In function AtapiReadCapacity(), the following expression:
IdeDev->BlkIo.Media->LastBlock = (Data.LastLba3 << 24) |
(Data.LastLba2 << 16) |
(Data.LastLba1 << 8) |
Data.LastLba0;
(There is also a similar case in this function.)
will involve undefined behavior in signed left shift operations.
Since Data.LastLbaX is of type UINT8, and
IdeDev->BlkIo.Media->LastBlock is of type UINT64. Therefore,
Data.LastLbaX will be promoted to int (32 bits, signed) first,
and then perform the left shift operation.
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.
So if bit 7 of Data.LastLba3 is 1, (Data.LastLba3 << 24) will be out of
the range within int type. The undefined behavior of the signed left shift
will lead to a potential of setting the high 32 bits of
IdeDev->BlkIo.Media->LastBlock to 1 during the cast from type int to type
UINT64.
This commit will add an explicit UINT32 type cast for Data.LastLba3 to
resolve this issue.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
Hao Wu
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