[RFC,v1,4/7] ima: track the set of PCRs ever extended

Commit Message

Nicolai Stange March 13, 2025, 5:33 p.m. UTC

A subsequent patch will make IMA to invalidate PCR banks associated with
unsupported hash algorithms once at a PCR's first use. To prepare for
that, make it track the set of PCRs ever extended.

Maintain the set of touched PCRs in an unsigned long bitmask,
'ima_extended_pcrs_mask'.

Amend the IMA_INVALID_PCR() #define to check that a given PCR can get
represented in that bitmask. Note that this is only for improving code
maintainablity, it does not actually constain the set of allowed PCR
indices any further.

Make ima_pcr_extend() to maintain the ima_extended_pcrs_mask, i.e.
to set the currently extented PCR's corresponding bit.

Make ima_restore_measurement_list() to restore the ima_extended_pcrs_mask
from the measurement list in order to maintain it across kexecs.

Signed-off-by: Nicolai Stange <[e-mail]>
---
 security/integrity/ima/ima.h          | 8 ++++++--
 security/integrity/ima/ima_queue.c    | 6 ++++++
 security/integrity/ima/ima_template.c | 7 +++++++
 3 files changed, 19 insertions(+), 2 deletions(-)

Patch

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 1158a7b8bf6b..f99b1f81b35c 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -20,6 +20,7 @@ 
 #include <linux/hash.h>
 #include <linux/tpm.h>
 #include <linux/audit.h>
+#include <linux/minmax.h>
 #include <crypto/hash_info.h>
 
 #include "../integrity.h"
@@ -62,6 +63,8 @@  extern int ima_hash_algo_idx __ro_after_init;
 extern int ima_extra_slots __ro_after_init;
 extern struct ima_algo_desc *ima_algo_array __ro_after_init;
 
+extern unsigned long ima_extended_pcrs_mask;
+
 extern int ima_appraise;
 extern struct tpm_chip *ima_tpm_chip;
 extern const char boot_aggregate_name[];
@@ -198,8 +201,9 @@  struct ima_iint_cache {
 	struct ima_digest_data *ima_hash;
 };
 
-#define IMA_INVALID_PCR(a) (((a) < 0) || \
-	(a) >= (sizeof_field(struct ima_iint_cache, measured_pcrs) * 8))
+#define IMA_INVALID_PCR(a) (((a) < 0) ||				    \
+	(a) >= (8 * min(sizeof_field(struct ima_iint_cache, measured_pcrs), \
+			sizeof(ima_extended_pcrs_mask))))
 
 
 extern struct lsm_blob_sizes ima_blob_sizes;
diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index 83d53824aa98..f00ba2222c34 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -51,6 +51,11 @@  static DEFINE_MUTEX(ima_extend_list_mutex);
  */
 static bool ima_measurements_suspended;
 
+/*
+ * Set of PCRs ever extended by IMA.
+ */
+unsigned long ima_extended_pcrs_mask;
+
 /* lookup up the digest value in the hash table, and return the entry */
 static struct ima_queue_entry *ima_lookup_digest_entry(u8 *digest_value,
 						       int pcr)
@@ -152,6 +157,7 @@  static int ima_pcr_extend(struct tpm_digest *digests_arg, int pcr)
 	result = tpm_pcr_extend(ima_tpm_chip, pcr, digests_arg);
 	if (result != 0)
 		pr_err("Error Communicating to TPM chip, result: %d\n", result);
+	ima_extended_pcrs_mask |= BIT(pcr);
 	return result;
 }
 
diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
index 04c49f05cb74..55d335097d85 100644
--- a/security/integrity/ima/ima_template.c
+++ b/security/integrity/ima/ima_template.c
@@ -525,12 +525,19 @@  int ima_restore_measurement_list(loff_t size, void *buf)
 			}
 		}
 
+		if (IMA_INVALID_PCR(entry->pcr)) {
+			pr_err("invalid measurement PCR index");
+			ret = -EINVAL;
+			break;
+		}
+
 		entry->pcr = !ima_canonical_fmt ? *(u32 *)(hdr[HDR_PCR].data) :
 			     le32_to_cpu(*(__le32 *)(hdr[HDR_PCR].data));
 		ret = ima_restore_measurement_entry(entry);
 		if (ret < 0)
 			break;
 
+		ima_extended_pcrs_mask |= BIT(entry->pcr);
 	}
 	return ret;
 }