Protection against stack-based memory corruption errors using SafeStack

This patch adds the safe stack instrumentation pass to LLVM, which separates the program stack into a safe stack, which stores return addresses, register spills, and local variables that are statically verified to be accessed in a safe way, and the unsafe stack, which stores everything else. Such separation makes it much harder for an attacker to corrupt objects on the safe stack, including function pointers stored in spilled registers and return addresses. You can find more information about the safe stack, as well as other parts of or control-flow hijack protection technique in our OSDI paper on code-pointer integrity (http://dslab.epfl.ch/pubs/cpi.pdf) and our project website (http://levee.epfl.ch). The overhead of our implementation of the safe stack is very close to zero (0.01% on the Phoronix benchmarks). This is lower than the overhead of stack cookies, which are supported by LLVM and are commonly used today, yet the security guarantees of the safe stack are strictly stronger than stack cookies. In some cases, the safe stack improves performance due to better cache locality. Our current implementation of the safe stack is stable and robust, we used it to recompile multiple projects on Linux including Chromium, and we also recompiled the entire FreeBSD user-space system and more than 100 packages. We ran unit tests on the FreeBSD system and many of the packages and observed no errors caused by the safe stack. The safe stack is also fully binary compatible with non-instrumented code and can be applied to parts of a program selectively. This patch is our implementation of the safe stack on top of LLVM. The patches make the following changes: - Add the safestack function attribute, similar to the ssp, sspstrong and sspreq attributes. - Add the SafeStack instrumentation pass that applies the safe stack to all functions that have the safestack attribute. This pass moves all unsafe local variables to the unsafe stack with a separate stack pointer, whereas all safe variables remain on the regular stack that is managed by LLVM as usual. - Invoke the pass as the last stage before code generation (at the same time the existing cookie-based stack protector pass is invoked). - Add unit tests for the safe stack. Original patch by Volodymyr Kuznetsov and others at the Dependable Systems Lab at EPFL; updates and upstreaming by myself. Differential Revision: http://reviews.llvm.org/D6094 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239761 91177308-0d34-0410-b5e6-96231b3b80d8
llvm-mirror · Jun 15, 2015 · 7ffec83 · 7ffec83
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diff --git a/docs/LangRef.rst b/docs/LangRef.rst
@@ -1319,6 +1319,15 @@ example:
     ``setjmp`` is an example of such a function. The compiler disables
     some optimizations (like tail calls) in the caller of these
     functions.
+``safestack``
+    This attribute indicates that
+    `SafeStack <http://clang.llvm.org/docs/SafeStack.html>`_
+    protection is enabled for this function.
+
+    If a function that has a ``safestack`` attribute is inlined into a
+    function that doesn't have a ``safestack`` attribute or which has an
+    ``ssp``, ``sspstrong`` or ``sspreq`` attribute, then the resulting
+    function will have a ``safestack`` attribute.
 ``sanitize_address``
     This attribute indicates that AddressSanitizer checks
     (dynamic address safety analysis) are enabled for this function.

diff --git a/include/llvm/Bitcode/LLVMBitCodes.h b/include/llvm/Bitcode/LLVMBitCodes.h
@@ -403,7 +403,8 @@ namespace bitc {
     ATTR_KIND_JUMP_TABLE = 40,
     ATTR_KIND_DEREFERENCEABLE = 41,
     ATTR_KIND_DEREFERENCEABLE_OR_NULL = 42,
-    ATTR_KIND_CONVERGENT = 43
+    ATTR_KIND_CONVERGENT = 43,
+    ATTR_KIND_SAFESTACK = 44,
   };
 
   enum ComdatSelectionKindCodes {

diff --git a/include/llvm/IR/Attributes.h b/include/llvm/IR/Attributes.h
@@ -108,6 +108,7 @@ class Attribute {
     StackProtect,          ///< Stack protection.
     StackProtectReq,       ///< Stack protection required.
     StackProtectStrong,    ///< Strong Stack protection.
+    SafeStack,             ///< Safe Stack protection.
     StructRet,             ///< Hidden pointer to structure to return
     SanitizeAddress,       ///< AddressSanitizer is on.
     SanitizeThread,        ///< ThreadSanitizer is on.

