Extend the ima_measurement --pcrs option to support per-bank pcr files.
The extended syntax is "--pcrs algorithm,pathname". If no algorithm
is specified, it defaults to sha1 as before. Multiple --pcrs options
are now supported, one per bank of PCRs. The file format remains
unchanged. If --pcrs is specified, only try to read PCRs from the
specified file(s); do not fall back to trying to read from sysfs
or the TPM itself in this case since the user requested use of
the files.
Create per-bank pcr files, depends on "tpm: add sysfs exports for all
banks of PCR registers" kernel patch:
$ cat tpm2pcrread.sh
#!/bin/sh
for alg in sha1 sha256
do
rm -f pcr-$alg
pcr=0;
while [ $pcr -lt 24 ];
do
printf "PCR-%02d: " $pcr >> pcr-$alg;
cat /sys/class/tpm/tpm0/pcr-$alg/$pcr >> pcr-$alg;
pcr=$[$pcr+1];
done
done
$ sh ./tpm2pcrread.sh
Pass only the sha1 PCRs to evmctl defaulting to sha1:
$ sudo evmctl ima_measurement --pcrs pcr-sha1 /sys/kernel/security/integrity/ima/binary_runtime_measurements
Pass only the sha1 PCRs to evmctl with explicit selection of sha1:
$ sudo evmctl ima_measurement --pcrs sha1,pcr-sha1 /sys/kernel/security/integrity/ima/binary_runtime_measurements
Pass both sha1 and sha256 PCRs to evmctl:
$ sudo evmctl ima_measurement --pcrs sha1,pcr-sha1 --pcrs sha256,pcr-sha256 /sys/kernel/security/integrity/ima/binary_runtime_measurements
Signed-off-by: Stephen Smalley <stephen.smalley.work@xxxxxxxxx>
---
v4 updates the usage in the README and usage message, reduces MAX_NPCRFILE
to 2 (for sha1 and sha256) and changes the buffer size to
MAX_DIGEST_SIZE * 2 + 8 for the lines read from the pcrs file(s).
One thing that is unclear to me is correct/expected usage of the
--verify and --validate options to evmctl ima_measurement. For an
appraisal of a remote attestation, when would one NOT want to use
--verify (i.e. doesn't lack of --verify render the result insecure)
and when would one want to use --validate (i.e. doesn't use of --validate
render the result insecure)? And shouldn't the default in both cases
be the more secure case (i.e. verify = 1, validate = 0)? The naming of
--validate is also confusing since one might expect it to mean
to validate/check the result as opposed to ignore violations?
README | 4 +-
src/evmctl.c | 170 +++++++++++++++++++++++++++++++++------------------
src/imaevm.h | 2 +-
3 files changed, 113 insertions(+), 63 deletions(-)
diff --git a/README b/README
index 596b3b0..73b38a1 100644
--- a/README
+++ b/README
@@ -31,7 +31,7 @@ COMMANDS
ima_sign [--sigfile] [--key key] [--pass password] file
ima_verify file
ima_hash file
- ima_measurement [--validate] [--verify] [--verify-sig [--key "key1, key2, ..."]] [--pcrs file] file
+ ima_measurement [--validate] [--verify] [--verify-sig [--key "key1, key2, ..."]] [--pcrs [hash-algorithm,]file [--pcrs hash-algorithm,file] ...] file
ima_fix [-t fdsxm] path
sign_hash [--key key] [--pass password]
hmac [--imahash | --imasig ] file
@@ -59,7 +59,7 @@ OPTIONS
--m32 force EVM hmac/signature for 32 bit target system
--m64 force EVM hmac/signature for 64 bit target system
--engine e preload OpenSSL engine e (such as: gost)
- --pcrs file containing TPM 1.2 pcrs
