[libFuzzer] Unpoison parameters before calling user callback.
Summary:
Fixes an MSan false positive when compiling with
-fsanitize=memory,fuzzer.
See https://github.com/google/oss-fuzz/issues/2369 for more details.
Reviewers: kcc
Reviewed By: kcc
Subscribers: llvm-commits, metzman, eugenis
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D61753
llvm-svn: 360390
diff --git a/compiler-rt/lib/fuzzer/FuzzerExtFunctions.def b/compiler-rt/lib/fuzzer/FuzzerExtFunctions.def
index 288a59c..41fa0fd 100644
--- a/compiler-rt/lib/fuzzer/FuzzerExtFunctions.def
+++ b/compiler-rt/lib/fuzzer/FuzzerExtFunctions.def
@@ -46,3 +46,4 @@
EXT_FUNC(__msan_scoped_disable_interceptor_checks, void, (), false);
EXT_FUNC(__msan_scoped_enable_interceptor_checks, void, (), false);
EXT_FUNC(__msan_unpoison, void, (const volatile void *, size_t size), false);
+EXT_FUNC(__msan_unpoison_param, void, (size_t n), false);
diff --git a/compiler-rt/lib/fuzzer/FuzzerLoop.cpp b/compiler-rt/lib/fuzzer/FuzzerLoop.cpp
index d1ad3e3..cb3d821 100644
--- a/compiler-rt/lib/fuzzer/FuzzerLoop.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerLoop.cpp
@@ -542,6 +542,8 @@
memcpy(DataCopy, Data, Size);
if (EF->__msan_unpoison)
EF->__msan_unpoison(DataCopy, Size);
+ if (EF->__msan_unpoison_param)
+ EF->__msan_unpoison_param(2);
if (CurrentUnitData && CurrentUnitData != Data)
memcpy(CurrentUnitData, Data, Size);
CurrentUnitSize = Size;
@@ -702,7 +704,7 @@
break; // We will mutate this input more in the next rounds.
}
if (Options.ReduceDepth && !FoundUniqFeatures)
- break;
+ break;
}
}
diff --git a/compiler-rt/test/fuzzer/MsanParamUnpoison.cpp b/compiler-rt/test/fuzzer/MsanParamUnpoison.cpp
new file mode 100644
index 0000000..bcf5080
--- /dev/null
+++ b/compiler-rt/test/fuzzer/MsanParamUnpoison.cpp
@@ -0,0 +1,28 @@
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// Triggers the bug described here:
+// https://github.com/google/oss-fuzz/issues/2369#issuecomment-490240627
+//
+// In a nutshell, MSan's parameter shadow does not get unpoisoned before calls
+// to LLVMFuzzerTestOneInput. This test case causes the parameter shadow to be
+// poisoned by the call to foo(), which will trigger an MSan false positive on
+// the Size == 0 check if the parameter shadow is still poisoned.
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+
+volatile int zero = 0;
+__attribute__((noinline)) int foo(int arg1, int arg2) { return zero; }
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+ if (Size == 0)
+ return 0;
+
+ // Pass uninitialized values to foo(). Since foo doesn't do anything with
+ // them, MSan should not report an error here.
+ int a, b;
+ return foo(a, b);
+}
diff --git a/compiler-rt/test/fuzzer/msan-param-unpoison.test b/compiler-rt/test/fuzzer/msan-param-unpoison.test
new file mode 100644
index 0000000..f32f851
--- /dev/null
+++ b/compiler-rt/test/fuzzer/msan-param-unpoison.test
@@ -0,0 +1,5 @@
+REQUIRES: msan
+RUN: %msan_compiler %S/MsanParamUnpoison.cpp -o %t
+RUN: %run %t -seed=1 -runs=1000 2>&1 | FileCheck %s
+
+CHECK-NOT: MemorySanitizer: use-of-uninitialized-value