commit 9d045a5c1e6b7b32cec8bcf140e5bffa5ac812bd
author George Burgess IV <george.burgess.iv@gmail.com> Thu Jul 25 22:23:40 2019 +0000
committer George Burgess IV <george.burgess.iv@gmail.com> Thu Jul 25 22:23:40 2019 +0000
tree 9a9d76c2f39b252b739eb5c8812fb638f0f77c03
parent 29af3b4e67713e929b3022d96c8e54408ed9cf46

[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

llvm-svn: 367067

clang/include/clang/Basic/DiagnosticSemaKinds.td

diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index e58a0b1..d5e3b76 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2779,6 +2779,11 @@
 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">>;

clang/lib/Sema/SemaChecking.cpp

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index f9f82cd..436e17a 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -1179,6 +1179,10 @@
   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:

clang/test/Sema/warn-alloca.c

diff --git a/clang/test/Sema/warn-alloca.c b/clang/test/Sema/warn-alloca.c
new file mode 100644
index 0000000..0990e11
--- /dev/null
+++ b/clang/test/Sema/warn-alloca.c
@@ -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@-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@-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
+}