[PATCH] D92846: [KernelAddressSanitizer] Fix globals exclusion for indirect aliases

[Marco Elver via Phabricator via llvm-commits]

melver created this revision.
Herald added a subscriber: hiraditya.
melver requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

GlobalAlias::getAliasee() may not always point directly to a
GlobalVariable. In such cases, try to find the canonical GlobalVariable
that the alias refers to.

Link: https://github.com/ClangBuiltLinux/linux/issues/1208


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D92846

Files:
  llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp


Index: llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -792,7 +792,7 @@
                                   StringRef InternalSuffix);
   Instruction *CreateAsanModuleDtor(Module &M);
 
-  bool canInstrumentAliasedGlobal(const GlobalAlias &GA) const;
+  const GlobalVariable *getExcludedAliasedGlobal(const GlobalAlias &GA) const;
   bool shouldInstrumentGlobal(GlobalVariable *G) const;
   bool ShouldUseMachOGlobalsSection() const;
   StringRef getGlobalMetadataSection() const;
@@ -1787,8 +1787,8 @@
   }
 }
 
-bool ModuleAddressSanitizer::canInstrumentAliasedGlobal(
-    const GlobalAlias &GA) const {
+const GlobalVariable *
+ModuleAddressSanitizer::getExcludedAliasedGlobal(const GlobalAlias &GA) const {
   // In case this function should be expanded to include rules that do not just
   // apply when CompileKernel is true, either guard all existing rules with an
   // 'if (CompileKernel) { ... }' or be absolutely sure that all these rules
@@ -1797,10 +1797,26 @@
 
   // When compiling the kernel, globals that are aliased by symbols prefixed
   // by "__" are special and cannot be padded with a redzone.
-  if (GA.getName().startswith("__"))
-    return false;
-
-  return true;
+  if (!GA.getName().startswith("__"))
+    return nullptr;
+
+  const GlobalVariable *GV = dyn_cast<GlobalVariable>(GA.getAliasee());
+
+  if (!GV) {
+    // Try to find canonical GlobalVariable from GlobalAlias.
+    if (const auto *GAA = dyn_cast<GlobalAlias>(GA.getAliasee())) {
+      return getExcludedAliasedGlobal(*GAA); // Recursive aliases
+    } else if (const auto *CE = dyn_cast<ConstantExpr>(GA.getAliasee())) {
+      // Pointer into global variable; find it.
+      for (const Use &U : CE->operands()) {
+        GV = dyn_cast<GlobalVariable>(U);
+        if (GV)
+          break;
+      }
+    }
+    // Not a GlobalVariable alias, ignore.
+  }
+  return GV;
 }
 
 bool ModuleAddressSanitizer::shouldInstrumentGlobal(GlobalVariable *G) const {
@@ -2252,14 +2268,12 @@
   *CtorComdat = false;
 
   // Build set of globals that are aliased by some GA, where
-  // canInstrumentAliasedGlobal(GA) returns false.
+  // getExcludedAliasedGlobal(GA) returns the relevant GlobalVariable.
   SmallPtrSet<const GlobalVariable *, 16> AliasedGlobalExclusions;
   if (CompileKernel) {
     for (auto &GA : M.aliases()) {
-      if (const auto *GV = dyn_cast<GlobalVariable>(GA.getAliasee())) {
-        if (!canInstrumentAliasedGlobal(GA))
-          AliasedGlobalExclusions.insert(GV);
-      }
+      if (const GlobalVariable *GV = getExcludedAliasedGlobal(GA))
+        AliasedGlobalExclusions.insert(GV);
     }
   }
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D92846.310191.patch
Type: text/x-patch
Size: 2822 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20201208/3f06197b/attachment.bin>