Skip to content

[StackProtector] Fix phi handling in HasAddressTaken() #129248

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 2 commits into from
Mar 5, 2025
Merged

[StackProtector] Fix phi handling in HasAddressTaken() #129248

Show file tree
Hide file tree
Changes from 1 commit
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
9f7c0c2
[StackProtector] Fix phi handling in HasAddressTaken()
nikic Feb 27, 2025
3ac7edc
fix typo
nikic Feb 28, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
30 changes: 26 additions & 4 deletions llvm/lib/CodeGen/StackProtector.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -251,10 +251,21 @@ static bool ContainsProtectableArray(Type *Ty, Module *M, unsigned SSPBufferSize
return NeedsProtector;
}

/// Maximum remaining allocation size obsorved for a phi node, and how often
/// the allocation size has already been decreased. We only allow a limited
/// number of decreases.
struct PhiInfo {
TypeSize AllocSize;
unsigned NumDecreased = 0;
static constexpr unsigned MaxNumDecreased = 3;
PhiInfo(TypeSize AllocSize) : AllocSize(AllocSize) {}
};
using PhiMap = SmallDenseMap<const PHINode *, PhiInfo, 16>;

/// Check whether a stack allocation has its address taken.
static bool HasAddressTaken(const Instruction *AI, TypeSize AllocSize,
Module *M,
SmallPtrSet<const PHINode *, 16> &VisitedPHIs) {
PhiMap &VisitedPHIs) {
const DataLayout &DL = M->getDataLayout();
for (const User *U : AI->users()) {
const auto *I = cast<Instruction>(U);
Expand Down Expand Up @@ -325,9 +336,20 @@ static bool HasAddressTaken(const Instruction *AI, TypeSize AllocSize,
// Keep track of what PHI nodes we have already visited to ensure
// they are only visited once.
const auto *PN = cast<PHINode>(I);
if (VisitedPHIs.insert(PN).second)
if (HasAddressTaken(PN, AllocSize, M, VisitedPHIs))
auto [It, Inserted] = VisitedPHIs.try_emplace(PN, AllocSize);
if (!Inserted) {
if (TypeSize::isKnownGE(AllocSize, It->second.AllocSize))
break;

// Check again with smaller size.
if (It->second.NumDecreased == PhiInfo::MaxNumDecreased)
return true;

It->second.AllocSize = AllocSize;
++It->second.NumDecreased;
}
if (HasAddressTaken(PN, AllocSize, M, VisitedPHIs))
return true;
break;
}
case Instruction::Load:
Expand Down Expand Up @@ -377,7 +399,7 @@ bool SSPLayoutAnalysis::requiresStackProtector(Function *F,
// The set of PHI nodes visited when determining if a variable's reference has
// been taken. This set is maintained to ensure we don't visit the same PHI
// node multiple times.
SmallPtrSet<const PHINode *, 16> VisitedPHIs;
PhiMap VisitedPHIs;

unsigned SSPBufferSize = F->getFnAttributeAsParsedInteger(
"stack-protector-buffer-size", SSPLayoutInfo::DefaultSSPBufferSize);
Expand Down
30 changes: 26 additions & 4 deletions llvm/test/CodeGen/X86/stack-protector-phi.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4,16 +4,29 @@
define void @test_phi_diff_size(i1 %c) sspstrong {
; CHECK-LABEL: test_phi_diff_size:
; CHECK: # %bb.0: # %entry
; CHECK-NEXT: subq $24, %rsp
; CHECK-NEXT: .cfi_def_cfa_offset 32
; CHECK-NEXT: movq %fs:40, %rax
; CHECK-NEXT: movq %rax, {{[0-9]+}}(%rsp)
; CHECK-NEXT: testb $1, %dil
; CHECK-NEXT: je .LBB0_1
; CHECK-NEXT: # %bb.2: # %if
; CHECK-NEXT: leaq -{{[0-9]+}}(%rsp), %rax
; CHECK-NEXT: movq $0, (%rax)
; CHECK-NEXT: retq
; CHECK-NEXT: leaq {{[0-9]+}}(%rsp), %rax
; CHECK-NEXT: jmp .LBB0_3
; CHECK-NEXT: .LBB0_1:
; CHECK-NEXT: leaq -{{[0-9]+}}(%rsp), %rax
; CHECK-NEXT: leaq {{[0-9]+}}(%rsp), %rax
; CHECK-NEXT: .LBB0_3: # %join
; CHECK-NEXT: movq $0, (%rax)
; CHECK-NEXT: movq %fs:40, %rax
; CHECK-NEXT: cmpq {{[0-9]+}}(%rsp), %rax
; CHECK-NEXT: jne .LBB0_5
; CHECK-NEXT: # %bb.4: # %SP_return
; CHECK-NEXT: addq $24, %rsp
; CHECK-NEXT: .cfi_def_cfa_offset 8
; CHECK-NEXT: retq
; CHECK-NEXT: .LBB0_5: # %CallStackCheckFailBlk
; CHECK-NEXT: .cfi_def_cfa_offset 32
; CHECK-NEXT: callq __stack_chk_fail@PLT
entry:
%a = alloca i64
br i1 %c, label %if, label %join
Expand All @@ -38,6 +51,8 @@ define void @test_phi_loop(i1 %c) sspstrong {
; CHECK-NEXT: .cfi_def_cfa_register %rbp
; CHECK-NEXT: andq $-131072, %rsp # imm = 0xFFFE0000
; CHECK-NEXT: subq $262144, %rsp # imm = 0x40000
; CHECK-NEXT: movq %fs:40, %rax
; CHECK-NEXT: movq %rax, {{[0-9]+}}(%rsp)
; CHECK-NEXT: movq %rsp, %rax
; CHECK-NEXT: .p2align 4
; CHECK-NEXT: .LBB1_1: # %loop
Expand All @@ -47,10 +62,17 @@ define void @test_phi_loop(i1 %c) sspstrong {
; CHECK-NEXT: testb $1, %dil
; CHECK-NEXT: jne .LBB1_1
; CHECK-NEXT: # %bb.2: # %exit
; CHECK-NEXT: movq %fs:40, %rax
; CHECK-NEXT: cmpq {{[0-9]+}}(%rsp), %rax
; CHECK-NEXT: jne .LBB1_4
; CHECK-NEXT: # %bb.3: # %SP_return
; CHECK-NEXT: movq %rbp, %rsp
; CHECK-NEXT: popq %rbp
; CHECK-NEXT: .cfi_def_cfa %rsp, 8
; CHECK-NEXT: retq
; CHECK-NEXT: .LBB1_4: # %CallStackCheckFailBlk
; CHECK-NEXT: .cfi_def_cfa %rbp, 16
; CHECK-NEXT: callq __stack_chk_fail@PLT
entry:
%a = alloca <10000 x i64>
br label %loop
Expand Down
Loading