[PATCH 02/10] MdePkg/PiFirmwareFile: fix undefined behavior in SECTION_SIZE

["Laszlo Ersek" <lersek@redhat.com>]

RH covscan justifiedly reports that accessing
"EFI_COMMON_SECTION_HEADER.Size", which is of type UINT8[3], through a
(UINT32*), is undefined behavior:

> Error: OVERRUN (CWE-119):
> edk2-89910a39dcfd/OvmfPkg/Sec/SecMain.c:178: overrun-local: Overrunning
> array of 3 bytes at byte offset 3 by dereferencing pointer
> "(UINT32 *)((EFI_COMMON_SECTION_HEADER *)(UINTN)Section)->Size".
> #  176|       Section = (EFI_COMMON_SECTION_HEADER*)(UINTN) CurrentAddress;
> #  177|
> #  178|->     Size = SECTION_SIZE (Section);
> #  179|       if (Size < sizeof (*Section)) {
> #  180|         return EFI_VOLUME_CORRUPTED;

Fix this by introducing EFI_COMMON_SECTION_HEADER_UNION, and expressing
SECTION_SIZE() in terms of "EFI_COMMON_SECTION_HEADER_UNION.Uint32".

Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=1710
Issue: scan-1007.txt
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 MdePkg/Include/Pi/PiFirmwareFile.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/MdePkg/Include/Pi/PiFirmwareFile.h b/MdePkg/Include/Pi/PiFirmwareFile.h
index a9f3bcc4eb8e..4fce8298d1c0 100644
--- a/MdePkg/Include/Pi/PiFirmwareFile.h
+++ b/MdePkg/Include/Pi/PiFirmwareFile.h
@@ -229,16 +229,24 @@ typedef struct {
   ///
   UINT8             Size[3];
   EFI_SECTION_TYPE  Type;
   ///
   /// Declares the section type.
   ///
 } EFI_COMMON_SECTION_HEADER;
 
+///
+/// Union that permits accessing EFI_COMMON_SECTION_HEADER as a UINT32 object.
+///
+typedef union {
+  EFI_COMMON_SECTION_HEADER Hdr;
+  UINT32                    Uint32;
+} EFI_COMMON_SECTION_HEADER_UNION;
+
 typedef struct {
   ///
   /// A 24-bit unsigned integer that contains the total size of the section in bytes,
   /// including the EFI_COMMON_SECTION_HEADER.
   ///
   UINT8             Size[3];
 
   EFI_SECTION_TYPE  Type;
@@ -476,17 +484,17 @@ typedef struct {
   /// A UINT16 that represents a particular build. Subsequent builds have monotonically
   /// increasing build numbers relative to earlier builds.
   ///
   UINT16                        BuildNumber;
   CHAR16                        VersionString[1];
 } EFI_VERSION_SECTION2;
 
 #define SECTION_SIZE(SectionHeaderPtr) \
-    ((UINT32) (*((UINT32 *) ((EFI_COMMON_SECTION_HEADER *) (UINTN) SectionHeaderPtr)->Size) & 0x00ffffff))
+    (((EFI_COMMON_SECTION_HEADER_UNION *) (UINTN) (SectionHeaderPtr))->Uint32 & 0x00ffffff)
 
 #define IS_SECTION2(SectionHeaderPtr) \
     (SECTION_SIZE (SectionHeaderPtr) == 0x00ffffff)
 
 #define SECTION2_SIZE(SectionHeaderPtr) \
     (((EFI_COMMON_SECTION_HEADER2 *) (UINTN) SectionHeaderPtr)->ExtendedSize)
 
 #pragma pack()
-- 
2.19.1.3.g30247aa5d201