[PATCH] extend IMA boot_aggregate with kernel measurements
From: Maurizio Drocco <hidden>
Date: 2020-06-12 14:38:46
Also in:
linux-integrity, lkml
Subsystem:
extended verification module (evm), integrity measurement architecture (ima), security subsystem, the rest · Maintainers:
Mimi Zohar, Roberto Sassu, Dmitry Kasatkin, Paul Moore, James Morris, "Serge E. Hallyn", Linus Torvalds
IMA is not considering TPM registers 8-9 when calculating the boot aggregate. When registers 8-9 are used to store measurements of the kernel and its command line (e.g., grub2 bootloader with tpm module enabled), IMA should include them in the boot aggregate. Signed-off-by: Maurizio Drocco <redacted> --- security/integrity/ima/ima.h | 2 +- security/integrity/ima/ima_crypto.c | 15 ++++++++++++++- 2 files changed, 15 insertions(+), 2 deletions(-)
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index df93ac258e01..9d94080bdad8 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h@@ -30,7 +30,7 @@ enum ima_show_type { IMA_SHOW_BINARY, IMA_SHOW_BINARY_NO_FIELD_LEN, IMA_SHOW_BINARY_OLD_STRING_FMT, IMA_SHOW_ASCII }; -enum tpm_pcrs { TPM_PCR0 = 0, TPM_PCR8 = 8 }; +enum tpm_pcrs { TPM_PCR0 = 0, TPM_PCR8 = 8, TPM_PCR10 = 10 }; /* digest size for IMA, fits SHA1 or MD5 */ #define IMA_DIGEST_SIZE SHA1_DIGEST_SIZE
diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
index 220b14920c37..64f5e3151e18 100644
--- a/security/integrity/ima/ima_crypto.c
+++ b/security/integrity/ima/ima_crypto.c@@ -809,7 +809,7 @@ static void ima_pcrread(u32 idx, struct tpm_digest *d) static int ima_calc_boot_aggregate_tfm(char *digest, u16 alg_id, struct crypto_shash *tfm) { - struct tpm_digest d = { .alg_id = alg_id, .digest = {0} }; + struct tpm_digest d = { .alg_id = alg_id, .digest = {0} }, d0 = d; int rc; u32 i; SHASH_DESC_ON_STACK(shash, tfm);
@@ -830,6 +830,19 @@ static int ima_calc_boot_aggregate_tfm(char *digest, u16 alg_id, rc = crypto_shash_update(shash, d.digest, crypto_shash_digestsize(tfm)); } + /* + * extend cumulative sha1 over tpm registers 8-9, which contain + * measurement for the kernel command line (reg. 8) and image (reg. 9) + * in a typical PCR allocation. + */ + for (i = TPM_PCR8; i < TPM_PCR10; i++) { + ima_pcrread(i, &d); + /* if not zero, accumulate with current aggregate */ + if (memcmp(d.digest, d0.digest, + crypto_shash_digestsize(tfm)) != 0) + rc = crypto_shash_update(shash, d.digest, + crypto_shash_digestsize(tfm)); + } if (!rc) crypto_shash_final(shash, digest); return rc;
--
2.17.1