Undefined Behavior and Compiler Optimizations (NDC Oslo 2018)
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This document summarizes Patricia Aas' presentation on secure programming practices in C++. It introduces Patricia and her background programming mainly in C++. The presentation covers topics like undefined behavior, compiler optimizations, and examples of insecure code. It provides code samples to demonstrate undefined behavior and how compilers can remove code meant to clear buffers due to optimizations. It recommends using functions like memset_s or SecureZeroMemory to clear sensitive information instead.
![Infinite Loop (Undefined Behavior)
#include <iostream>
#include <complex>
using namespace std;
int main(void) {
complex<int> delta;
complex<int> mc[4] = {0};
for(int di = 0; di < 4; di++, delta = mc[di]) {
cout << di << endl;
}
}
@pati_gallardo
(Thanks to @shafikyaghmour) https://stackoverflow.com/questions/32506643/c-compilation-bug
Undefined
Behavior!](https://image.slidesharecdn.com/undefinedbehaviorandcompileroptimizationsndcoslo2018-180615132215/85/Undefined-Behavior-and-Compiler-Optimizations-NDC-Oslo-2018-8-320.jpg)
![0) CWE-14: Compiler Removal of Code to Clear Buffers
void GetData(char *MFAddr) {
char pwd[64];
if (GetPasswordFromUser(pwd, sizeof(pwd))) {
if (ConnectToMainframe(MFAddr, pwd)) {
// Interaction with mainframe
}
}
memset(pwd, 0, sizeof(pwd)); // <- Removed by the optimizer
}
@pati_gallardo
SEI: MSC06-C. Beware of compiler optimizations
SEI: MEM03-C. Clear sensitive information stored in reusable resources](https://image.slidesharecdn.com/undefinedbehaviorandcompileroptimizationsndcoslo2018-180615132215/85/Undefined-Behavior-and-Compiler-Optimizations-NDC-Oslo-2018-12-320.jpg)
Undefined Behavior and Compiler Optimizations (NDC Oslo 2018)
- 2. Secure Programming Practices in C++ @pati_gallardo Patricia Aas NDC { Oslo } 2018
- 3. Patricia Aas - Vivaldi Browser Programmer - mainly in C++ Currently : Vivaldi Technologies Previously : Cisco Systems, Knowit, Opera Software Master in Computer Science Twitter : @pati_gallardo Photos: pixabay.com - CC0
- 6. undefined behavior “Examples of undefined behavior are memory accesses outside of array bounds, signed integer overflow, null pointer dereference, modification of the same scalar more than once in an expression without sequence points, access to an object through a pointer of a different type, etc. Compilers are not required to diagnose undefined behavior (although many simple situations are diagnosed), and the compiled program is not required to do anything meaningful.” http://en.cppreference.com/w/cpp/language/ub @pati_gallardo
- 7. - Don’t reason about undefined behaviour - Assume that it crashes or is never executed - Changing compiler, compiler version or optimization level can break your application Undefined Behaviour
- 8. Infinite Loop (Undefined Behavior) #include <iostream> #include <complex> using namespace std; int main(void) { complex<int> delta; complex<int> mc[4] = {0}; for(int di = 0; di < 4; di++, delta = mc[di]) { cout << di << endl; } } @pati_gallardo (Thanks to @shafikyaghmour) https://stackoverflow.com/questions/32506643/c-compilation-bug Undefined Behavior!
- 9. Infinite Loop (Undefined Behavior) Can we run it? https://godbolt.org/g/TDjM8h @pati_gallardo (Thanks to @shafikyaghmour) https://stackoverflow.com/questions/32506643/c-compilation-bug
- 11. @pati_gallardo The Case Of The Disappearing Memset
- 12. 0) CWE-14: Compiler Removal of Code to Clear Buffers void GetData(char *MFAddr) { char pwd[64]; if (GetPasswordFromUser(pwd, sizeof(pwd))) { if (ConnectToMainframe(MFAddr, pwd)) { // Interaction with mainframe } } memset(pwd, 0, sizeof(pwd)); // <- Removed by the optimizer } @pati_gallardo SEI: MSC06-C. Beware of compiler optimizations SEI: MEM03-C. Clear sensitive information stored in reusable resources
- 13. 0) CWE-14: Compiler Removal of Code to Clear Buffers Should we Godbolt this? https://godbolt.org/g/FpEsht @pati_gallardo SEI: MSC06-C. Beware of compiler optimizations SEI: MEM03-C. Clear sensitive information stored in reusable resources
- 14. Memset_s : Zeroing Memory // Compliant Solution (C11) memset_s(pwd, 0, sizeof(pwd)); // Windows Solution SecureZeroMemory(pwd, sizeof(pwd)); @pati_gallardo SEI: MSC06-C. Beware of compiler optimizations SEI: MEM03-C. Clear sensitive information stored in reusable resources
- 15. Code is on GitHub: https://github.com/patricia-gallardo/insecure-coding-examples @pati_gallardo
- 16. @pati_gallardo