Self modifying code always segmentation faults on Linux
Solution 1:
You should to change memory access permissions in runtime.
#include <sys/mman.h>
void *addr = get_address_of_instruction_pointer();
int length = 4096; /* size of a page */
if (mprotect(addr, length, PROT_READ | PROT_WRITE | PROT_EXEC) == 0) {
/* current code page is now writable and code from it is allowed for execution */
}
Solution 2:
Modern CPUs have a feature called DEP which prevents execution of code on the stack. Previously, this was possible; now, it is not. The binary is loaded into read-only memory by default.
With that out of the way, you can use the mprotect system call to mark your binary's location in memory as executable - SO LONG AS YOUR CODE IS NOT DEP-PROTECTED. So don't try to put code and the stack and then jump into it.
Solution 3:
You can also disable write-protection for the entire program by passing the switch -N
to the linker. If you are invoking the linker from gcc, pass Wl,-N
. If you invoke ld
directly, pass -N
.