[clang][slh] add attribute for speculative load hardening

Summary:
The prior diff had to be reverted because there were two tests
that failed. I updated the two tests in this diff

clang/test/Misc/pragma-attribute-supported-attributes-list.test
clang/test/SemaCXX/attr-speculative-load-hardening.cpp

----- Summary from Previous Diff (Still Accurate) -----

LLVM IR already has an attribute for speculative_load_hardening. Before
this commit, when a user passed the -mspeculative-load-hardening flag to
Clang, every function would have this attribute added to it. This Clang
attribute will allow users to opt into SLH on a function by function basis.

This can be applied to functions and Objective C methods.

Reviewers: chandlerc, echristo, kristof.beyls, aaron.ballman

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D54915

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@347617 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/clang/Basic/Attr.td b/include/clang/Basic/Attr.td
index a6be48c234fed482dae01f55c0989fc82d144736..5b52ba4f64bc370370fd10cffb8afb2cbd0e8e1b 100644 (file)
--- a/include/clang/Basic/Attr.td
+++ b/include/clang/Basic/Attr.td
@@ -3091,3 +3091,9 @@ def AlwaysDestroy : InheritableAttr {
   let Subjects = SubjectList<[Var]>;
   let Documentation = [AlwaysDestroyDocs];
 }
+
+def SpeculativeLoadHardening : InheritableAttr {
+  let Spellings = [Clang<"speculative_load_hardening">];
+  let Subjects = SubjectList<[Function, ObjCMethod], ErrorDiag>;
+  let Documentation = [SpeculativeLoadHardeningDocs];
+}

diff --git a/include/clang/Basic/AttrDocs.td b/include/clang/Basic/AttrDocs.td
index e38c557f140f3a591d47dd080b9b54d9d6444670..203ae827195b1494fcfedfdc85517154c8313cb0 100644 (file)
--- a/include/clang/Basic/AttrDocs.td
+++ b/include/clang/Basic/AttrDocs.td
@@ -3629,3 +3629,27 @@ GNU inline semantics are the default behavior with ``-std=gnu89``,
 ``-std=c89``, ``-std=c94``, or ``-fgnu89-inline``.
   }];
 }
+
+def SpeculativeLoadHardeningDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+  This attribute can be applied to a function declaration in order to indicate
+  that `Speculative Load Hardening <https://llvm.org/docs/SpeculativeLoadHardening.html>`_
+  should be enabled for the function body. This can also be applied to a method
+  in Objective C.
+
+  Speculative Load Hardening is a best-effort mitigation against
+  information leak attacks that make use of control flow
+  miss-speculation - specifically miss-speculation of whether a branch
+  is taken or not. Typically vulnerabilities enabling such attacks are
+  classified as "Spectre variant #1". Notably, this does not attempt to
+  mitigate against miss-speculation of branch target, classified as
+  "Spectre variant #2" vulnerabilities.
+
+  When inlining, the attribute is sticky. Inlining a function that
+  carries this attribute will cause the caller to gain the
+  attribute. This is intended to provide a maximally conservative model
+  where the code in a function annotated with this attribute will always
+  (even after inlining) end up hardened.
+  }];
+}

diff --git a/lib/CodeGen/CGCall.cpp b/lib/CodeGen/CGCall.cpp
index 0ec5c7fb45206d2c0bcc30730193092dc12fec2f..6d89f3919fd11ee0423a6dfea56ee22d46c10a97 100644 (file)
--- a/lib/CodeGen/CGCall.cpp
+++ b/lib/CodeGen/CGCall.cpp
@@ -1791,6 +1791,8 @@ void CodeGenModule::ConstructDefaultFnAttrList(StringRef Name, bool HasOptnone,
     if (CodeGenOpts.Backchain)
       FuncAttrs.addAttribute("backchain");
 
+    // FIXME: The interaction of this attribute with the SLH command line flag
+    // has not been determined.
     if (CodeGenOpts.SpeculativeLoadHardening)
       FuncAttrs.addAttribute(llvm::Attribute::SpeculativeLoadHardening);
   }
@@ -1854,6 +1856,8 @@ void CodeGenModule::ConstructAttributeList(
       FuncAttrs.addAttribute(llvm::Attribute::NoDuplicate);
     if (TargetDecl->hasAttr<ConvergentAttr>())
       FuncAttrs.addAttribute(llvm::Attribute::Convergent);
+    if (TargetDecl->hasAttr<SpeculativeLoadHardeningAttr>())
+      FuncAttrs.addAttribute(llvm::Attribute::SpeculativeLoadHardening);
 
     if (const FunctionDecl *Fn = dyn_cast<FunctionDecl>(TargetDecl)) {
       AddAttributesFromFunctionProtoType(

diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index 9f5325d109ebe0d923aaa40a687df3fd4097f04b..be662b9b914d4b6536b62cf4c51735dce9a22c9c 100644 (file)
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -6373,6 +6373,9 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case ParsedAttr::AT_Section:
     handleSectionAttr(S, D, AL);
     break;
+  case ParsedAttr::AT_SpeculativeLoadHardening:
+    handleSimpleAttribute<SpeculativeLoadHardeningAttr>(S, D, AL);
+    break;
   case ParsedAttr::AT_CodeSeg:
     handleCodeSegAttr(S, D, AL);
     break;

