From ab03c1cdce90660dcb75d000ebda817ae589aaec Mon Sep 17 00:00:00 2001
From: Martin Nowack <martin.nowack@gmail.com>
Date: Sat, 5 May 2018 00:04:13 +0100
Subject: Fix handling of errno if external functions are invoked

If an external function in KLEE is invoked, it might update errno.
Previously, the errno specific variable in a state was only updated
if it was part of the executed instructions.
That opened up a timeframe that increased the likelihood of errno being
overwritten by another method call.

This patch fixes two issues:
* the errno of the KLEE process state is updated before the external
function call allowing to detect changes to it later on
* after the external call, the memory object of errno is directly
updated
with its new value, reducing the likelihood to be overwritten by
another
call

Additional features:
* Add support for `errno()` for Darwin as well.
* Simplified errno handling in POSIX layer
---
 lib/Core/ExternalDispatcher.cpp | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

(limited to 'lib/Core/ExternalDispatcher.cpp')

diff --git a/lib/Core/ExternalDispatcher.cpp b/lib/Core/ExternalDispatcher.cpp
index 6c54d34b..70c14050 100644
--- a/lib/Core/ExternalDispatcher.cpp
+++ b/lib/Core/ExternalDispatcher.cpp
@@ -65,6 +65,7 @@ private:
   llvm::Module *singleDispatchModule;
   std::vector<std::string> moduleIDs;
   std::string &getFreshModuleID();
+  int lastErrno;
 
 public:
   ExternalDispatcherImpl(llvm::LLVMContext &ctx);
@@ -72,6 +73,8 @@ public:
   bool executeCall(llvm::Function *function, llvm::Instruction *i,
                    uint64_t *args);
   void *resolveSymbol(const std::string &name);
+  int getLastErrno();
+  void setLastErrno(int newErrno);
 };
 
 std::string &ExternalDispatcherImpl::getFreshModuleID() {
@@ -114,7 +117,8 @@ void *ExternalDispatcherImpl::resolveSymbol(const std::string &name) {
   return addr;
 }
 
-ExternalDispatcherImpl::ExternalDispatcherImpl(LLVMContext &ctx) : ctx(ctx) {
+ExternalDispatcherImpl::ExternalDispatcherImpl(LLVMContext &ctx)
+    : ctx(ctx), lastErrno(0) {
   std::string error;
   singleDispatchModule = new Module(getFreshModuleID(), ctx);
 #if LLVM_VERSION_CODE < LLVM_VERSION(3, 6)
@@ -252,7 +256,10 @@ bool ExternalDispatcherImpl::runProtectedCall(Function *f, uint64_t *args) {
   if (setjmp(escapeCallJmpBuf)) {
     res = false;
   } else {
+    errno = lastErrno;
     executionEngine->runFunction(f, gvArgs);
+    // Explicitly acquire errno information
+    lastErrno = errno;
     res = true;
   }
 
@@ -346,6 +353,11 @@ Function *ExternalDispatcherImpl::createDispatcher(Function *target,
   return dispatcher;
 }
 
+int ExternalDispatcherImpl::getLastErrno() { return lastErrno; }
+void ExternalDispatcherImpl::setLastErrno(int newErrno) {
+  lastErrno = newErrno;
+}
+
 ExternalDispatcher::ExternalDispatcher(llvm::LLVMContext &ctx)
     : impl(new ExternalDispatcherImpl(ctx)) {}
 
@@ -359,4 +371,9 @@ bool ExternalDispatcher::executeCall(llvm::Function *function,
 void *ExternalDispatcher::resolveSymbol(const std::string &name) {
   return impl->resolveSymbol(name);
 }
+
+int ExternalDispatcher::getLastErrno() { return impl->getLastErrno(); }
+void ExternalDispatcher::setLastErrno(int newErrno) {
+  impl->setLastErrno(newErrno);
+}
 }
-- 
cgit 1.4.1