1 files changed, 24 insertions, 5 deletions

diff --git a/include/linux/tpm_eventlog.h b/include/linux/tpm_eventlog.h
index 4f8c90c93c29..891368e82558 100644
--- a/include/linux/tpm_eventlog.h
+++ b/include/linux/tpm_eventlog.h
@@ -81,6 +81,8 @@ struct tcg_efi_specid_event_algs {
 	u16 digest_size;
 } __packed;
 
+#define TCG_SPECID_SIG "Spec ID Event03"
+
 struct tcg_efi_specid_event_head {
 	u8 signature[16];
 	u32 platform_class;
@@ -155,7 +157,7 @@ struct tcg_algorithm_info {
  * Return: size of the event on success, 0 on failure
  */
 
-static inline int __calc_tpm2_event_size(struct tcg_pcr_event2_head *event,
+static __always_inline u32 __calc_tpm2_event_size(struct tcg_pcr_event2_head *event,
 					 struct tcg_pcr_event *event_header,
 					 bool do_mapping)
 {
@@ -171,6 +173,7 @@ static inline int __calc_tpm2_event_size(struct tcg_pcr_event2_head *event,
 	int i;
 	int j;
 	u32 count, event_type;
+	const u8 zero_digest[sizeof(event_header->digest)] = {0};
 
 	marker = event;
 	marker_start = marker;
@@ -195,13 +198,29 @@ static inline int __calc_tpm2_event_size(struct tcg_pcr_event2_head *event,
 	 * The loop below will unmap these fields if the log is larger than
 	 * one page, so save them here for reference:
 	 */
-	count = READ_ONCE(event->count);
-	event_type = READ_ONCE(event->event_type);
+	count = event->count;
+	event_type = event->event_type;
+
+	/* Verify that it's the log header */
+	if (event_header->pcr_idx != 0 ||
+	    event_header->event_type != NO_ACTION ||
+	    memcmp(event_header->digest, zero_digest, sizeof(zero_digest))) {
+		size = 0;
+		goto out;
+	}
 
 	efispecid = (struct tcg_efi_specid_event_head *)event_header->event;
 
-	/* Check if event is malformed. */
-	if (count > efispecid->num_algs) {
+	/*
+	 * Perform validation of the event in order to identify malformed
+	 * events. This function may be asked to parse arbitrary byte sequences
+	 * immediately following a valid event log. The caller expects this
+	 * function to recognize that the byte sequence is not a valid event
+	 * and to return an event size of 0.
+	 */
+	if (memcmp(efispecid->signature, TCG_SPECID_SIG,
+		   sizeof(TCG_SPECID_SIG)) ||
+	    !efispecid->num_algs || count != efispecid->num_algs) {
 		size = 0;
 		goto out;
 	}