On Thu, 2020-07-23 at 15:33 -0400, Stephen Smalley wrote:
> 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.
>
> 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 --validate
>
> 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 --validate
>
> Pass both sha1 and sha2 PCRs to evmctl:
> $ sudo evmctl ima_measurement --pcrs sha1,pcr-sha1 --pcrs sha256,pcr-sha256 /sys/kernel/security/integrity/ima/binary_runtime_measurements --validate
>
> NB The file parser could be improved to be more robust but I left the
> existing code unchanged from the code to read the TPM 1.2 sysfs file other
> than generalizing it to support loading other banks.
Agreed. As a separate patch, please feel free to update the file
parser.
>
> NB The error handling is IMHO wrong; if any error occurs during handling of
> the --pcrs option(s), evmctl will try to fall back to reading the PCRs in
> some other way. I think these should be fatal errors but left it as it
> was for the TPM 1.2 sysfs file.
>
> Signed-off-by: Stephen Smalley <stephen.smalley.work@xxxxxxxxx>
Thank you.
<snip>
> @@ -1829,16 +1783,100 @@ static void extend_tpm_banks(struct template_entry *entry, int num_banks,
> #endif
> }
>
> -/* Read TPM 1.2 PCRs */
> +static int read_one_bank(struct tpm_bank_info *tpm_bank, FILE *fp)
> +{
> + char *p, pcr_str[8], buf[80];
> + int i = 0;
> + int result = -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_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 all of the TPM PCRs */
> static int read_tpm_pcrs(int num_banks, struct tpm_bank_info *tpm_banks)
> {
> - int i;
> + struct stat s;
> + FILE *fp = NULL;
> + char *p;
> + const char *alg, *path;
> + int i = 0, j;
> + int bank, result;
> +
> + /* Use the provided TPM bank pcr file(s) */
> + if (npcrfile) {
> + 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];
> + }
>
> - if (tpm_pcr_read(tpm_banks, SHA_DIGEST_LENGTH)) {
> - log_debug("Failed to read TPM 1.2 PCRs.\n");
> - return -1;
> + 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("TPM 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;
> }
Previously on failure to read the --pcrs TPM 1.2 file, it attempted to
then read the TPM 1.2 sysfs file. Changing it like this is fine. I
agree with NB 2 - either read the PCR files or the TPM PCRs directly,
not both. Perhaps make that a separate patch either before or after
this one.
I appreciate your limiting the changes to simplify review. With
reading either the PCR files or the sysfs files, can we get rid of the
npcrfile indentation above?
if (!npcrfile)
read_sysfs_pcrs()
Mimi
> + /* Read the TPM 1.2 sysfs file */
> + 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;
