b194cf1e40
This introduces the attribute discussed in https://discourse.llvm.org/t/rfc-function-type-attribute-to-prevent-cfi-instrumentation/85458. The proposed name has been changed from `no_cfi` to `cfi_unchecked_callee` to help differentiate from `no_sanitize("cfi")` more easily. The proposed attribute has the following semantics: 1. Indirect calls to a function type with this attribute will not be instrumented with CFI. That is, the indirect call will not be checked. Note that this only changes the behavior for indirect calls on pointers to function types having this attribute. It does not prevent all indirect function calls for a given type from being checked. 2. All direct references to a function whose type has this attribute will always reference the true function definition rather than an entry in the CFI jump table. 3. When a pointer to a function with this attribute is implicitly cast to a pointer to a function without this attribute, the compiler will give a warning saying this attribute is discarded. This warning can be silenced with an explicit C-style cast or C++ static_cast.
78 lines
3.3 KiB
C++
78 lines
3.3 KiB
C++
// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -fsanitize=cfi-icall -o - %s | FileCheck %s
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#define CFI_UNCHECKED_CALLEE __attribute__((cfi_unchecked_callee))
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void unchecked(void) CFI_UNCHECKED_CALLEE {}
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/// All references to unchecked function with `cfi_unchecked_callee` should have the `cfi_unchecked_callee` wrapper.
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// CHECK: @checked = global ptr no_cfi @_Z9uncheckedv
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void (*checked)(void) = unchecked;
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// CHECK: @unchecked2 = global ptr no_cfi @_Z9uncheckedv
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void (CFI_UNCHECKED_CALLEE *unchecked2)(void) = unchecked;
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// CHECK: @checked2 = global ptr no_cfi @_Z9uncheckedv
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constexpr void (CFI_UNCHECKED_CALLEE *unchecked_constexpr)(void) = unchecked;
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void (*checked2)(void) = unchecked_constexpr;
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/// Note we still reference the `no_cfi` function rather than the jump table entry.
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/// The explicit cast will only silence the warning.
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// CHECK: @checked_explicit_cast = global ptr no_cfi @_Z9uncheckedv
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void (*checked_explicit_cast)(void) = (void (*)(void))unchecked;
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// CHECK: @checked_array = global [3 x ptr] [ptr no_cfi @_Z9uncheckedv, ptr no_cfi @_Z9uncheckedv, ptr no_cfi @_Z9uncheckedv]
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void (*checked_array[])(void) = {
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unchecked,
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(void (*)(void))unchecked,
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reinterpret_cast<void (*)(void)>(unchecked),
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};
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void func_accepting_checked(void (*p)(void)) {}
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// CHECK-LABEL: _Z9InvokeCFIv
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void InvokeCFI() {
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// CHECK: %0 = load ptr, ptr @checked, align 8
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// CHECK: %1 = call i1 @llvm.type.test(ptr %0, metadata !"_ZTSFvvE")
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checked();
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}
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// CHECK-LABEL: _Z11InvokeNoCFIv
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void InvokeNoCFI() {
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// CHECK: %0 = load ptr, ptr @unchecked2, align 8
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// CHECK: call void %0()
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unchecked2();
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}
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struct A {
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void unchecked_method() CFI_UNCHECKED_CALLEE {}
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virtual void unchecked_virtual_method() CFI_UNCHECKED_CALLEE {}
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static void unchecked_static_method() CFI_UNCHECKED_CALLEE {}
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int unchecked_const_method() const CFI_UNCHECKED_CALLEE { return 0; }
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int unchecked_const_method_int_arg(int n) const CFI_UNCHECKED_CALLEE { return 0; }
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};
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void h(void) {
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// CHECK: store ptr no_cfi @_Z9uncheckedv, ptr %unchecked_local
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void (*unchecked_local)(void) = unchecked;
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// CHECK: call void @_Z22func_accepting_checkedPFvvE(ptr noundef no_cfi @_Z9uncheckedv)
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func_accepting_checked(unchecked);
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// CHECK: [[B:%.*]] = load ptr, ptr @checked
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// CHECK-NEXT: call void @_Z22func_accepting_checkedPFvvE(ptr noundef [[B]])
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func_accepting_checked(checked);
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// CHECK: store { i64, i64 } { i64 ptrtoint (ptr no_cfi @_ZN1A16unchecked_methodEv to i64), i64 0 }, ptr %A1
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auto A1 = &A::unchecked_method;
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/// Storing unchecked virtual function pointer stores an offset instead. This is part of the
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/// normal Itanium C++ ABI, but let's make sure we don't change anything.
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// CHECK: store { i64, i64 } { i64 1, i64 0 }, ptr %A2
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auto A2 = &A::unchecked_virtual_method;
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// CHECK: store ptr no_cfi @_ZN1A23unchecked_static_methodEv, ptr %A3
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auto A3 = &A::unchecked_static_method;
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// CHECK: store { i64, i64 } { i64 ptrtoint (ptr no_cfi @_ZNK1A22unchecked_const_methodEv to i64), i64 0 }, ptr %A4
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auto A4 = (int(CFI_UNCHECKED_CALLEE A::*)() const)(&A::unchecked_const_method);
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// CHECK: store { i64, i64 } { i64 ptrtoint (ptr no_cfi @_ZNK1A30unchecked_const_method_int_argEi to i64), i64 0 }, ptr %A5
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auto A5 = (int(CFI_UNCHECKED_CALLEE A::*)(int) const)(&A::unchecked_const_method_int_arg);
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}
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