+ --pcrs file containing TPM pcrs, one per hash-algorithm/bank
--validate ignore ToMToU measurement violations
--verify verify the template data digest
--verify-sig verify the file signature based on the file hash, both
diff --git a/src/evmctl.c b/src/evmctl.c
index faddc3c..448e4a9 100644
--- a/src/evmctl.c
+++ b/src/evmctl.c
@@ -160,7 +160,10 @@ struct tpm_bank_info {
uint8_t pcr[NUM_PCRS][MAX_DIGEST_SIZE];
};
-static char *pcrfile;
+/* One --pcrs file per hash-algorithm/bank */
+#define MAX_PCRFILE 2
+static char *pcrfile[MAX_PCRFILE];
+static unsigned npcrfile;
static int bin2file(const char *file, const char *ext, const unsigned char *data, int len)
{
@@ -1373,55 +1376,6 @@ static int cmd_ima_clear(struct command *cmd)
return do_cmd(cmd, ima_clear);
}
-static char *pcrs = "/sys/class/tpm/tpm0/device/pcrs"; /* Kernels >= 4.0 */
-static char *misc_pcrs = "/sys/class/misc/tpm0/device/pcrs";
-
-/* Read all of the TPM 1.2 PCRs */
-static int tpm_pcr_read(struct tpm_bank_info *tpm_banks, int len)
-{
- struct stat s;
- FILE *fp = NULL;
- char *p, pcr_str[8], buf[70]; /* length of the TPM string */
- int result = -1;
- int i = 0;
-
- /* Use the provided TPM 1.2 pcrs file */
- if (pcrfile) {
- if (stat(pcrfile, &s) == -1) {
- errno = 0;
- return 1;
- }
-
- if (!S_ISREG(s.st_mode)) {
- log_info("TPM 1.2 PCR file: not a regular file or link to regular file\n");
- return 1;
- }
-
- fp = fopen(pcrfile, "r");
- }
-
- if (!fp)
- fp = fopen(pcrs, "r");
-
- if (!fp)
- fp = fopen(misc_pcrs, "r");
-
- if (!fp)
- return -1;
-
- for (;;) {
- p = fgets(buf, sizeof(buf), fp);
- if (!p || i > 99)
- break;
- sprintf(pcr_str, "PCR-%2.2d", i);
- if (!strncmp(p, pcr_str, 6))
- hex2bin(tpm_banks[0].pcr[i++], p + 7, len);
- result = 0;
- }
- fclose(fp);
- return result;
-}
-
#define TCG_EVENT_NAME_LEN_MAX 255
struct template_entry {
@@ -1829,20 +1783,108 @@ static void extend_tpm_banks(struct template_entry *entry, int num_banks,
#endif
}
-/* Read TPM 1.2 PCRs */
-static int read_tpm_pcrs(int num_banks, struct tpm_bank_info *tpm_banks)
+static int read_one_bank(struct tpm_bank_info *tpm_bank, FILE *fp)
{
- int i;
+ char *p, pcr_str[8], buf[MAX_DIGEST_SIZE * 2 + 8];
+ int i = 0;
+ int result = -1;
+ for (;;) {
+ p = fgets(buf, sizeof(buf), fp);
+ if (!p || i >= NUM_PCRS)
+ break;
+ sprintf(pcr_str, "PCR-%2.2d", i);
+ if (!strncmp(p, pcr_str, 6))
+ hex2bin(tpm_bank->pcr[i++], p + 7, tpm_bank->digest_size);
+ result = 0;
+ }
+ return result;
+}
+
+static char *pcrs = "/sys/class/tpm/tpm0/device/pcrs"; /* Kernels >= 4.0 */
+static char *misc_pcrs = "/sys/class/misc/tpm0/device/pcrs";
+
+/* Read one of the TPM 1.2 sysfs files if present */
+static int read_sysfs_pcrs(int num_banks, struct tpm_bank_info *tpm_banks)
+{
+ FILE *fp;
+ int i, result;
- if (tpm_pcr_read(tpm_banks, SHA_DIGEST_LENGTH)) {
- log_debug("Failed to read TPM 1.2 PCRs.\n");
+ fp = fopen(pcrs, "r");
+ if (!fp)
+ fp = fopen(misc_pcrs, "r");
+ if (!fp)
return -1;
- }
+ result = read_one_bank(&tpm_banks[0], fp);
+ fclose(fp);
+ if (result < 0)
+ return result;
tpm_banks[0].supported = 1;
for (i = 1; i < num_banks; i++)
tpm_banks[i].supported = 0;
return 0;
+
+}
+
+/* Read PCRs from per-bank file(s) specified via --pcrs */