diff --git a/test/CodeGen/attr-speculative-load-hardening.cpp b/test/CodeGen/attr-speculative-load-hardening.cpp
new file mode 100644 (file)
index 0000000..e2eb805
--- /dev/null
+++ b/test/CodeGen/attr-speculative-load-hardening.cpp
@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -std=c++11 -disable-llvm-passes -emit-llvm %s -o - | FileCheck %s --check-prefix=CHECK1
+// RUN: %clang_cc1 -std=c++11 -disable-llvm-passes -emit-llvm %s -o - | FileCheck %s --check-prefix=CHECK2
+//
+// Check that we set the attribute on each function.
+
+[[clang::speculative_load_hardening]]
+int test1() {
+  return 42;
+}
+
+int __attribute__((speculative_load_hardening)) test2() {
+  return 42;
+}
+// CHECK1: @{{.*}}test1{{.*}}[[SLH1:#[0-9]+]]
+// CHECK1: attributes [[SLH1]] = { {{.*}}speculative_load_hardening{{.*}} }
+
+// CHECK2: @{{.*}}test2{{.*}}[[SLH2:#[0-9]+]]
+// CHECK2: attributes [[SLH2]] = { {{.*}}speculative_load_hardening{{.*}} }

diff --git a/test/CodeGen/attr-speculative-load-hardening.m b/test/CodeGen/attr-speculative-load-hardening.m
new file mode 100644 (file)
index 0000000..2de945b
--- /dev/null
+++ b/test/CodeGen/attr-speculative-load-hardening.m
@@ -0,0 +1,9 @@
+// RUN: %clang -emit-llvm %s -o - -S | FileCheck %s -check-prefix=SLH
+
+int main() __attribute__((speculative_load_hardening)) {
+  return 0;
+}
+
+// SLH: @{{.*}}main{{.*}}[[SLH:#[0-9]+]]
+
+// SLH: attributes [[SLH]] = { {{.*}}speculative_load_hardening{{.*}} }

diff --git a/test/Misc/pragma-attribute-supported-attributes-list.test b/test/Misc/pragma-attribute-supported-attributes-list.test
index 0a54c6c05adae6d793f8340cd8ac40e7c0ccb1b5..0aa923de7dfab25a975d23910c90bbe5da72e885 100644 (file)
--- a/test/Misc/pragma-attribute-supported-attributes-list.test
+++ b/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -2,7 +2,7 @@
 
 // The number of supported attributes should never go down!
 
-// CHECK: #pragma clang attribute supports 129 attributes:
+// CHECK: #pragma clang attribute supports 130 attributes:
 // CHECK-NEXT: AMDGPUFlatWorkGroupSize (SubjectMatchRule_function)
 // CHECK-NEXT: AMDGPUNumSGPR (SubjectMatchRule_function)
 // CHECK-NEXT: AMDGPUNumVGPR (SubjectMatchRule_function)
@@ -116,6 +116,7 @@
 // CHECK-NEXT: ScopedLockable (SubjectMatchRule_record)
 // CHECK-NEXT: Section (SubjectMatchRule_function, SubjectMatchRule_variable_is_global, SubjectMatchRule_objc_method, SubjectMatchRule_objc_property)
 // CHECK-NEXT: SetTypestate (SubjectMatchRule_function_is_member)
+// CHECK-NEXT: SpeculativeLoadHardening (SubjectMatchRule_function, SubjectMatchRule_objc_method)
 // CHECK-NEXT: SwiftContext (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: SwiftErrorResult (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: SwiftIndirectResult (SubjectMatchRule_variable_is_parameter)

diff --git a/test/SemaCXX/attr-speculative-load-hardening.cpp b/test/SemaCXX/attr-speculative-load-hardening.cpp
new file mode 100644 (file)
index 0000000..bba3b69
--- /dev/null
+++ b/test/SemaCXX/attr-speculative-load-hardening.cpp
@@ -0,0 +1,34 @@
+// RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify %s
+
+int i __attribute__((speculative_load_hardening)); // expected-error {{'speculative_load_hardening' attribute only applies to functions}}
+
+void f1() __attribute__((speculative_load_hardening));
+void f2() __attribute__((speculative_load_hardening(1))); // expected-error {{'speculative_load_hardening' attribute takes no arguments}}
+
+template <typename T>
+void tf1() __attribute__((speculative_load_hardening));
+
+int f3(int __attribute__((speculative_load_hardening)), int); // expected-error {{'speculative_load_hardening' attribute only applies to functions}}
+
+struct A {
+  int f __attribute__((speculative_load_hardening));  // expected-error {{'speculative_load_hardening' attribute only applies to functions}}
+  void mf1() __attribute__((speculative_load_hardening));
+  static void mf2() __attribute__((speculative_load_hardening));
+};
+
+int ci [[clang::speculative_load_hardening]]; // expected-error {{'speculative_load_hardening' attribute only applies to functions}}
+
+[[clang::speculative_load_hardening]] void cf1();
+[[clang::speculative_load_hardening(1)]] void cf2(); // expected-error {{'speculative_load_hardening' attribute takes no arguments}}
+
+template <typename T>
+[[clang::speculative_load_hardening]]
+void ctf1();
+
+int cf3(int c[[clang::speculative_load_hardening]], int); // expected-error {{'speculative_load_hardening' attribute only applies to functions}}
+
+struct CA {
+  int f [[clang::speculative_load_hardening]];  // expected-error {{'speculative_load_hardening' attribute only applies to functions}}
+  [[clang::speculative_load_hardening]] void mf1();
+  [[clang::speculative_load_hardening]] static void mf2();
+};