[PATCH v2 2/5] 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 accessing the array elements individually.

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>
---

Notes:
    v2:
    
    - replace EFI_COMMON_SECTION_HEADER_UNION with individual array element
      access [Jordan, Phil, Mike]

 MdePkg/Include/Pi/PiFirmwareFile.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/MdePkg/Include/Pi/PiFirmwareFile.h b/MdePkg/Include/Pi/PiFirmwareFile.h
index a9f3bcc4eb8e..05470538de42 100644
--- a/MdePkg/Include/Pi/PiFirmwareFile.h
+++ b/MdePkg/Include/Pi/PiFirmwareFile.h
@@ -480,8 +480,15 @@ typedef struct {
   CHAR16                        VersionString[1];
 } EFI_VERSION_SECTION2;
 
-#define SECTION_SIZE(SectionHeaderPtr) \
-    ((UINT32) (*((UINT32 *) ((EFI_COMMON_SECTION_HEADER *) (UINTN) SectionHeaderPtr)->Size) & 0x00ffffff))
+///
+/// The argument passed as the SectionHeaderPtr parameter to the SECTION_SIZE()
+/// and IS_SECTION2() function-like macros below must not have side effects:
+/// SectionHeaderPtr is evaluated multiple times.
+///
+#define SECTION_SIZE(SectionHeaderPtr) ((UINT32) ( \
+    (((EFI_COMMON_SECTION_HEADER *) (UINTN) (SectionHeaderPtr))->Size[0]      ) | \
+    (((EFI_COMMON_SECTION_HEADER *) (UINTN) (SectionHeaderPtr))->Size[1] <<  8) | \
+    (((EFI_COMMON_SECTION_HEADER *) (UINTN) (SectionHeaderPtr))->Size[2] << 16)))
 
 #define IS_SECTION2(SectionHeaderPtr) \
     (SECTION_SIZE (SectionHeaderPtr) == 0x00ffffff)
-- 
2.19.1.3.g30247aa5d201