+static int read_file_pcrs(int num_banks, struct tpm_bank_info *tpm_banks)
+{
+ struct stat s;
+ FILE *fp;
+ char *p;
+ const char *alg, *path;
+ int i, j, bank, result;
+
+ for (i = 0; i < num_banks; i++)
+ tpm_banks[i].supported = 0;
+
+ for (i = 0; i < npcrfile; i++) {
+ p = strchr(pcrfile[i], ',');
+ if (p) {
+ *p = 0;
+ alg = pcrfile[i];
+ path = ++p;
+ } else {
+ alg = "sha1";
+ path = pcrfile[i];
+ }
+
+ bank = -1;
+ for (j = 0; j < num_banks; j++) {
+ if (!strcmp(tpm_banks[j].algo_name, alg)) {
+ bank = j;
+ break;
+ }
+ }
+ if (bank < 0) {
+ log_err("Unknown algorithm '%s'\n", alg);
+ return -1;
+ }
+
+ if (stat(path, &s) == -1) {
+ log_err("Could not stat '%s'\n", path);
+ return -1;
+ }
+
+ if (!S_ISREG(s.st_mode)) {
+ log_err("PCR file: not a regular file or link to regular file\n");
+ return -1;
+ }
+
+ fp = fopen(path, "r");
+ if (!fp) {
+ log_err("Could not open '%s'\n", path);
+ return -1;
+ }
+
+ result = read_one_bank(&tpm_banks[bank], fp);
+ fclose(fp);
+ if (result < 0)
+ return result;
+ tpm_banks[bank].supported = 1;
+ }
+
+ return 0;
}
/*
@@ -1857,8 +1899,12 @@ static int read_tpm_banks(int num_banks, struct tpm_bank_info *bank)
int i, j;
int err;
- /* First try reading PCRs from exported TPM 1.2 sysfs file */
- if (read_tpm_pcrs(num_banks, bank) == 0)
+ /* If --pcrs was specified, read only from the specified file(s) */
+ if (npcrfile)
+ return read_file_pcrs(num_banks, bank);
+
+ /* Else try reading PCRs from the sysfs file if present */
+ if (read_sysfs_pcrs(num_banks, bank) == 0)
return 0;
/* Any userspace applications available for reading TPM 2.0 PCRs? */
@@ -2440,7 +2486,7 @@ struct command cmds[] = {
{"ima_verify", cmd_verify_ima, 0, "file", "Verify IMA signature (for debugging).\n"},
{"ima_setxattr", cmd_setxattr_ima, 0, "[--sigfile file]", "Set IMA signature from sigfile\n"},
{"ima_hash", cmd_hash_ima, 0, "file", "Make file content hash.\n"},
- {"ima_measurement", cmd_ima_measurement, 0, "[--validate] [--verify] [--verify-sig [--key key1, key2, ...]] [--pcrs file] file", "Verify measurement list (experimental).\n"},
+ {"ima_measurement", cmd_ima_measurement, 0, "[--validate] [--verify] [--verify-sig [--key key1, key2, ...]] [--pcrs [hash-algorithm,]file [--pcrs hash-algorithm,file] ...] file", "Verify measurement list (experimental).\n"},
{"ima_boot_aggregate", cmd_ima_bootaggr, 0, "[file]", "Calculate per TPM bank boot_aggregate digests\n"},
{"ima_fix", cmd_ima_fix, 0, "[-t fdsxm] path", "Recursively fix IMA/EVM xattrs in fix mode.\n"},
{"ima_clear", cmd_ima_clear, 0, "[-t fdsxm] path", "Recursively remove IMA/EVM xattrs.\n"},
@@ -2667,7 +2713,11 @@ int main(int argc, char *argv[])
verify = 1;
break;
case 143:
- pcrfile = optarg;
+ if (npcrfile >= MAX_PCRFILE) {
+ log_err("too many --pcrfile options\n");
+ exit(1);
+ }
+ pcrfile[npcrfile++] = optarg;
break;
case '?':
exit(1);
diff --git a/src/imaevm.h b/src/imaevm.h
index 3f1db97..4503919 100644
--- a/src/imaevm.h
+++ b/src/imaevm.h
@@ -203,7 +203,7 @@ struct RSA_ASN1_template {
size_t size;
};
-#define NUM_PCRS 20
+#define NUM_PCRS 24
#define DEFAULT_PCR 10
extern struct libimaevm_params imaevm_params;
--
2.25.1
