[dfsan] Fix Endianess issue (#162881)

Fix Endianess issue with getting shadow 4 bytes corresponding to the
first origin pointer.

---------

Co-authored-by: anoopkg6 <[email protected]>

Author: anoopkg6

compiler-rt/test/dfsan/origin_endianness.c

@@ -0,0 +1,37 @@
+// RUN: %clang_dfsan -gmlt -mllvm -dfsan-track-origins=1 %s -o %t && \
+// RUN:     %run %t >%t.out 2>&1
+// RUN: FileCheck %s < %t.out
+//
+// Test origin tracking is accurate in terms of endianness.
+
+#include <sanitizer/dfsan_interface.h>
+
+typedef uint64_t FULL_TYPE;
+typedef uint32_t HALF_TYPE;
+
+__attribute__((noinline)) FULL_TYPE foo(FULL_TYPE a, FULL_TYPE b) {
+  return a + b;
+}
+
+int main(int argc, char *argv[]) {
+  FULL_TYPE a = 1;
+  FULL_TYPE b = 10;
+  dfsan_set_label(4, (HALF_TYPE *)&a, sizeof(HALF_TYPE));
+  FULL_TYPE c = foo(a, b);
+  dfsan_print_origin_trace(&c, NULL);
+  dfsan_print_origin_trace((HALF_TYPE *)&c, NULL);
+}
+
+// CHECK: Taint value 0x4 {{.*}} origin tracking ()
+// CHECK: Origin value: {{.*}}, Taint value was stored to memory at
+// CHECK: #0 {{.*}} in main {{.*}}origin_endianness.c:[[@LINE-7]]
+
+// CHECK: Origin value: {{.*}}, Taint value was created at
+// CHECK: #0 {{.*}} in main {{.*}}origin_endianness.c:[[@LINE-11]]
+
+// CHECK: Taint value 0x4 {{.*}} origin tracking ()
+// CHECK: Origin value: {{.*}}, Taint value was stored to memory at
+// CHECK: #0 {{.*}} in main {{.*}}origin_endianness.c:[[@LINE-14]]
+
+// CHECK: Origin value: {{.*}}, Taint value was created at
+// CHECK: #0 {{.*}} in main {{.*}}origin_endianness.c:[[@LINE-18]]

llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp

@@ -2191,8 +2191,16 @@ std::pair<Value *, Value *> DFSanFunction::loadShadowFast(
       // and then the entire shadow for the second origin pointer (which will be
       // chosen by combineOrigins() iff the least-significant half of the wide
       // shadow was empty but the other half was not).
-      Value *WideShadowLo = IRB.CreateShl(
-          WideShadow, ConstantInt::get(WideShadowTy, WideShadowBitWidth / 2));
+      Value *WideShadowLo =
+          F->getParent()->getDataLayout().isLittleEndian()
+              ? IRB.CreateShl(
+                    WideShadow,
+                    ConstantInt::get(WideShadowTy, WideShadowBitWidth / 2))
+              : IRB.CreateAnd(
+                    WideShadow,
+                    ConstantInt::get(WideShadowTy,
+                                     (1 - (1 << (WideShadowBitWidth / 2)))
+                                         << (WideShadowBitWidth / 2)));
       Shadows.push_back(WideShadow);
       Origins.push_back(DFS.loadNextOrigin(Pos, OriginAlign, &OriginAddr));