Looks good to me. Reviewed-by: Fu Siyuan <[email protected]>
-----Original Message----- From: Wu, Hao A Sent: Thursday, September 28, 2017 12:32 PM To: [email protected] Cc: Wu, Hao A <[email protected]>; Shi, Steven <[email protected]>; Fu, Siyuan <[email protected]>; Ye, Ting <[email protected]>; Wu, Jiaxin <[email protected]>; Long, Qin <[email protected]>; Zeng, Star <[email protected]>; Dong, Eric <[email protected]>; Paolo Bonzini <[email protected]> Subject: [PATCH v3 4/5] MdeModulePkg/DxeNetLib: Fix negative value left shift 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 will remove the '~' operator before 'Time.Hour', since it seems like an implementation choice for generating the seed. Cc: Steven Shi <[email protected]> Cc: Fu Siyuan <[email protected]> Cc: Ye Ting <[email protected]> Cc: Wu Jiaxin <[email protected]> Cc: Qin Long <[email protected]> Cc: Star Zeng <[email protected]> Cc: Eric Dong <[email protected]> Cc: Paolo Bonzini <[email protected]> Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Hao Wu <[email protected]> --- 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..1ee77fe036 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 = (Time.Hour << 24 | Time.Day << 16 | Time.Minute << 8 | Time.Second); Seed ^= Time.Nanosecond; Seed ^= Time.Year << 7; -- 2.12.0.windows.1 _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
