IntelFrameworkModulePkg/IdeBusDxe: Fix undefined behavior in signed left shift

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>

0 files changed, 0 insertions, 0 deletions