diff --git a/include/llvm/InitializePasses.h b/include/llvm/InitializePasses.h
@@ -242,6 +242,7 @@ void initializeRegionOnlyViewerPass(PassRegistry&);
 void initializeRegionPrinterPass(PassRegistry&);
 void initializeRegionViewerPass(PassRegistry&);
 void initializeRewriteStatepointsForGCPass(PassRegistry&);
+void initializeSafeStackPass(PassRegistry&);
 void initializeSCCPPass(PassRegistry&);
 void initializeSROAPass(PassRegistry&);
 void initializeSROA_DTPass(PassRegistry&);

diff --git a/include/llvm/LinkAllPasses.h b/include/llvm/LinkAllPasses.h
@@ -131,6 +131,7 @@ namespace {
       (void) llvm::createRegionPrinterPass();
       (void) llvm::createRegionViewerPass();
       (void) llvm::createSCCPPass();
+      (void) llvm::createSafeStackPass();
       (void) llvm::createScalarReplAggregatesPass();
       (void) llvm::createSingleLoopExtractorPass();
       (void) llvm::createStripSymbolsPass();

diff --git a/include/llvm/Transforms/Instrumentation.h b/include/llvm/Transforms/Instrumentation.h
@@ -132,6 +132,10 @@ inline ModulePass *createDataFlowSanitizerPassForJIT(
 // checking on loads, stores, and other memory intrinsics.
 FunctionPass *createBoundsCheckingPass();
 
+/// \brief This pass splits the stack into a safe stack and an unsafe stack to
+/// protect against stack-based overflow vulnerabilities.
+FunctionPass *createSafeStackPass();
+
 } // End llvm namespace
 
 #endif
diff --git a/lib/AsmParser/LLLexer.cpp b/lib/AsmParser/LLLexer.cpp
@@ -628,6 +628,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(ssp);
   KEYWORD(sspreq);
   KEYWORD(sspstrong);
+  KEYWORD(safestack);
   KEYWORD(sanitize_address);
   KEYWORD(sanitize_thread);
   KEYWORD(sanitize_memory);

diff --git a/lib/AsmParser/LLParser.cpp b/lib/AsmParser/LLParser.cpp
@@ -958,6 +958,7 @@ bool LLParser::ParseFnAttributeValuePairs(AttrBuilder &B,
     case lltok::kw_ssp:               B.addAttribute(Attribute::StackProtect); break;
     case lltok::kw_sspreq:            B.addAttribute(Attribute::StackProtectReq); break;
     case lltok::kw_sspstrong:         B.addAttribute(Attribute::StackProtectStrong); break;
+    case lltok::kw_safestack:         B.addAttribute(Attribute::SafeStack); break;
     case lltok::kw_sanitize_address:  B.addAttribute(Attribute::SanitizeAddress); break;
     case lltok::kw_sanitize_thread:   B.addAttribute(Attribute::SanitizeThread); break;
     case lltok::kw_sanitize_memory:   B.addAttribute(Attribute::SanitizeMemory); break;
@@ -1267,6 +1268,7 @@ bool LLParser::ParseOptionalParamAttrs(AttrBuilder &B) {
     case lltok::kw_ssp:
     case lltok::kw_sspreq:
     case lltok::kw_sspstrong:
+    case lltok::kw_safestack:
     case lltok::kw_uwtable:
       HaveError |= Error(Lex.getLoc(), "invalid use of function-only attribute");
       break;
@@ -1343,6 +1345,7 @@ bool LLParser::ParseOptionalReturnAttrs(AttrBuilder &B) {
     case lltok::kw_ssp:
     case lltok::kw_sspreq:
     case lltok::kw_sspstrong:
+    case lltok::kw_safestack:
     case lltok::kw_uwtable:
       HaveError |= Error(Lex.getLoc(), "invalid use of function-only attribute");
       break;

