On 19/09/2017 13:43, Hao Wu wrote: > REF: https://bugzilla.tianocore.org/show_bug.cgi?id=698 > > Within function NetRandomInitSeed(), left shift a negative value is used > in: > "~Time.Hour << 24" > > which involves undefined behavior. > > Since Time.Hour is of type UINT8 (range from 0 to 23), hence ~Time.Hour > will be a negative value (of type int, signed). > > 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 'Time.Hour' with UINT32 to resolve this issue. > > Cc: Steven Shi <steven....@intel.com> > Cc: Fu Siyuan <siyuan...@intel.com> > Cc: Ye Ting <ting...@intel.com> > Cc: Wu Jiaxin <jiaxin...@intel.com> > Cc: Star Zeng <star.z...@intel.com> > Cc: Eric Dong <eric.d...@intel.com> > Contributed-under: TianoCore Contribution Agreement 1.1 > Signed-off-by: Hao Wu <hao.a...@intel.com> > --- > MdeModulePkg/Library/DxeNetLib/DxeNetLib.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/MdeModulePkg/Library/DxeNetLib/DxeNetLib.c > b/MdeModulePkg/Library/DxeNetLib/DxeNetLib.c > index 7cd7e3aca0..ca5413edcc 100644 > --- a/MdeModulePkg/Library/DxeNetLib/DxeNetLib.c > +++ b/MdeModulePkg/Library/DxeNetLib/DxeNetLib.c > @@ -872,7 +872,7 @@ NetRandomInitSeed ( > UINT64 MonotonicCount; > > gRT->GetTime (&Time, NULL); > - Seed = (~Time.Hour << 24 | Time.Day << 16 | Time.Minute << 8 | > Time.Second); > + Seed = (~(UINT32)Time.Hour << 24 | Time.Day << 16 | Time.Minute << 8 | > Time.Second); > Seed ^= Time.Nanosecond; > Seed ^= Time.Year << 7; Is there any reason why Seed must be XORed with 0xFF000000 (that's what the ~ does)? Would it make sense to either write it explicitly as a XOR, or perhaps the ~ can be removed altogether?
Paolo _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
