RE: [PATCH RESEND v4 1/1] tpm: add sysfs exports for all banks of PCR registers

-----Original Message-----
From: James Bottomley <James.Bottomley@HansenPartnership.com>
Sent: Monday, November 30, 2020 1:54 PM
To: Elliott, Robert (Servers) <redacted>; linux-
integrity@vger.kernel.org
Cc: Mimi Zohar <zohar@linux.ibm.com>; Jarkko Sakkinen
[off-list ref]; linux-api@vger.kernel.org
Subject: Re: [PATCH RESEND v4 1/1] tpm: add sysfs exports for all
banks of PCR registers

On Mon, 2020-11-30 at 19:00 +0000, Elliott, Robert (Servers) wrote:

quoted

...

quoted

+ * The first argument is the TPM algorithm id and the second is
the
+ * hash used as both the suffix and the group name.  Note: the
group
+ * name is a directory in the top level tpm class with the name
+ * pcr-<hash>, so it must not clash with any other names already
+ * in the sysfs directory.
+ */
+PCR_ATTR_BUILD(TPM_ALG_SHA1, sha1);
+PCR_ATTR_BUILD(TPM_ALG_SHA256, sha256);
+PCR_ATTR_BUILD(TPM_ALG_SHA384, sha384);
+PCR_ATTR_BUILD(TPM_ALG_SHA512, sha512);
+PCR_ATTR_BUILD(TPM_ALG_SM3_256, sm3);

The latest PC Client Platform TPM Profile and TPM 2.0 Part 2
Structures specs also define codes for three SHA-3 hash algorithms:
  TPM_ALG_SHA3_256
  TPM_ALG_SHA3_384
  TPM_ALG_SHA3_512

this is PTP 1.05 which was published this September?  The basic
reason
is it wasn't there when this patch was first published, but they can
always be added ... the whole idea is to be extensible.

Yes, they are in
* TCG PC Client Platform TPM Profile Specification for TPM 2.0
  Version 1.05, Revision 14, 4 September 2020
* Trusted Platform Module Library Part 2: Structures
  Family 2.0, Level 00 Revision 1.59, 8 November 2019

I don't know if anyone has started implementing SHA-3 for PCRs.

quoted

...

quoted

+
+	/* add one group for each bank hash */
+	for (i = 0; i < chip->nr_allocated_banks; i++) {
+		switch (chip->allocated_banks[i].alg_id) {
+		case TPM_ALG_SHA1:
+			chip->groups[chip->groups_cnt++] =
&pcr_group_sha1;
+			break;
+		case TPM_ALG_SHA256:
+			chip->groups[chip->groups_cnt++] =
&pcr_group_sha256;
+			break;
+		case TPM_ALG_SHA384:
+			chip->groups[chip->groups_cnt++] =
&pcr_group_sha384;
+			break;
+		case TPM_ALG_SHA512:
+			chip->groups[chip->groups_cnt++] =
&pcr_group_sha512;
+			break;
+		case TPM_ALG_SM3_256:
+			chip->groups[chip->groups_cnt++] =
&pcr_group_sm3;
+			break;
+		default:
+			/*
+			 * If this warning triggers, send a patch to
+			 * add both a PCR_ATTR_BUILD() macro above for
+			 * the missing algorithm as well as an
+			 * additional case in this switch statement.
+			 */
+			WARN(1, "TPM with unsupported bank algorthm
0x%04x",
+			     chip->allocated_banks[i].alg_id);

algorithm is missing the letter i.

Yes, I'll fix that.

quoted

It might help to print the bank id (variable i) as well.

I'm not sure how it helps the user.  We deliberately hide the bank
numbers because all banks in sysfs are referred to by hash ... how
would exposing the bank number here help?

I just noticed the WARN inside the for loop and worried about
spewing a lot of similar messages, each with long stack traces.

nr_allocated_banks shouldn't be very large, though, so there's
probably nothing to be concerned about.

Maybe consider dev_warn instead of WARN? That would indicate which
TPM has the unsupported algorithm, which could be useful, but avoid
the stack dump, which might not be useful (except that it is more
likely to be reported back to kernel developers).