linux-kernel - [PATCH] extend IMA boot_aggregate with kernel measurements

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Message-Id: <20200618201126.2081-1-maurizio.drocco@ibm.com>
Date:   Thu, 18 Jun 2020 16:11:25 -0400
From:   Maurizio Drocco <maurizio.drocco@....com>
To:     roberto.sassu@...wei.com
Cc:     Silviu.Vlasceanu@...wei.com, dmitry.kasatkin@...il.com,
        jejb@...ux.ibm.com, jmorris@...ei.org,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, maurizio.drocco@....com,
        serge@...lyn.com, zohar@...ux.ibm.com, mdrocco@...ux.vnet.ibm.com
Subject: [PATCH] extend IMA boot_aggregate with kernel measurements

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 <maurizio.drocco@....com>
---
 security/integrity/ima/ima.h        |  2 +-
 security/integrity/ima/ima_crypto.c | 20 ++++++++++++++++++--
 2 files changed, 19 insertions(+), 3 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..299b23dad8d9 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);
@@ -823,13 +823,29 @@ static int ima_calc_boot_aggregate_tfm(char *digest, u16 alg_id,
 	if (rc != 0)
 		return rc;
 
-	/* cumulative sha1 over tpm registers 0-7 */
+	/* cumulative digest over tpm registers 0-7 */
 	for (i = TPM_PCR0; i < TPM_PCR8; i++) {
 		ima_pcrread(i, &d);
 		/* now accumulate with current aggregate */
 		rc = crypto_shash_update(shash, d.digest,
 					 crypto_shash_digestsize(tfm));
 	}
+	/*
+	 * extend cumulative digest over tpm registers 8-9, which contain
+	 * measurement for the kernel command line (reg. 8) and image (reg. 9)
+	 * in a typical PCR allocation. Registers 8-9 are only included in
+	 * non-SHA1 boot_aggregate digests to avoid ambiguity.
+	 */
+	if (alg_id != TPM_ALG_SHA1) {
+		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