From 213da0b540891ba614753673ce3ed54940434497 Mon Sep 17 00:00:00 2001
From: Hao Wu <hao.a.wu@intel.com>
Date: Mon, 22 May 2017 15:03:24 +0800
Subject: [PATCH] MdeModulePkg/PrintLib: Avoid reading content beyond the
 format string

https://bugzilla.tianocore.org/show_bug.cgi?id=567

In functions DxePrintLibPrint2ProtocolVaListToBaseList() and
InternalPrintLibSPrintMarker(), when processing ASCII format strings, if
the format string walker pointer 'Format' is pointing at the end of the
format string (i.e. '\0'), the following expression:
*(Format + 1)
will read an undefined value.

Though this value won't affect the functionality, since it will be masked
by variable 'FormatMask':
(*(Format + 1) << 8)) & FormatMask
(FormatMask is 0xff for ASCII format string)

This commit adds additional logic to avoid reading undefined content.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
---
 .../DxePrintLibPrint2Protocol/PrintLib.c      | 22 +++++++++----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/MdeModulePkg/Library/DxePrintLibPrint2Protocol/PrintLib.c b/MdeModulePkg/Library/DxePrintLibPrint2Protocol/PrintLib.c
index 9f702c4fef..b58db8e011 100644
--- a/MdeModulePkg/Library/DxePrintLibPrint2Protocol/PrintLib.c
+++ b/MdeModulePkg/Library/DxePrintLibPrint2Protocol/PrintLib.c
@@ -130,7 +130,7 @@ DxePrintLibPrint2ProtocolVaListToBaseList (
   //
   // Get the first character from the format string
   //
-  FormatCharacter = ((*Format & 0xff) | (*(Format + 1) << 8)) & FormatMask;
+  FormatCharacter = ((*Format & 0xff) | ((BytesPerFormatCharacter == 1) ? 0 : (*(Format + 1) << 8))) & FormatMask;
 
   while (FormatCharacter != 0) {
     if (FormatCharacter == '%') {
@@ -148,7 +148,7 @@ DxePrintLibPrint2ProtocolVaListToBaseList (
         //
         // Get the next character from the format string
         //
-        FormatCharacter = ((*Format & 0xff) | (*(Format + 1) << 8)) & FormatMask;
+        FormatCharacter = ((*Format & 0xff) | ((BytesPerFormatCharacter == 1) ? 0 : (*(Format + 1) << 8))) & FormatMask;
 
         switch (FormatCharacter) {
         case '.': 
@@ -239,7 +239,7 @@ DxePrintLibPrint2ProtocolVaListToBaseList (
     //
     // Get the next character from the format string
     //
-    FormatCharacter = ((*Format & 0xff) | (*(Format + 1) << 8)) & FormatMask;
+    FormatCharacter = ((*Format & 0xff) | ((BytesPerFormatCharacter == 1) ? 0 : (*(Format + 1) << 8))) & FormatMask;
   }
   return TRUE;
 }
@@ -1596,7 +1596,7 @@ InternalPrintLibSPrintMarker (
   //
   // Get the first character from the format string
   //
-  FormatCharacter = ((*Format & 0xff) | (*(Format + 1) << 8)) & FormatMask;
+  FormatCharacter = ((*Format & 0xff) | ((BytesPerFormatCharacter == 1) ? 0 : (*(Format + 1) << 8))) & FormatMask;
 
   //
   // Loop until the end of the format string is reached or the output buffer is full
@@ -1628,7 +1628,7 @@ InternalPrintLibSPrintMarker (
       //
       for (Done = FALSE; !Done; ) {
         Format += BytesPerFormatCharacter;
-        FormatCharacter = ((*Format & 0xff) | (*(Format + 1) << 8)) & FormatMask;
+        FormatCharacter = ((*Format & 0xff) | ((BytesPerFormatCharacter == 1) ? 0 : (*(Format + 1) << 8))) & FormatMask;
         switch (FormatCharacter) {
         case '.': 
           Flags |= PRECISION; 
@@ -1681,7 +1681,7 @@ InternalPrintLibSPrintMarker (
           for (Count = 0; ((FormatCharacter >= '0') &&  (FormatCharacter <= '9')); ){
             Count = (Count * 10) + FormatCharacter - '0';
             Format += BytesPerFormatCharacter;
-            FormatCharacter = ((*Format & 0xff) | (*(Format + 1) << 8)) & FormatMask;
+            FormatCharacter = ((*Format & 0xff) | ((BytesPerFormatCharacter == 1) ? 0 : (*(Format + 1) << 8))) & FormatMask;
           }
           Format -= BytesPerFormatCharacter;
           if ((Flags & PRECISION) == 0) {
@@ -1960,7 +1960,7 @@ InternalPrintLibSPrintMarker (
 
       case '\r':
         Format += BytesPerFormatCharacter;
-        FormatCharacter = ((*Format & 0xff) | (*(Format + 1) << 8)) & FormatMask;
+        FormatCharacter = ((*Format & 0xff) | ((BytesPerFormatCharacter == 1) ? 0 : (*(Format + 1) << 8))) & FormatMask;
         if (FormatCharacter == '\n') {
           //
           // Translate '\r\n' to '\r\n'
@@ -1981,7 +1981,7 @@ InternalPrintLibSPrintMarker (
         //
         ArgumentString = "\r\n";
         Format += BytesPerFormatCharacter;
-        FormatCharacter = ((*Format & 0xff) | (*(Format + 1) << 8)) & FormatMask;
+        FormatCharacter = ((*Format & 0xff) | ((BytesPerFormatCharacter == 1) ? 0 : (*(Format + 1) << 8))) & FormatMask;
         if (FormatCharacter != '\r') {
           Format   -= BytesPerFormatCharacter;
         }
@@ -2000,7 +2000,7 @@ InternalPrintLibSPrintMarker (
  
     case '\r':
       Format += BytesPerFormatCharacter;
-      FormatCharacter = ((*Format & 0xff) | (*(Format + 1) << 8)) & FormatMask;
+      FormatCharacter = ((*Format & 0xff) | ((BytesPerFormatCharacter == 1) ? 0 : (*(Format + 1) << 8))) & FormatMask;
       if (FormatCharacter == '\n') {
         //
         // Translate '\r\n' to '\r\n'
@@ -2021,7 +2021,7 @@ InternalPrintLibSPrintMarker (
       //
       ArgumentString = "\r\n";
       Format += BytesPerFormatCharacter;
-      FormatCharacter = ((*Format & 0xff) | (*(Format + 1) << 8)) & FormatMask;
+      FormatCharacter = ((*Format & 0xff) | ((BytesPerFormatCharacter == 1) ? 0 : (*(Format + 1) << 8))) & FormatMask;
       if (FormatCharacter != '\r') {
         Format   -= BytesPerFormatCharacter;
       }
@@ -2149,7 +2149,7 @@ InternalPrintLibSPrintMarker (
     //
     // Get the next character from the format string
     //
-    FormatCharacter = ((*Format & 0xff) | (*(Format + 1) << 8)) & FormatMask;
+    FormatCharacter = ((*Format & 0xff) | ((BytesPerFormatCharacter == 1) ? 0 : (*(Format + 1) << 8))) & FormatMask;
   }
 
   if ((Flags & COUNT_ONLY_NO_PRINT) != 0) {
-- 
2.39.2