shim: Ignore UEFI LoadOptions that are just NUL characters.

I don't know when or why we ever see this, but it's easy enough to
avoid.

Resolves github issue #95

Signed-off-by: Peter Jones <pjones@redhat.com>

2 files changed, 26 insertions, 0 deletions

diff --git a/shim.c b/shim.c
index 818eff39..34b819a9 100644
--- a/shim.c
+++ b/shim.c
@@ -2583,6 +2583,12 @@ EFI_STATUS set_second_stage (EFI_HANDLE image_handle)
 	}
 
 	/*
+	 * Apparently sometimes we get L"\0\0"?  Which isn't useful at all.
+	 */
+	if (is_all_nuls(li->LoadOptions, li->LoadOptionsSize))
+		return EFI_SUCCESS;
+
+	/*
 	 * Check and see if this is just a list of strings.  If it's an
 	 * EFI_LOAD_OPTION, it'll be 0, since we know EndEntire device path
 	 * won't pass muster as UCS2-LE.
diff --git a/ucs2.h b/ucs2.h
index 010d0966..806774c7 100644
--- a/ucs2.h
+++ b/ucs2.h
@@ -36,6 +36,8 @@
 #ifndef SHIM_UCS2_H
 #define SHIM_UCS2_H
 
+#include <stdbool.h>
+
 static inline INTN
 __attribute__((unused))
 StrCaseCmp(CHAR16 *s0, CHAR16 *s1)
@@ -89,6 +91,24 @@ StrCSpn(const CHAR16 *s, const CHAR16 *reject)
 	return ret;
 }
 
+/*
+ * Test if an entire buffer is nothing but NUL characters.  This
+ * implementation "gracefully" ignores the difference between the
+ * UTF-8/ASCII 1-byte NUL and the UCS-2 2-byte NUL.
+ */
+static inline bool
+__attribute__((__unused__))
+is_all_nuls(UINT8 *data, UINTN data_size)
+{
+	UINTN i;
+
+	for (i = 0; i < data_size; i++) {
+		if (data[i] != 0)
+			return false;
+	}
+	return true;
+}
+
 static inline UINTN
 __attribute__((__unused__))
 count_ucs2_strings(UINT8 *data, UINTN data_size)