Author: yln
Date: Wed Jan 23 17:06:19 2019
New Revision: 352003
URL: http://llvm.org/viewvc/llvm-project?rev=352003&view=rev
Log:
[Sanitizers] UBSan unreachable incompatible with ASan in the presence of
`noreturn` calls
Summary:
UBSan wants to detect when unreachable code is actually reached, so it
adds instrumentation before every `unreachable` instruction. However,
the optimizer will remove code after calls to functions marked with
`noreturn`. To avoid this UBSan removes `noreturn` from both the call
instruction as well as from the function itself. Unfortunately, ASan
relies on this annotation to unpoison the stack by inserting calls to
`_asan_handle_no_return` before `noreturn` functions. This is important
for functions that do not return but access the the stack memory, e.g.,
unwinder functions *like* `longjmp` (`longjmp` itself is actually
"double-proofed" via its interceptor). The result is that when ASan and
UBSan are combined, the `noreturn` attributes are missing and ASan
cannot unpoison the stack, so it has false positives when stack
unwinding is used.
Changes:
# UBSan now adds the `expect_noreturn` attribute whenever it removes
the `noreturn` attribute from a function
# ASan additionally checks for the presence of this attribute
Generated code:
```
call void @__asan_handle_no_return // Additionally inserted to avoid false
positives
call void @longjmp
call void @__asan_handle_no_return
call void @__ubsan_handle_builtin_unreachable
unreachable
```
The second call to `__asan_handle_no_return` is redundant. This will be
cleaned up in a follow-up patch.
rdar://problem/40723397
Reviewers: delcypher, eugenis
Tags: #sanitizers
Differential Revision: https://reviews.llvm.org/D56624
Modified:
cfe/trunk/lib/CodeGen/CGCall.cpp
cfe/trunk/test/CodeGenCXX/ubsan-unreachable.cpp
Modified: cfe/trunk/lib/CodeGen/CGCall.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGCall.cpp?rev=352003&r1=352002&r2=352003&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CGCall.cpp (original)
+++ cfe/trunk/lib/CodeGen/CGCall.cpp Wed Jan 23 17:06:19 2019
@@ -4401,12 +4401,16 @@ RValue CodeGenFunction::EmitCall(const C
if (UnusedReturnSizePtr)
PopCleanupBlock();
- // Strip away the noreturn attribute to better diagnose unreachable UB.
+ // Replace the noreturn attribute to better diagnose unreachable UB.
if (SanOpts.has(SanitizerKind::Unreachable)) {
+ // Also remove from function since CS.hasFnAttr(..) also checks
attributes
+ // of the called function.
if (auto *F = CS.getCalledFunction())
F->removeFnAttr(llvm::Attribute::NoReturn);
CS.removeAttribute(llvm::AttributeList::FunctionIndex,
llvm::Attribute::NoReturn);
+ CS.addAttribute(llvm::AttributeList::FunctionIndex,
+ llvm::Attribute::ExpectNoReturn);
}
EmitUnreachable(Loc);
Modified: cfe/trunk/test/CodeGenCXX/ubsan-unreachable.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/ubsan-unreachable.cpp?rev=352003&r1=352002&r2=352003&view=diff
==============================================================================
--- cfe/trunk/test/CodeGenCXX/ubsan-unreachable.cpp (original)
+++ cfe/trunk/test/CodeGenCXX/ubsan-unreachable.cpp Wed Jan 23 17:06:19 2019
@@ -2,38 +2,35 @@
extern void __attribute__((noreturn)) abort();
-// CHECK-LABEL: define void @_Z14calls_noreturnv
+// CHECK-LABEL: define void @_Z14calls_noreturnv()
void calls_noreturn() {
+ // CHECK: call void @_Z5abortv() [[CALL_SITE_ATTR:#[0-9]+]]
abort();
- // Check that there are no attributes on the call site.
- // CHECK-NOT: call void @_Z5abortv{{.*}}#
-
// CHECK: __ubsan_handle_builtin_unreachable
// CHECK: unreachable
}
struct A {
- // CHECK: declare void @_Z5abortv{{.*}} [[ABORT_ATTR:#[0-9]+]]
+ // CHECK: declare void @_Z5abortv() [[EXTERN_FN_ATTR:#[0-9]+]]
// CHECK-LABEL: define linkonce_odr void @_ZN1A5call1Ev
void call1() {
- // CHECK-NOT: call void @_ZN1A16does_not_return2Ev{{.*}}#
+ // CHECK: call void @_ZN1A16does_not_return2Ev({{.*}}) [[CALL_SITE_ATTR]]
does_not_return2();
// CHECK: __ubsan_handle_builtin_unreachable
// CHECK: unreachable
}
- // Test static members.
+ // Test static members. Checks are below after `struct A` scope ends.
static void __attribute__((noreturn)) does_not_return1() {
- // CHECK-NOT: call void @_Z5abortv{{.*}}#
abort();
}
// CHECK-LABEL: define linkonce_odr void @_ZN1A5call2Ev
void call2() {
- // CHECK-NOT: call void @_ZN1A16does_not_return1Ev{{.*}}#
+ // CHECK: call void @_ZN1A16does_not_return1Ev() [[CALL_SITE_ATTR]]
does_not_return1();
// CHECK: __ubsan_handle_builtin_unreachable
@@ -46,18 +43,18 @@ struct A {
// CHECK-LABEL: define linkonce_odr void @_ZN1A5call3Ev
void call3() {
MemFn MF = &A::does_not_return2;
+ // CHECK: call void %{{[0-9]+\(.*}}) [[CALL_SITE_ATTR]]
(this->*MF)();
- // CHECK-NOT: call void %{{.*}}#
// CHECK: __ubsan_handle_builtin_unreachable
// CHECK: unreachable
}
// Test regular members.
// CHECK-LABEL: define linkonce_odr void @_ZN1A16does_not_return2Ev({{.*}})
- // CHECK-SAME: [[DOES_NOT_RETURN_ATTR:#[0-9]+]]
+ // CHECK-SAME: [[USER_FN_ATTR:#[0-9]+]]
void __attribute__((noreturn)) does_not_return2() {
- // CHECK-NOT: call void @_Z5abortv(){{.*}}#
+ // CHECK: call void @_Z5abortv() [[CALL_SITE_ATTR]]
abort();
// CHECK: call void @__ubsan_handle_builtin_unreachable
@@ -68,7 +65,9 @@ struct A {
}
};
-// CHECK: define linkonce_odr void @_ZN1A16does_not_return1Ev()
[[DOES_NOT_RETURN_ATTR]]
+// CHECK-LABEL: define linkonce_odr void @_ZN1A16does_not_return1Ev()
+// CHECK-SAME: [[USER_FN_ATTR]]
+// CHECK: call void @_Z5abortv() [[CALL_SITE_ATTR]]
void force_irgen() {
A a;
@@ -77,5 +76,9 @@ void force_irgen() {
a.call3();
}
-// CHECK-NOT: [[ABORT_ATTR]] = {{[^}]+}}noreturn
-// CHECK-NOT: [[DOES_NOT_RETURN_ATTR]] = {{[^}]+}}noreturn
+// 1) 'noreturn' should be removed from functions and call sites
+// 2) 'expect_noreturn' added to call sites
+// CHECK-LABEL: attributes
+// CHECK: [[USER_FN_ATTR]] = { {{.*[^noreturn].*}} }
+// CHECK: [[EXTERN_FN_ATTR]] = { {{.*[^noreturn].*}} }
+// CHECK: [[CALL_SITE_ATTR]] = { expect_noreturn }
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