From 568999e62a41d1b8f42c5b945b618099ca999394 Mon Sep 17 00:00:00 2001
From: Remi Lefevre <rlefevre@gmail.com>
Date: Wed, 3 Sep 2008 17:30:44 +0200
Subject: [PATCH] sdi.c32: verify the header checksum

Verify the checksum in the SDI header.

SDIheader variable names and checksum algo are from
http://skolk.livejournal.com/
---
 com32/modules/sdi.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/com32/modules/sdi.c b/com32/modules/sdi.c
index e2be9d5..04e9110 100644
--- a/com32/modules/sdi.c
+++ b/com32/modules/sdi.c
@@ -39,12 +39,25 @@
 # define dprintf(f, ...) ((void)0)
 #endif
 
+typedef uint8_t guid_t[16];
+
 struct SDIHeader {
   uint32_t Signature;
   char     Version[4];
   uint64_t SDIReserved;
   uint64_t BootCodeOffset;
   uint64_t BootCodeSize;
+  uint64_t VendorID;
+  uint64_t DeviceID;
+  guid_t   DeviceModel;
+  uint64_t DeviceRole;
+  uint64_t Reserved1;
+  guid_t   RuntimeGUID;
+  uint64_t RuntimeOEMrev;
+  uint64_t Reserved2;
+  uint64_t PageAlignment;   /* BLOB alignment value in pages */
+  uint64_t Reserved3[48];
+  uint64_t Checksum;
 };
 
 #define SDI_LOAD_ADDR	(16 << 20) /* 16 MB */
@@ -139,6 +152,21 @@ static int boot_sdi(void *ptr, size_t len)
   return -1;
 }
 
+/*
+ * Check that the sum of all bytes from first 512 bytes (SDI header)
+ * is 0 modulo 256.
+ */
+int has_valid_header(unsigned char *header)
+{
+  unsigned char checksum;
+  unsigned int i;
+
+  checksum = 0;
+  for (i = 0; i < sizeof(struct SDIHeader); i++)
+    checksum += header[i];
+  return (!checksum);
+}
+
 int main(int argc, char *argv[])
 {
   void *data;
@@ -160,6 +188,11 @@ int main(int argc, char *argv[])
   }
   fputs("ok\n", stdout);
 
+  if (!has_valid_header(data)) {
+    error("SDI header is corrupted\n");
+    return 1;
+  }
+
   boot_sdi(data, data_len);
   error("Invalid SDI file or insufficient memory\n");
   return 1;
-- 
2.7.4