Re: [ima-evm-utils][PATCH] Limit comparing the calculated PCR value to just a single bank

[Stefan Berger <stefanb@linux.ibm.com>]

On 2/9/21 11:41 AM, Mimi Zohar wrote:
> TPM 2.0 banks may be extended either with a padded SHA1 hash or more
> recently with a per TPM bank calculated hash.  If the measurement list
> is carried across kexec, the original kernel might extend the TPM
> differently than the new kernel.
>
> Support for verifying a mixed IMA measurement list is not supported.  To
> permit verifying just the SHA1 bank, specify "--verify-bank=sha1" on the
> command line.
>
> Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
> ---
>   src/evmctl.c | 17 ++++++++++++++++-
>   1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/src/evmctl.c b/src/evmctl.c
> index f7ffe388ef4f..051c218cc8b5 100644
> --- a/src/evmctl.c
> +++ b/src/evmctl.c
> @@ -125,6 +125,7 @@ static char *caps_str;
>   static char *ima_str;
>   static char *selinux_str;
>   static char *search_type;
> +static char *verify_bank;
>   static int verify_list_sig;
>   static int recursive;
>   static int msize;
> @@ -2011,6 +2012,16 @@ static int ima_measurement(const char *file)
>   	pseudo_banks_mask = (1 << num_banks) - 1;
>   	pseudo_padded_banks_mask = pseudo_banks_mask;
>   
> +	/* Instead of verifying all the banks, only verify a single bank */
> +	for (c = 0; c < num_banks; c++) {
> +		if (verify_bank
> +		    && strcmp(pseudo_padded_banks[c].algo_name, verify_bank)) {
> +			pseudo_banks_mask ^= (1 << c);
> +			pseudo_padded_banks_mask ^= (1 << c);
> +			break;
> +		}
> +	}
> +
>   	while (fread(&entry.header, sizeof(entry.header), 1, fp)) {
>   		entry_num++;
>   		if (entry.header.name_len > TCG_EVENT_NAME_LEN_MAX) {
> @@ -2537,7 +2548,7 @@ 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, "[--ignore-violations] [--verify-sig [--key key1, key2, ...]] [--pcrs [hash-algorithm,]file [--pcrs hash-algorithm,file] ...] file", "Verify measurement list (experimental).\n"},
> +	{"ima_measurement", cmd_ima_measurement, 0, "[--ignore-violations] [--verify-sig [--key key1, key2, ...]] [--pcrs [hash-algorithm,]file [--pcrs hash-algorithm,file] ...] [--verify-bank hash-algorithm] file", "Verify measurement list (experimental).\n"},
>   	{"ima_boot_aggregate", cmd_ima_bootaggr, 0, "[--pcrs hash-algorithm,file] [TPM 1.2 BIOS event log]", "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"},
> @@ -2578,6 +2589,7 @@ static struct option opts[] = {
>   	{"xattr-user", 0, 0, 140},
>   	{"ignore-violations", 0, 0, 141},
>   	{"pcrs", 1, 0, 142},
> +	{"verify-bank", 2, 0, 143},
>   	{}
>   
>   };
> @@ -2766,6 +2778,9 @@ int main(int argc, char *argv[])
>   			}
>   			pcrfile[npcrfile++] = optarg;
>   			break;
> +		case 143:
> +			verify_bank = optarg;
> +			break;
>   		case '?':
>   			exit(1);
>   			break;

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>