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* [PATCH v3] ima-evm-utils: use tsspcrread to read the TPM 2.0 PCRs
@ 2019-07-23 20:27 Mimi Zohar
  2019-07-23 20:44 ` Bruno E. O. Meneguele
  2019-07-24  7:16 ` Petr Vorel
  0 siblings, 2 replies; 3+ messages in thread
From: Mimi Zohar @ 2019-07-23 20:27 UTC (permalink / raw)
  To: linux-integrity
  Cc: Vitaly Chikunov, Petr Vorel, Bruno E . O . Meneguele,
	Dmitry Eremin-Solenikov, Mimi Zohar

The kernel does not expose the crypto agile TPM 2.0 PCR banks to
userspace like it exposes PCRs for TPM 1.2.  As a result, a userspace
application is required to read PCRs.

This patch adds tsspcrread support for reading the TPM 2.0 PCRs.
tsspcrread is one application included in the ibmtss package.

Sample error messages:
Failed to read PCRs: (tsspcrread failed: No such file or directory)
Failed to read PCRs: (TSS_Dev_Open: Error opening /dev/tpmrm0)

Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
---
Changelog v3:
- Suggested by Vitaly, replace snprintf() & strdup() with asprintf().

Changelog v2:
- Fix "errmsg" not always being initialized within tpm_pcr_read2().
  Reported by Bruno.
- Shortened error msg length.
- Renamed tpm_pcr_read2() to tpm2_pcr_read().
- Included Petr Vorel's autotool change, which looks for tsspcrread,
  rather than the tss library.

Changelog v1:
- Based on Vitaly's review, test the popen "cmd"  return code.  Use
pclose to determine if the result of the popen command succeeded or
failed.  Removed the now unneeded checking for spaces.
- Dynamically allocated the error msg and other changes based on
Vitaly's review.
- Based on Bruno's review, reverted the return code change.  At some
point, we'll need to re-visit the return codes in general.


 configure.ac |  7 +++++++
 src/evmctl.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 60 insertions(+), 4 deletions(-)

diff --git a/configure.ac b/configure.ac
index 9beb4b6c2377..3fc63b367c91 100644
--- a/configure.ac
+++ b/configure.ac
@@ -7,6 +7,7 @@ AC_CONFIG_HEADERS([config.h])
 AC_CONFIG_MACRO_DIR([m4])
 
 AC_CANONICAL_HOST
+AC_USE_SYSTEM_EXTENSIONS
 
 # Checks for programs.
 AC_PROG_CC
@@ -29,6 +30,11 @@ AC_SUBST(KERNEL_HEADERS)
 AC_CHECK_HEADER(unistd.h)
 AC_CHECK_HEADERS(openssl/conf.h)
 
+AC_CHECK_PROG(TSSPCRREAD, [tsspcrread], yes, no)
+if test "x$TSSPCRREAD" = "xyes"; then
+	AC_DEFINE(HAVE_TSSPCRREAD, 1, [Define to 1 if you have tsspcrread binary installed])],
+fi
+
 AC_CHECK_HEADERS(sys/xattr.h, , [AC_MSG_ERROR([sys/xattr.h header not found. You need the c-library development package.])])
 AC_CHECK_HEADERS(keyutils.h, , [AC_MSG_ERROR([keyutils.h header not found. You need the libkeyutils development package.])])
 
@@ -71,4 +77,5 @@ echo
 echo	"Configuration:"
 echo	"          debug: $pkg_cv_enable_debug"
 echo	"   openssl-conf: $enable_openssl_conf"
+echo	"     tsspcrread: $TSSPCRREAD"
 echo
diff --git a/src/evmctl.c b/src/evmctl.c
index 9e0926f10404..3289061fe8d2 100644
--- a/src/evmctl.c
+++ b/src/evmctl.c
@@ -1383,10 +1383,8 @@ static int tpm_pcr_read(int idx, uint8_t *pcr, int len)
 	if (!fp)
 		fp = fopen(misc_pcrs, "r");
 
-	if (!fp) {
-		log_err("Unable to open %s or %s\n", pcrs, misc_pcrs);
+	if (!fp)
 		return -1;
-	}
 
 	for (;;) {
 		p = fgets(buf, sizeof(buf), fp);
@@ -1402,6 +1400,43 @@ static int tpm_pcr_read(int idx, uint8_t *pcr, int len)
 	return result;
 }
 
+#ifdef HAVE_TSSPCRREAD
+static int tpm2_pcr_read(int idx, uint8_t *hwpcr, int len, char **errmsg)
+{
+	FILE *fp;
+	char pcr[100];	/* may contain an error */
+	char cmd[50];
+	int ret;
+
+	sprintf(cmd, "tsspcrread -halg sha1 -ha %d -ns 2> /dev/null", idx);
+	fp = popen(cmd, "r");
+	if (!fp) {
+		ret = asprintf(errmsg, "popen failed: %s", strerror(errno));
+		if (ret == -1)	/* the contents of errmsg is undefined */
+			*errmsg = NULL;
+		return -1;
+	}
+
+	if (fgets(pcr, sizeof(pcr), fp) == NULL) {
+		ret = asprintf(errmsg, "tsspcrread failed: %s",
+			       strerror(errno));
+		if (ret == -1)	/* the contents of errmsg is undefined */
+			*errmsg = NULL;
+		ret = pclose(fp);
+		return -1;
+	}
+
+	/* get the popen "cmd" return code */
+	ret = pclose(fp);
+	if (!ret)
+		hex2bin(hwpcr, pcr, SHA_DIGEST_LENGTH);
+	else
+		*errmsg = strndup(pcr, strlen(pcr) - 1); /* remove newline */
+
+	return ret;
+}
+#endif
+
 #define TCG_EVENT_NAME_LEN_MAX	255
 
 struct template_entry {
@@ -1658,8 +1693,22 @@ static int ima_measurement(const char *file)
 		log_info("PCRAgg %.2d: ", i);
 		log_dump(pcr[i], SHA_DIGEST_LENGTH);
 
-		if (tpm_pcr_read(i, hwpcr, sizeof(hwpcr)))
+		if (tpm_pcr_read(i, hwpcr, sizeof(hwpcr))) {
+#ifdef HAVE_TSSPCRREAD
+			char *errmsg = NULL;
+
+			err = tpm2_pcr_read(i, hwpcr, sizeof(hwpcr), &errmsg);
+			if (err) {
+				log_info("Failed to read PCRs: (%s)\n", errmsg);
+				free(errmsg);
+				exit(1);
+			}
+#else
+			log_info("Failed to read TPM 1.2 PCRs.\n");
 			exit(1);
+#endif
+		}
+
 		log_info("HW PCR-%d: ", i);
 		log_dump(hwpcr, sizeof(hwpcr));
 
-- 
2.7.5


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2019-07-23 20:27 [PATCH v3] ima-evm-utils: use tsspcrread to read the TPM 2.0 PCRs Mimi Zohar
2019-07-23 20:44 ` Bruno E. O. Meneguele
2019-07-24  7:16 ` Petr Vorel

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