Leave the review to module experts.
Thanks,
Star
-----Original Message-----
From: Wu, Hao A
Sent: Thursday, September 21, 2017 2:46 PM
To: edk2-devel@lists.01.org
Cc: Wu, Hao A <hao.a.wu@intel.com>; Shi, Steven <steven.shi@intel.com>; Fu, Siyuan <siyuan.fu@intel.com>; Ye, Ting <ting.ye@intel.com>; Wu, Jiaxin <jiaxin.wu@intel.com>; Long, Qin <qin.long@intel.com>; Zeng, Star <star.zeng@intel.com>; Dong, Eric <eric.dong@intel.com>; Paolo Bonzini <pbonzini@redhat.com>
Subject: [PATCH v2 4/6] 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 <steven.shi@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Ye Ting <ting.ye@intel.com>
Cc: Wu Jiaxin <jiaxin.wu@intel.com>
Cc: Qin Long <qin.long@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@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..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
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