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MdePkg/PrintLib: Fix possible negative value left shift 

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=702

Within function InternalPrintLibSPrintMarker(), possible left shift of a
negative value is found in:
"(*(ArgumentString + 1) << 8)"

which involves undefined behavior.

Since '*(ArgumentString + 1)' is of type CONST CHAR8 (signed), it will be
promoted to type int (signed) during the left shift operation. If
'*(ArgumentString + 1)' is a negative value, the behavior will be
undefined.

According to the C11 spec, Section 6.5.7:
> 4 The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated
>   bits are filled with zeros. If E1 has an unsigned type, the value
>   of the result is E1 * 2^E2 , reduced modulo one more than the
>   maximum value representable in the result type. If E1 has a signed
>   type and nonnegative value, and E1 * 2^E2 is representable in the
>   result type, then that is the resulting value; otherwise, the
>   behavior is undefined.

This commit explicitly cast '*(ArgumentString + 1)' with UINT8 to resolve
this issue.

Cc: Steven Shi <steven.shi@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
This commit is contained in:
Hao Wu 2017-09-19 16:42:04 +08:00
parent 0e6584e386
commit ea0b15067c
1 changed files with 1 additions and 1 deletions
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2
MdePkg/Library/BasePrintLib/PrintLibInternal.c
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@ -1165,7 +1165,7 @@ BasePrintLibSPrintMarker (
// Copy the string into the output buffer performing the required type conversions // Copy the string into the output buffer performing the required type conversions
// //
while (Index < Count) { while (Index < Count) {
ArgumentCharacter = ((*ArgumentString & 0xff) | (*(ArgumentString + 1) << 8)) & ArgumentMask; ArgumentCharacter = ((*ArgumentString & 0xff) | (((UINT8)*(ArgumentString + 1)) << 8)) & ArgumentMask;
LengthToReturn += (1 * BytesPerOutputCharacter); LengthToReturn += (1 * BytesPerOutputCharacter);
if ((Flags & COUNT_ONLY_NO_PRINT) == 0 && Buffer != NULL) { if ((Flags & COUNT_ONLY_NO_PRINT) == 0 && Buffer != NULL) {