[PATCH V4 1/4] tpm: Abstract crypto agile event size calculations

[Matthew Garrett]

From: Matthew Garrett <mjg59 at google.com>

We need to calculate the size of crypto agile events in multiple
locations, including in the EFI boot stub. The easiest way to do this is
to put it in a header file as an inline and leave a wrapper to ensure we
don't end up with multiple copies of it embedded in the existing code.

Signed-off-by: Matthew Garrett <mjg59 at google.com>
---
 drivers/char/tpm/eventlog/tpm2.c | 47 +---------------------
 include/linux/tpm_eventlog.h     | 68 ++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+), 46 deletions(-)

diff --git a/drivers/char/tpm/eventlog/tpm2.c b/drivers/char/tpm/eventlog/tpm2.c
index d8b77133a83a..dc12e1cbd03a 100644
--- a/drivers/char/tpm/eventlog/tpm2.c
+++ b/drivers/char/tpm/eventlog/tpm2.c
@@ -40,52 +40,7 @@
 static int calc_tpm2_event_size(struct tcg_pcr_event2_head *event,
 				struct tcg_pcr_event *event_header)
 {
-	struct tcg_efi_specid_event_head *efispecid;
-	struct tcg_event_field *event_field;
-	void *marker;
-	void *marker_start;
-	u32 halg_size;
-	size_t size;
-	u16 halg;
-	int i;
-	int j;
-
-	marker = event;
-	marker_start = marker;
-	marker = marker + sizeof(event->pcr_idx) + sizeof(event->event_type)
-		+ sizeof(event->count);
-
-	efispecid = (struct tcg_efi_specid_event_head *)event_header->event;
-
-	/* Check if event is malformed. */
-	if (event->count > efispecid->num_algs)
-		return 0;
-
-	for (i = 0; i < event->count; i++) {
-		halg_size = sizeof(event->digests[i].alg_id);
-		memcpy(&halg, marker, halg_size);
-		marker = marker + halg_size;
-		for (j = 0; j < efispecid->num_algs; j++) {
-			if (halg == efispecid->digest_sizes[j].alg_id) {
-				marker +=
-					efispecid->digest_sizes[j].digest_size;
-				break;
-			}
-		}
-		/* Algorithm without known length. Such event is unparseable. */
-		if (j == efispecid->num_algs)
-			return 0;
-	}
-
-	event_field = (struct tcg_event_field *)marker;
-	marker = marker + sizeof(event_field->event_size)
-		+ event_field->event_size;
-	size = marker - marker_start;
-
-	if ((event->event_type == 0) && (event_field->event_size == 0))
-		return 0;
-
-	return size;
+	return __calc_tpm2_event_size(event, event_header);
 }
 
 static void *tpm2_bios_measurements_start(struct seq_file *m, loff_t *pos)
diff --git a/include/linux/tpm_eventlog.h b/include/linux/tpm_eventlog.h
index f47342361e87..09c19d506b69 100644
--- a/include/linux/tpm_eventlog.h
+++ b/include/linux/tpm_eventlog.h
@@ -117,4 +117,72 @@ struct tcg_pcr_event2_head {
 	struct tpm2_digest digests[];
 } __packed;
 
+/**
+ * __calc_tpm2_event_size - calculate the size of a TPM2 event log entry
+ * @event:        Pointer to the event whose size should be calculated
+ * @event_header: Pointer to the initial event containing the digest lengths
+ *
+ * The TPM2 event log format can contain multiple digests corresponding to
+ * separate PCR banks, and also contains a variable length of the data that
+ * was measured. This requires knowledge of how long each digest type is,
+ * and this information is contained within the first event in the log.
+ *
+ * We calculate the length by examining the number of events, and then looking
+ * at each event in turn to determine how much space is used for events in
+ * total. Once we've done this we know the offset of the data length field,
+ * and can calculate the total size of the event.
+ *
+ * Return: size of the event on success, <0 on failure
+ */
+
+static inline int __calc_tpm2_event_size(struct tcg_pcr_event2_head *event,
+					 struct tcg_pcr_event *event_header)
+{
+	struct tcg_efi_specid_event_head *efispecid;
+	struct tcg_event_field *event_field;
+	void *marker;
+	void *marker_start;
+	u32 halg_size;
+	size_t size;
+	u16 halg;
+	int i;
+	int j;
+
+	marker = event;
+	marker_start = marker;
+	marker = marker + sizeof(event->pcr_idx) + sizeof(event->event_type)
+		+ sizeof(event->count);
+
+	efispecid = (struct tcg_efi_specid_event_head *)event_header->event;
+
+	/* Check if event is malformed. */
+	if (event->count > efispecid->num_algs)
+		return 0;
+
+	for (i = 0; i < event->count; i++) {
+		halg_size = sizeof(event->digests[i].alg_id);
+		memcpy(&halg, marker, halg_size);
+		marker = marker + halg_size;
+		for (j = 0; j < efispecid->num_algs; j++) {
+			if (halg == efispecid->digest_sizes[j].alg_id) {
+				marker +=
+					efispecid->digest_sizes[j].digest_size;
+				break;
+			}
+		}
+		/* Algorithm without known length. Such event is unparseable. */
+		if (j == efispecid->num_algs)
+			return 0;
+	}
+
+	event_field = (struct tcg_event_field *)marker;
+	marker = marker + sizeof(event_field->event_size)
+		+ event_field->event_size;
+	size = marker - marker_start;
+
+	if ((event->event_type == 0) && (event_field->event_size == 0))
+		return 0;
+
+	return size;
+}
 #endif
-- 
2.21.0.rc0.258.g878e2cd30e-goog