1 << j);
+			}
+			tpm_buf_append_u8(&buf, tmp);
+		}
+	} else {
+		tpm_buf_append_u32(&buf, 0);
+	}
 
 	if (buf.flags & TPM_BUF_OVERFLOW) {
 		rc = -E2BIG;