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Re-apply "[ubsan] Sanity-check shift amounts before truncation" 

This re-applies r293343 (reverts commit r293475) with a fix for an
assertion failure caused by a missing integer cast. I tested this patch
by using the built compiler to compile X86FastISel.cpp.o with ubsan.

Original commit message:

Ubsan does not report UB shifts in some cases where the shift exponent
needs to be truncated to match the type of the shift base. We perform a
range check on the truncated shift amount, leading to false negatives.

Fix the issue (PR27271) by performing the range check on the original
shift amount.

Differential Revision: https://reviews.llvm.org/D29234

llvm-svn: 293572
This commit is contained in:
Vedant Kumar 2017-01-30 23:38:54 +00:00
parent 578cf7aae7
commit d3a601b06b
2 changed files with 56 additions and 7 deletions
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16
clang/lib/CodeGen/CGExprScalar.cpp
View File

@ -2751,8 +2751,8 @@ Value *ScalarExprEmitter::EmitShl(const BinOpInfo &Ops) {
isa<llvm::IntegerType>(Ops.LHS->getType())) { isa<llvm::IntegerType>(Ops.LHS->getType())) {
CodeGenFunction::SanitizerScope SanScope(&CGF); CodeGenFunction::SanitizerScope SanScope(&CGF);
SmallVector<std::pair<Value *, SanitizerMask>, 2> Checks; SmallVector<std::pair<Value *, SanitizerMask>, 2> Checks;
llvm::Value *WidthMinusOne = GetWidthMinusOneValue(Ops.LHS, RHS); llvm::Value *WidthMinusOne = GetWidthMinusOneValue(Ops.LHS, Ops.RHS);
llvm::Value *ValidExponent = Builder.CreateICmpULE(RHS, WidthMinusOne); llvm::Value *ValidExponent = Builder.CreateICmpULE(Ops.RHS, WidthMinusOne);
if (SanitizeExponent) { if (SanitizeExponent) {
Checks.push_back( Checks.push_back(
@ -2767,12 +2767,14 @@ Value *ScalarExprEmitter::EmitShl(const BinOpInfo &Ops) {
llvm::BasicBlock *Cont = CGF.createBasicBlock("cont"); llvm::BasicBlock *Cont = CGF.createBasicBlock("cont");
llvm::BasicBlock *CheckShiftBase = CGF.createBasicBlock("check"); llvm::BasicBlock *CheckShiftBase = CGF.createBasicBlock("check");
Builder.CreateCondBr(ValidExponent, CheckShiftBase, Cont); Builder.CreateCondBr(ValidExponent, CheckShiftBase, Cont);
llvm::Value *PromotedWidthMinusOne =
(RHS == Ops.RHS) ? WidthMinusOne
: GetWidthMinusOneValue(Ops.LHS, RHS);
CGF.EmitBlock(CheckShiftBase); CGF.EmitBlock(CheckShiftBase);
llvm::Value *BitsShiftedOff = llvm::Value *BitsShiftedOff = Builder.CreateLShr(
Builder.CreateLShr(Ops.LHS, Ops.LHS, Builder.CreateSub(PromotedWidthMinusOne, RHS, "shl.zeros",
Builder.CreateSub(WidthMinusOne, RHS, "shl.zeros", /*NUW*/ true, /*NSW*/ true),
/*NUW*/true, /*NSW*/true), "shl.check");
"shl.check");
if (CGF.getLangOpts().CPlusPlus) { if (CGF.getLangOpts().CPlusPlus) {
// In C99, we are not permitted to shift a 1 bit into the sign bit. // In C99, we are not permitted to shift a 1 bit into the sign bit.
// Under C++11's rules, shifting a 1 bit into the sign bit is // Under C++11's rules, shifting a 1 bit into the sign bit is

47
clang/test/CodeGen/ubsan-shift.c Normal file
View File

@ -0,0 +1,47 @@
// RUN: %clang_cc1 -triple=x86_64-apple-darwin -fsanitize=shift-exponent,shift-base -emit-llvm %s -o - | FileCheck %s
// CHECK-LABEL: define i32 @f1
int f1(int c, int shamt) {
// CHECK: icmp ule i32 %{{.*}}, 31, !nosanitize
// CHECK: icmp ule i32 %{{.*}}, 31, !nosanitize
return 1 << (c << shamt);
}
// CHECK-LABEL: define i32 @f2
int f2(long c, int shamt) {
// CHECK: icmp ule i32 %{{.*}}, 63, !nosanitize
// CHECK: icmp ule i64 %{{.*}}, 31, !nosanitize
return 1 << (c << shamt);
}
// CHECK-LABEL: define i32 @f3
unsigned f3(unsigned c, int shamt) {
// CHECK: icmp ule i32 %{{.*}}, 31, !nosanitize
// CHECK: icmp ule i32 %{{.*}}, 31, !nosanitize
return 1U << (c << shamt);
}
// CHECK-LABEL: define i32 @f4
unsigned f4(unsigned long c, int shamt) {
// CHECK: icmp ule i32 %{{.*}}, 63, !nosanitize
// CHECK: icmp ule i64 %{{.*}}, 31, !nosanitize
return 1U << (c << shamt);
}
// CHECK-LABEL: define i32 @f5
int f5(int c, long long shamt) {
// CHECK: icmp ule i64 %{{[0-9]+}}, 31, !nosanitize
//
// CHECK: sub nuw nsw i32 31, %sh_prom, !nosanitize
// CHECK: lshr i32 %{{.*}}, %shl.zeros, !nosanitize
return c << shamt;
}
// CHECK-LABEL: define i32 @f6
int f6(int c, int shamt) {
// CHECK: icmp ule i32 %[[WIDTH:.*]], 31, !nosanitize
//
// CHECK: sub nuw nsw i32 31, %[[WIDTH]], !nosanitize
// CHECK: lshr i32 %{{.*}}, %shl.zeros, !nosanitize
return c << shamt;
}