From bd42d976d510ab56e862b7bf764b1f9e9b19337e Mon Sep 17 00:00:00 2001 From: Hao Wu Date: Tue, 19 Sep 2017 14:00:45 +0800 Subject: [PATCH] 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 Cc: Qin Long Cc: Star Zeng Cc: Eric Dong Cc: Paolo Bonzini Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Hao Wu Reviewed-by: Wu Jiaxin Reviewed-by: Fu Siyuan Reviewed-by: Ye Ting --- 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; -- 2.39.2