[msan] intercept dlopen and clear shadow for it

Summary:
The loader does not call mmap() through the PLT because it has to
bootstrap the process before libc is present.  Hooking dlopen() isn't
enough either because the loader runs module initializers before
returning, and they could run arbitrary msan instrumented code.

If msandr is present, then we can intercept the mmaps from dlopen at the
syscall layer and clear the shadow there.  If msandr is missing, we
clear the shadow after dlopen() and hope any initializers are trivial.

Reviewers: eugenis

CC: kcc, llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D509

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@176818 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/msan/msan.cc b/lib/msan/msan.cc
index cfa074182..96f99d4a8 100644
--- a/lib/msan/msan.cc
+++ b/lib/msan/msan.cc
@@ -59,6 +59,7 @@ static THREADLOCAL struct {
 } __msan_stack_bounds;
 
 static THREADLOCAL bool is_in_symbolizer;
+static THREADLOCAL bool is_in_loader;
 
 extern "C" const int __msan_track_origins;
 int __msan_get_track_origins() {
@@ -87,6 +88,14 @@ void EnterSymbolizer() { is_in_symbolizer = true; }
 void ExitSymbolizer()  { is_in_symbolizer = false; }
 bool IsInSymbolizer() { return is_in_symbolizer; }
 
+void EnterLoader() { is_in_loader = true; }
+void ExitLoader()  { is_in_loader = false; }
+
+extern "C" {
+SANITIZER_INTERFACE_ATTRIBUTE
+bool __msan_is_in_loader() { return is_in_loader; }
+}
+
 static Flags msan_flags;
 
 Flags *flags() {