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LowerBitSets: Avoid reusing byte set addresses. 

Each use of the byte array uses a different alias. This makes the
backend less likely to reuse previously computed byte array addresses,
improving the security of the CFI mechanism based on this pass.

Differential Revision: http://reviews.llvm.org/D8455

llvm-svn: 232770
This commit is contained in:
Peter Collingbourne 2015-03-19 22:02:10 +00:00
parent 070843d60b
commit 994ba3d29c
2 changed files with 24 additions and 5 deletions
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17
llvm/lib/Transforms/IPO/LowerBitSets.cpp
View File

@ -38,6 +38,11 @@ STATISTIC(NumByteArraysCreated, "Number of byte arrays created");
STATISTIC(NumBitSetCallsLowered, "Number of bitset calls lowered"); STATISTIC(NumBitSetCallsLowered, "Number of bitset calls lowered");
STATISTIC(NumBitSetDisjointSets, "Number of disjoint sets of bitsets"); STATISTIC(NumBitSetDisjointSets, "Number of disjoint sets of bitsets");
static cl::opt<bool> AvoidReuse(
"lowerbitsets-avoid-reuse",
cl::desc("Try to avoid reuse of byte array addresses using aliases"),
cl::Hidden, cl::init(true));
bool BitSetInfo::containsGlobalOffset(uint64_t Offset) const { bool BitSetInfo::containsGlobalOffset(uint64_t Offset) const {
if (Offset < ByteOffset) if (Offset < ByteOffset)
return false; return false;
@ -389,7 +394,17 @@ Value *LowerBitSets::createBitSetTest(IRBuilder<> &B, BitSetInfo &BSI,
BAI = createByteArray(BSI); BAI = createByteArray(BSI);
} }
Value *ByteAddr = B.CreateGEP(BAI->ByteArray, BitOffset); Constant *ByteArray = BAI->ByteArray;
if (!LinkerSubsectionsViaSymbols && AvoidReuse) {
// Each use of the byte array uses a different alias. This makes the
// backend less likely to reuse previously computed byte array addresses,
// improving the security of the CFI mechanism based on this pass.
ByteArray = GlobalAlias::create(
BAI->ByteArray->getType()->getElementType(), 0,
GlobalValue::PrivateLinkage, "bits_use", ByteArray, M);
}
Value *ByteAddr = B.CreateGEP(ByteArray, BitOffset);
Value *Byte = B.CreateLoad(ByteAddr); Value *Byte = B.CreateLoad(ByteAddr);
Value *ByteAndMask = B.CreateAnd(Byte, BAI->Mask); Value *ByteAndMask = B.CreateAnd(Byte, BAI->Mask);

12
llvm/test/Transforms/LowerBitSets/simple.ll
View File

@ -38,6 +38,10 @@ target datalayout = "e-p:32:32"
!llvm.bitsets = !{ !0, !1, !2, !3, !4, !5, !6, !7 } !llvm.bitsets = !{ !0, !1, !2, !3, !4, !5, !6, !7 }
; CHECK: @bits_use{{[0-9]*}} = private alias i8* @bits{{[0-9]*}}
; CHECK: @bits_use{{[0-9]*}} = private alias i8* @bits{{[0-9]*}}
; CHECK: @bits_use{{[0-9]*}} = private alias i8* @bits{{[0-9]*}}
; CHECK: @a = alias getelementptr inbounds ({ i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }, { i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }* [[G]], i32 0, i32 0) ; CHECK: @a = alias getelementptr inbounds ({ i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }, { i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }* [[G]], i32 0, i32 0)
; CHECK: @b = alias getelementptr inbounds ({ i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }, { i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }* [[G]], i32 0, i32 2) ; CHECK: @b = alias getelementptr inbounds ({ i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }, { i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }* [[G]], i32 0, i32 2)
; CHECK: @c = alias getelementptr inbounds ({ i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }, { i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }* [[G]], i32 0, i32 4) ; CHECK: @c = alias getelementptr inbounds ({ i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }, { i32, [0 x i8], [63 x i32], [4 x i8], i32, [0 x i8], [2 x i32] }* [[G]], i32 0, i32 4)
@ -57,8 +61,8 @@ target datalayout = "e-p:32:32"
; CHECK-DARWIN: [[G]] = private constant ; CHECK-DARWIN: [[G]] = private constant
; CHECK: @bits = private alias getelementptr inbounds ([68 x i8], [68 x i8]* [[BA]], i32 0, i32 0) ; CHECK: @bits{{[0-9]*}} = private alias getelementptr inbounds ([68 x i8], [68 x i8]* [[BA]], i32 0, i32 0)
; CHECK: @bits1 = private alias getelementptr inbounds ([68 x i8], [68 x i8]* [[BA]], i32 0, i32 0) ; CHECK: @bits{{[0-9]*}} = private alias getelementptr inbounds ([68 x i8], [68 x i8]* [[BA]], i32 0, i32 0)
declare i1 @llvm.bitset.test(i8* %ptr, metadata %bitset) nounwind readnone declare i1 @llvm.bitset.test(i8* %ptr, metadata %bitset) nounwind readnone
@ -76,7 +80,7 @@ define i1 @foo(i32* %p) {
; CHECK: [[R6:%[^ ]*]] = icmp ult i32 [[R5]], 68 ; CHECK: [[R6:%[^ ]*]] = icmp ult i32 [[R5]], 68
; CHECK: br i1 [[R6]] ; CHECK: br i1 [[R6]]
; CHECK: [[R8:%[^ ]*]] = getelementptr i8, i8* @bits, i32 [[R5]] ; CHECK: [[R8:%[^ ]*]] = getelementptr i8, i8* @bits_use{{[0-9]*}}, i32 [[R5]]
; CHECK: [[R9:%[^ ]*]] = load i8, i8* [[R8]] ; CHECK: [[R9:%[^ ]*]] = load i8, i8* [[R8]]
; CHECK: [[R10:%[^ ]*]] = and i8 [[R9]], 1 ; CHECK: [[R10:%[^ ]*]] = and i8 [[R9]], 1
; CHECK: [[R11:%[^ ]*]] = icmp ne i8 [[R10]], 0 ; CHECK: [[R11:%[^ ]*]] = icmp ne i8 [[R10]], 0
@ -119,7 +123,7 @@ define i1 @baz(i32* %p) {
; CHECK: [[T6:%[^ ]*]] = icmp ult i32 [[T5]], 66 ; CHECK: [[T6:%[^ ]*]] = icmp ult i32 [[T5]], 66
; CHECK: br i1 [[T6]] ; CHECK: br i1 [[T6]]
; CHECK: [[T8:%[^ ]*]] = getelementptr i8, i8* @bits1, i32 [[T5]] ; CHECK: [[T8:%[^ ]*]] = getelementptr i8, i8* @bits_use{{[0-9]*}}, i32 [[T5]]
; CHECK: [[T9:%[^ ]*]] = load i8, i8* [[T8]] ; CHECK: [[T9:%[^ ]*]] = load i8, i8* [[T8]]
; CHECK: [[T10:%[^ ]*]] = and i8 [[T9]], 2 ; CHECK: [[T10:%[^ ]*]] = and i8 [[T9]], 2
; CHECK: [[T11:%[^ ]*]] = icmp ne i8 [[T10]], 0 ; CHECK: [[T11:%[^ ]*]] = icmp ne i8 [[T10]], 0