Data update

Task/Machine-code/Common-Lisp/machine-code.lisp

@@ -1,3 +1,49 @@
+;;Update 2024: the previous code is likely not going to work on modern OS, because there is a need to allocate memory with the correct permissions (readable, writable, and executable). We will update with another machine code, equivalent to the function 'ash' in common lisp
+
+89 f8                	mov    %edi,%eax
+89 f1                	mov    %esi,%ecx
+d3 e8                	shr    %cl,%eax
+c3                   	ret
+
+;;sbcl
+(require :sb-posix)
+
+(defconstant +PROT-READ+  1)
+(defconstant +PROT-WRITE+ 2)
+(defconstant +PROT-EXEC+  4)
+(defconstant +MAP-PRIVATE+ 2)
+(defconstant +MAP-ANONYMOUS+ #x20)
+
+(defun allocate-executable-memory (size)
+  (sb-posix:mmap nil
+                 size
+                 (logior +PROT-READ+ +PROT-WRITE+ +PROT-EXEC+)
+                 (logior +MAP-PRIVATE+ +MAP-ANONYMOUS+)
+                 -1
+                 0))
+
+;; Example usage:
+(defparameter *shellcode* #(#x89 #xf8 #x89 #xf1 #xd3 #xe8 #xc3))
+(defparameter *mem-ptr* (allocate-executable-memory (length *shellcode*)))
+
+;; Copy shellcode to allocated memory
+(loop for byte across *shellcode*
+      for i from 0
+      do (setf (sb-sys:sap-ref-8 *mem-ptr* i) byte))
+
+;; Create a callable function pointer
+(defparameter *func* (sb-alien:sap-alien *mem-ptr* (sb-alien:function sb-alien:unsigned-int sb-alien:unsigned-int sb-alien:unsigned-int)))
+
+;; Call the function
+(sb-alien:alien-funcall *func* 18 1)
+;; 9
+;;(ash 18 -1) => 9
+
+;; Don't forget to free the memory when done
+;;(sb-posix:munmap *mem-ptr* (length *shellcode*))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;old contribution starts here
 ;;Note that by using the 'CFFI' library, one can apply this procedure portably in any lisp implementation;
 ;; in this code however I chose to demonstrate only the implementation-dependent programs.