r367067 - [Sema] add -Walloca to flag uses of `alloca`

[George Burgess IV via cfe-commits]

Author: gbiv
Date: Thu Jul 25 15:23:40 2019
New Revision: 367067

URL: http://llvm.org/viewvc/llvm-project?rev=367067&view=rev
Log:
[Sema] add -Walloca to flag uses of `alloca`

This CL adds an optional warning to diagnose uses of the
`__builtin_alloca` family of functions. The use of these functions is
discouraged by many, so it seems like a good idea to allow clang to warn
about it.

Patch by Elaina Guan!

Differential Revision: https://reviews.llvm.org/D64883

Added:
    cfe/trunk/test/Sema/warn-alloca.c
Modified:
    cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
    cfe/trunk/lib/Sema/SemaChecking.cpp

Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=367067&r1=367066&r2=367067&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Thu Jul 25 15:23:40 2019
@@ -2779,6 +2779,11 @@ def err_no_accessor_for_property : Error
 def err_cannot_find_suitable_accessor : Error<
   "cannot find suitable %select{getter|setter}0 for property %1">;
 
+def warn_alloca : Warning<
+  "use of function %0 is discouraged; there is no way to check for failure but "
+  "failure may still occur, resulting in a possibly exploitable security vulnerability">,
+  InGroup<DiagGroup<"alloca">>, DefaultIgnore;
+
 def warn_alloca_align_alignof : Warning<
   "second argument to __builtin_alloca_with_align is supposed to be in bits">,
   InGroup<DiagGroup<"alloca-with-align-alignof">>;

Modified: cfe/trunk/lib/Sema/SemaChecking.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp?rev=367067&r1=367066&r2=367067&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaChecking.cpp (original)
+++ cfe/trunk/lib/Sema/SemaChecking.cpp Thu Jul 25 15:23:40 2019
@@ -1179,6 +1179,10 @@ Sema::CheckBuiltinFunctionCall(FunctionD
   case Builtin::BI__builtin_alloca_with_align:
     if (SemaBuiltinAllocaWithAlign(TheCall))
       return ExprError();
+    LLVM_FALLTHROUGH;
+  case Builtin::BI__builtin_alloca:
+    Diag(TheCall->getBeginLoc(), diag::warn_alloca)
+        << TheCall->getDirectCallee();
     break;
   case Builtin::BI__assume:
   case Builtin::BI__builtin_assume:

Added: cfe/trunk/test/Sema/warn-alloca.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/warn-alloca.c?rev=367067&view=auto
==============================================================================
--- cfe/trunk/test/Sema/warn-alloca.c (added)
+++ cfe/trunk/test/Sema/warn-alloca.c Thu Jul 25 15:23:40 2019
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -DSILENCE -fsyntax-only -verify -Wall %s
+// RUN: %clang_cc1 -fsyntax-only -verify -Walloca %s
+
+#ifdef SILENCE
+  // expected-no-diagnostics
+#endif
+
+void test1(int a) {
+  __builtin_alloca(a);
+#ifndef SILENCE
+  // expected-warning at -2 {{use of function '__builtin_alloca' is discouraged; there is no way to check for failure but failure may still occur, resulting in a possibly exploitable security vulnerability}}
+#endif
+}
+
+void test2(int a) {
+  __builtin_alloca_with_align(a, 32);
+#ifndef SILENCE
+  // expected-warning at -2 {{use of function '__builtin_alloca_with_align' is discouraged; there is no way to check for failure but failure may still occur, resulting in a possibly exploitable security vulnerability}}
+#endif
+}