move off rand-selfmod

1 files changed, 108 insertions, 0 deletions

diff --git a/starts/random-selfmod/random.cpp b/starts/random-selfmod/random.cpp
new file mode 100644
index 0000000..afdf4c7
--- /dev/null
+++ b/starts/random-selfmod/random.cpp
@@ -0,0 +1,108 @@
+// let's try to make it very simple
+
+#include <fcntl.h>
+#include <signal.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+// 1. write a function to randomly put data in a buffer
+// 		[apparently one loaded from a file]
+
+#define MAPFNAME "random.bin"
+
+pid_t child = 0;
+bool child_terminated = false;
+void handleSigChld(int)
+{
+	child_terminated = true;
+}
+
+static unsigned long long * count;
+
+void random(int mapfd, int randfd, void *addr)
+{
+	pid_t pid = getpid();
+
+	// *count is shared and stored
+	for (*count = 0; ; ++ *count) {
+		unsigned long long old_count = *count;
+
+		// if successful child, update & kill parent
+		if (getpid() != pid) {
+			msync(addr + pos, size, MS_SYNC | MS_INVALIDATE);
+
+			kill(pid, SIGTERM);
+			pid = getpid();
+
+			// add data to git.
+			system("git add " MAPFNAME);
+			system("git commit -m selfmod");
+		}
+		
+		// handle crashes with fork()
+		child = fork();
+		if (child == 0) {
+			// we are new child process
+			// self-modify by 1-8 bytes
+			uint16_t pos;
+			uint8_t size;
+			read(randfd, &pos, sizeof(pos));
+			read(randfd, &size, sizeof(size));
+			size = (size & 0x7) + 1; // self-modify by 1-8 bytes
+			read(randfd, addr + pos, size);
+			// loop
+		} else {
+			// old process: make sure new process succeeds within 1s
+			time_t then = time(0);
+			for (;;) {
+				if (child_terminated || time(0) > then) {
+					// child did not succeed
+					kill(child, SIGTERM);
+					child_terminated = false;
+					// try again
+					break;
+				}
+				if (old_count < *count + 1) {
+					// incremented count by 1: success; hand off to child
+					return;
+				}
+			}
+		}
+	}
+}
+
+void random_tail() {
+}
+
+void main()
+{
+	// handle SIGCHLD by setting a global flag
+	struct sigaction sigchld;
+	sigchld.sa_handler = handleSigChld;
+	sigchld.sa_flags = SA_NOCLDWAIT;
+	sigaction(SIGCHLD, &sigchld, NULL);
+
+	int fd = open(MAPFNAME, O_RDWR);
+	if (fd == -1 && errno == ENOENT) {
+		// does not exist yet
+		fd = open("random.bin", O_RDWR | O_CREAT);
+		// 2. seed the buffer with the function that puts random data in it
+		count = 0;
+		write(fd, &count, sizeof(count));
+		write(fd, &random, &random_tail - &random);
+	}
+
+	int randfd = open("/dev/random", O_RDONLY);
+
+	// a buffer of 1 gig working space; random data will fill it
+	void *buf = mmap(NULL,
+	                 0x40000000,
+	                 PROT_EXEC | PROT_READ | PROT_WRITE,
+	                 MAP_SHARED | MAP_32BIT,
+	                 fd,
+	                 0;
+
+	// 3. execute the buffer
+	void (*buf_as_func)(void*) = (void*)((uint8_t*)buf + count);
+	buf_as_func(mapfname, mapfd, randfd, buf);
+}