diff --git a/lib/AsmParser/LLToken.h b/lib/AsmParser/LLToken.h
@@ -135,6 +135,7 @@ namespace lltok {
     kw_ssp,
     kw_sspreq,
     kw_sspstrong,
+    kw_safestack,
     kw_sret,
     kw_sanitize_thread,
     kw_sanitize_memory,

diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1146,6 +1146,8 @@ static Attribute::AttrKind getAttrFromCode(uint64_t Code) {
     return Attribute::StackProtectReq;
   case bitc::ATTR_KIND_STACK_PROTECT_STRONG:
     return Attribute::StackProtectStrong;
+  case bitc::ATTR_KIND_SAFESTACK:
+    return Attribute::SafeStack;
   case bitc::ATTR_KIND_STRUCT_RET:
     return Attribute::StructRet;
   case bitc::ATTR_KIND_SANITIZE_ADDRESS:

diff --git a/lib/Bitcode/Writer/BitcodeWriter.cpp b/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -232,6 +232,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_STACK_PROTECT_REQ;
   case Attribute::StackProtectStrong:
     return bitc::ATTR_KIND_STACK_PROTECT_STRONG;
+  case Attribute::SafeStack:
+    return bitc::ATTR_KIND_SAFESTACK;
   case Attribute::StructRet:
     return bitc::ATTR_KIND_STRUCT_RET;
   case Attribute::SanitizeAddress:

diff --git a/lib/CodeGen/LLVMBuild.txt b/lib/CodeGen/LLVMBuild.txt
@@ -22,4 +22,4 @@ subdirectories = AsmPrinter SelectionDAG MIRParser
 type = Library
 name = CodeGen
 parent = Libraries
-required_libraries = Analysis Core MC Scalar Support Target TransformUtils
+required_libraries = Analysis Core Instrumentation MC Scalar Support Target TransformUtils
diff --git a/lib/CodeGen/Passes.cpp b/lib/CodeGen/Passes.cpp
@@ -24,6 +24,7 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Instrumentation.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils/SymbolRewriter.h"
 
@@ -456,6 +457,9 @@ void TargetPassConfig::addCodeGenPrepare() {
 void TargetPassConfig::addISelPrepare() {
   addPreISel();
 
+  // Add both the safe stack and the stack protection passes: each of them will
+  // only protect functions that have corresponding attributes.
+  addPass(createSafeStackPass());
   addPass(createStackProtectorPass(TM));
 
   if (PrintISelInput)

diff --git a/lib/IR/Attributes.cpp b/lib/IR/Attributes.cpp
@@ -252,6 +252,8 @@ std::string Attribute::getAsString(bool InAttrGrp) const {
     return "sspreq";
   if (hasAttribute(Attribute::StackProtectStrong))
     return "sspstrong";
+  if (hasAttribute(Attribute::SafeStack))
+    return "safestack";
   if (hasAttribute(Attribute::StructRet))
     return "sret";
   if (hasAttribute(Attribute::SanitizeThread))
@@ -437,6 +439,7 @@ uint64_t AttributeImpl::getAttrMask(Attribute::AttrKind Val) {
   case Attribute::NonNull:         return 1ULL << 44;
   case Attribute::JumpTable:       return 1ULL << 45;
   case Attribute::Convergent:      return 1ULL << 46;
+  case Attribute::SafeStack:       return 1ULL << 47;
   case Attribute::Dereferenceable:
     llvm_unreachable("dereferenceable attribute not supported in raw format");
     break;

diff --git a/lib/IR/Verifier.cpp b/lib/IR/Verifier.cpp
@@ -1251,6 +1251,7 @@ void Verifier::VerifyAttributeTypes(AttributeSet Attrs, unsigned Idx,
         I->getKindAsEnum() == Attribute::StackProtect ||
         I->getKindAsEnum() == Attribute::StackProtectReq ||
         I->getKindAsEnum() == Attribute::StackProtectStrong ||
+        I->getKindAsEnum() == Attribute::SafeStack ||
         I->getKindAsEnum() == Attribute::NoRedZone ||
         I->getKindAsEnum() == Attribute::NoImplicitFloat ||
         I->getKindAsEnum() == Attribute::Naked ||

