[PATCH v2] ima: optimize ima_pcr_extend function by asynchronous

[Tianjia Zhang]

Because ima_pcr_extend() to operate the TPM chip, this process is
very time-consuming, for IMA, this is a blocking action, especially
when the TPM is in self test state, this process will block for up
to second level.

Because the return result of ima_pcr_extend() is of no concern to IMA,
it only affects the audit of IMA, so this patch use async_schedule()
and PCR extend event serial queue to asynchronously perform the
ima_pcr_extend() operation and do an audit operation at the end.

In a vtpm scenario, I added the measure policy of BPRM and MMAP to
compare the efficiency before and after applying the patch. The results
show that the overall startup efficiency of conventional processes can
be increased by 5% to 10%. I believe this efficiency increase It will
be more obvious on real hardware tpm.

Signed-off-by: Tianjia Zhang <tianjia.zhang at linux.alibaba.com>
---

v2 chang:
  Use a queue to queue tpm extend operations to avoid out of order

 security/integrity/ima/ima_queue.c | 102 +++++++++++++++++++++++------
 1 file changed, 81 insertions(+), 21 deletions(-)

diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
index edbc2d6962be..ec146270d94b 100644
--- a/security/integrity/ima/ima_queue.c
+++ b/security/integrity/ima/ima_queue.c
@@ -17,6 +17,7 @@
 
 #include <linux/rculist.h>
 #include <linux/slab.h>
+#include <linux/async.h>
 #include "ima.h"
 
 #define AUDIT_CAUSE_LEN_MAX 32
@@ -44,6 +45,21 @@ struct ima_h_table ima_htable = {
  */
 static DEFINE_MUTEX(ima_extend_list_mutex);
 
+/* list for pcr extned asynchronous */
+static LIST_HEAD(ima_pcr_extend_list);
+
+struct ima_pcr_extend_async_ctx {
+	struct list_head list;
+	struct ima_template_entry *entry;
+	int violation;
+	const char *op;
+	struct inode *inode;
+	const unsigned char *filename;
+	const char *audit_cause;
+	int audit_info;
+	int result;
+};
+
 /* 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)
@@ -150,6 +166,48 @@ static int ima_pcr_extend(const u8 *hash, int pcr)
 	return result;
 }
 
+static void ima_pcr_extend_async(void *data, async_cookie_t cookie)
+{
+	struct ima_pcr_extend_async_ctx *ctx;
+	u8 digest[TPM_DIGEST_SIZE];
+	char tpm_audit_cause[AUDIT_CAUSE_LEN_MAX];
+	int empty;
+	int result;
+
+retry:
+	mutex_lock(&ima_extend_list_mutex);
+	empty = list_empty(&ima_pcr_extend_list);
+	if (!empty) {
+		ctx = list_first_entry(&ima_pcr_extend_list,
+				struct ima_pcr_extend_async_ctx, list);
+		list_del(&ctx->list);
+	}
+	mutex_unlock(&ima_extend_list_mutex);
+
+	/* no more pending pcr_extend, return */
+	if (empty)
+		return;
+
+	if (ctx->violation)		/* invalidate pcr */
+		memset(digest, 0xff, sizeof(digest));
+	else
+		memcpy(digest, ctx->entry->digest, sizeof(digest));
+
+	result = ima_pcr_extend(digest, ctx->entry->pcr);
+	if (result != 0) {
+		snprintf(tpm_audit_cause, AUDIT_CAUSE_LEN_MAX, "TPM_error(%d)",
+			 result);
+		ctx->audit_cause = tpm_audit_cause;
+		ctx->audit_info = 0;
+	}
+	integrity_audit_msg(AUDIT_INTEGRITY_PCR, ctx->inode, ctx->filename,
+			    ctx->op, ctx->audit_cause,
+			    ctx->result, ctx->audit_info);
+
+	kfree(ctx);
+	goto retry;
+}
+
 /*
  * Add template entry to the measurement list and hash table, and
  * extend the pcr.
@@ -162,20 +220,16 @@ int ima_add_template_entry(struct ima_template_entry *entry, int violation,
 			   const char *op, struct inode *inode,
 			   const unsigned char *filename)
 {
-	u8 digest[TPM_DIGEST_SIZE];
 	const char *audit_cause = "hash_added";
-	char tpm_audit_cause[AUDIT_CAUSE_LEN_MAX];
 	int audit_info = 1;
-	int result = 0, tpmresult = 0;
+	int result = 0;
+	struct ima_pcr_extend_async_ctx *ctx;
 
 	mutex_lock(&ima_extend_list_mutex);
-	if (!violation) {
-		memcpy(digest, entry->digest, sizeof(digest));
-		if (ima_lookup_digest_entry(digest, entry->pcr)) {
-			audit_cause = "hash_exists";
-			result = -EEXIST;
-			goto out;
-		}
+	if (!violation && ima_lookup_digest_entry(entry->digest, entry->pcr)) {
+		audit_cause = "hash_exists";
+		result = -EEXIST;
+		goto out;
 	}
 
 	result = ima_add_digest_entry(entry, 1);
@@ -185,20 +239,26 @@ int ima_add_template_entry(struct ima_template_entry *entry, int violation,
 		goto out;
 	}
 
-	if (violation)		/* invalidate pcr */
-		memset(digest, 0xff, sizeof(digest));
-
-	tpmresult = ima_pcr_extend(digest, entry->pcr);
-	if (tpmresult != 0) {
-		snprintf(tpm_audit_cause, AUDIT_CAUSE_LEN_MAX, "TPM_error(%d)",
-			 tpmresult);
-		audit_cause = tpm_audit_cause;
-		audit_info = 0;
+	ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
+	if (!ctx) {
+		audit_cause = "ENOMEM";
+		result = -ENOMEM;
+		goto out;
 	}
+
+	ctx->entry = entry;
+	ctx->violation = violation;
+	ctx->op = op;
+	ctx->inode = inode;
+	ctx->filename = filename;
+	ctx->audit_cause = audit_cause;
+	ctx->audit_info = audit_info;
+	ctx->result = result;
+	list_add_tail(&ctx->list, &ima_pcr_extend_list);
+	async_schedule(ima_pcr_extend_async, NULL);
+
 out:
 	mutex_unlock(&ima_extend_list_mutex);
-	integrity_audit_msg(AUDIT_INTEGRITY_PCR, inode, filename,
-			    op, audit_cause, result, audit_info);
 	return result;
 }
 
-- 
2.17.1