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.
72 lines
3.7 KiB
C
72 lines
3.7 KiB
C
// RUN: %clang_cc1 -Wall -Wno-unused -Wno-uninitialized -verify %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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void checked(void) {}
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void (*checked_ptr)(void) = unchecked; // expected-warning{{implicit conversion from 'void (void) __attribute__((cfi_unchecked_callee))' to 'void (*)(void)' discards 'cfi_unchecked_callee' attribute}}
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void (CFI_UNCHECKED_CALLEE *unchecked_ptr)(void) = unchecked;
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void (CFI_UNCHECKED_CALLEE *from_normal)(void) = checked;
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void (CFI_UNCHECKED_CALLEE *c_no_function_decay)(void) = &unchecked;
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typedef void (CFI_UNCHECKED_CALLEE unchecked_func_t)(void);
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typedef void (checked_func_t)(void);
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typedef void (CFI_UNCHECKED_CALLEE *cfi_unchecked_func_ptr_t)(void);
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typedef void (*checked_func_ptr_t)(void);
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checked_func_t *cfi_func = unchecked; // expected-warning{{implicit conversion from 'void (void) __attribute__((cfi_unchecked_callee))' to 'void (*)(void)' discards 'cfi_unchecked_callee' attribute}}
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unchecked_func_t *unchecked_func = unchecked;
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void CFI_UNCHECKED_CALLEE after_ret_type(void);
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CFI_UNCHECKED_CALLEE void before_ret_type(void);
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void (* CFI_UNCHECKED_CALLEE after_name)(void);
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void UsageOnImproperTypes() {
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int CFI_UNCHECKED_CALLEE i; // expected-warning{{'cfi_unchecked_callee' only applies to function types; type here is 'int'}}
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/// The attribute must be used only on functions with prototypes. The omission of `void` means it is not prototyped.
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void (CFI_UNCHECKED_CALLEE *noproto)(void); // expecteed-warning{{'cfi_unchecked_callee' attribute only applies to non-K&R-style functions}}
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}
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/// Explicit casts suppress the warning.
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void CheckCasts() {
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void (*should_warn)(void) = unchecked; // expected-warning{{implicit conversion from 'void (void) __attribute__((cfi_unchecked_callee))' to 'void (*)(void)' discards 'cfi_unchecked_callee' attribute}}
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void (*no_warn_c_style_cast)(void) = (void (*)(void))unchecked;
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struct B {} CFI_UNCHECKED_CALLEE b; // expected-warning{{'cfi_unchecked_callee' attribute only applies to functions and methods}}
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struct CFI_UNCHECKED_CALLEE C {} c; // expected-warning{{'cfi_unchecked_callee' attribute only applies to functions and methods}}
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CFI_UNCHECKED_CALLEE struct D {} d; // expected-warning{{'cfi_unchecked_callee' only applies to function types; type here is 'struct D'}}
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void *ptr2 = (void *)unchecked;
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}
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int checked_arg_func(checked_func_t *checked_func);
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void CheckDifferentConstructions() {
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void (CFI_UNCHECKED_CALLEE *arr[10])(void);
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void (*cfi_elem)(void) = arr[1]; // expected-warning{{implicit conversion from 'void (*)(void) __attribute__((cfi_unchecked_callee))' to 'void (*)(void)' discards 'cfi_unchecked_callee' attribute}}
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void (CFI_UNCHECKED_CALLEE *cfi_unchecked_elem)(void) = arr[1];
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int invoke = checked_arg_func(unchecked); // expected-warning{{implicit conversion from 'void (void) __attribute__((cfi_unchecked_callee))' to 'void (*)(void)' discards 'cfi_unchecked_callee' attribute}}
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}
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checked_func_t *returning_checked_func() {
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return unchecked; // expected-warning{{implicit conversion from 'void (void) __attribute__((cfi_unchecked_callee))' to 'void (*)(void)' discards 'cfi_unchecked_callee' attribute}}
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}
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void no_args(void) __attribute__((cfi_unchecked_callee(10))); // expected-error{{'cfi_unchecked_callee' attribute takes no arguments}}
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void Comparisons() {
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/// Let's be able to compare checked and unchecked pointers without warnings.
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unchecked == checked_ptr;
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checked_ptr == unchecked;
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unchecked == unchecked_ptr;
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unchecked != checked_ptr;
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checked_ptr != unchecked;
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unchecked != unchecked_ptr;
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(void (*)(void))unchecked == checked_ptr;
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checked_ptr == (void (*)(void))unchecked;
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}
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