diff --git a/lib/Target/CppBackend/CPPBackend.cpp b/lib/Target/CppBackend/CPPBackend.cpp
@@ -513,6 +513,7 @@ void CppWriter::printAttributes(const AttributeSet &PAL,
       HANDLE_ATTR(StackProtect);
       HANDLE_ATTR(StackProtectReq);
       HANDLE_ATTR(StackProtectStrong);
+      HANDLE_ATTR(SafeStack);
       HANDLE_ATTR(NoCapture);
       HANDLE_ATTR(NoRedZone);
       HANDLE_ATTR(NoImplicitFloat);

diff --git a/lib/Transforms/IPO/Inliner.cpp b/lib/Transforms/IPO/Inliner.cpp
@@ -93,19 +93,26 @@ static void AdjustCallerSSPLevel(Function *Caller, Function *Callee) {
   // clutter to the IR.
   AttrBuilder B;
   B.addAttribute(Attribute::StackProtect)
-    .addAttribute(Attribute::StackProtectStrong);
+    .addAttribute(Attribute::StackProtectStrong)
+    .addAttribute(Attribute::StackProtectReq);
   AttributeSet OldSSPAttr = AttributeSet::get(Caller->getContext(),
                                               AttributeSet::FunctionIndex,
                                               B);
 
-  if (Callee->hasFnAttribute(Attribute::StackProtectReq)) {
+  if (Callee->hasFnAttribute(Attribute::SafeStack)) {
+    Caller->removeAttributes(AttributeSet::FunctionIndex, OldSSPAttr);
+    Caller->addFnAttr(Attribute::SafeStack);
+  } else if (Callee->hasFnAttribute(Attribute::StackProtectReq) &&
+             !Caller->hasFnAttribute(Attribute::SafeStack)) {
     Caller->removeAttributes(AttributeSet::FunctionIndex, OldSSPAttr);
     Caller->addFnAttr(Attribute::StackProtectReq);
   } else if (Callee->hasFnAttribute(Attribute::StackProtectStrong) &&
+             !Caller->hasFnAttribute(Attribute::SafeStack) &&
              !Caller->hasFnAttribute(Attribute::StackProtectReq)) {
     Caller->removeAttributes(AttributeSet::FunctionIndex, OldSSPAttr);
     Caller->addFnAttr(Attribute::StackProtectStrong);
   } else if (Callee->hasFnAttribute(Attribute::StackProtect) &&
+             !Caller->hasFnAttribute(Attribute::SafeStack) &&
              !Caller->hasFnAttribute(Attribute::StackProtectReq) &&
              !Caller->hasFnAttribute(Attribute::StackProtectStrong))
     Caller->addFnAttr(Attribute::StackProtect);

diff --git a/lib/Transforms/Instrumentation/CMakeLists.txt b/lib/Transforms/Instrumentation/CMakeLists.txt
@@ -6,6 +6,7 @@ add_llvm_library(LLVMInstrumentation
   MemorySanitizer.cpp
   Instrumentation.cpp
   InstrProfiling.cpp
+  SafeStack.cpp
   SanitizerCoverage.cpp
   ThreadSanitizer.cpp
 

diff --git a/lib/Transforms/Instrumentation/Instrumentation.cpp b/lib/Transforms/Instrumentation/Instrumentation.cpp
@@ -30,6 +30,7 @@ void llvm::initializeInstrumentation(PassRegistry &Registry) {
   initializeThreadSanitizerPass(Registry);
   initializeSanitizerCoverageModulePass(Registry);
   initializeDataFlowSanitizerPass(Registry);
+  initializeSafeStackPass(Registry);
 }
 
 /// LLVMInitializeInstrumentation - C binding for