Use PROT_NONE on the unused parts of CFI shadow. am: c3b3e869ce am: bca71db10d

Original change: https://googleplex-android-review.googlesource.com/c/platform/bionic/+/11760912

Change-Id: I4cb258a190f0e70d57ac36646800f74665e27855

2 files changed, 5 insertions, 7 deletions

diff --git a/linker/linker_cfi.cpp b/linker/linker_cfi.cpp
index 5995013b4..87b5d3485 100644
--- a/linker/linker_cfi.cpp
+++ b/linker/linker_cfi.cpp
@@ -56,6 +56,7 @@ class ShadowWrite {
         reinterpret_cast<char*>(mmap(nullptr, aligned_end - aligned_start, PROT_READ | PROT_WRITE,
                                      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0));
     CHECK(tmp_start != MAP_FAILED);
+    mprotect(aligned_start, aligned_end - aligned_start, PROT_READ);
     memcpy(tmp_start, aligned_start, shadow_start - aligned_start);
     memcpy(tmp_start + (shadow_end - aligned_start), shadow_end, aligned_end - shadow_end);
   }
@@ -154,7 +155,7 @@ uintptr_t soinfo_find_cfi_check(soinfo* si) {
 
 uintptr_t CFIShadowWriter::MapShadow() {
   void* p =
-      mmap(nullptr, kShadowSize, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, -1, 0);
+      mmap(nullptr, kShadowSize, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, -1, 0);
   CHECK(p != MAP_FAILED);
   return reinterpret_cast<uintptr_t>(p);
 }
diff --git a/tests/libs/cfi_test_lib.cpp b/tests/libs/cfi_test_lib.cpp
index 9f456d39b..6f551c5f8 100644
--- a/tests/libs/cfi_test_lib.cpp
+++ b/tests/libs/cfi_test_lib.cpp
@@ -67,12 +67,9 @@ struct A {
   void check_cfi_self() {
     g_last_type_id = 0;
     assert(&__cfi_slowpath);
-    // CFI check for an invalid address. Normally, this would kill the process by routing the call
-    // back to the calling module's __cfi_check, which does the right thing based on
-    // -fsanitize-recover / -fsanitize-trap. But this module has custom __cfi_check that does not do
-    // any of that, so the result looks like a passing check.
-    int zz;
-    __cfi_slowpath(13, static_cast<void*>(&zz));
+    // CFI check for an address inside this DSO. This goes to the current module's __cfi_check,
+    // which updates g_last_type_id.
+    __cfi_slowpath(13, static_cast<void*>(&g_last_type_id));
     assert(g_last_type_id == 13);
     // CFI check for a libc function. This never goes into this module's __cfi_check, and must pass.
     __cfi_slowpath(14, reinterpret_cast<void*>(&exit));