implement thread register read and write. needs more testing

include/process.h

@@ -2,6 +2,7 @@
 #define __PROCESS_H
 
 #include <sys/types.h>
+#include <sys/user.h>
 
 typedef enum {
     UNINTERRUPTABLE_SLEEP   = 'D',
@@ -61,4 +62,10 @@ int process_attach_all(process_status_t* threads, size_t thread_count);
 // detaches from all threads
 void process_detach_all(process_status_t* threads, size_t thread_count);
 
+// read registers of thread. returns 0 on success, 1 on error
+int process_read_registers(process_status_t* thread, struct user_regs_struct* regs);
+
+// write registers for thread. for return value same rules apply as read registers function
+int process_write_registers(process_status_t* thread, const struct user_regs_struct* regs);
+
 #endif

src/main.c

@@ -3,6 +3,7 @@
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdint.h>
 #include <string.h>
 #include "process.h"
 
@@ -89,8 +90,17 @@ int main(int argc, char** argv)
         return 1;
     }
     
-    puts("attached to all threads. press any key");
+    puts("attached to all threads. please enter address of destination");
-    getc(stdin);
+    void* destination;
+    scanf("%p", &destination);
+
+    struct user_regs_struct regs;
+    if (process_read_registers(active, &regs))
+        fprintf(stderr, "failed to read registers: %s\n", strerror(errno));
+    // hijack instruction pointer to our destination
+    regs.rip = (uintptr_t)destination;
+    if (process_write_registers(active, &regs))
+        fprintf(stderr, "failed to write registers: %s\n", strerror(errno));
 
     process_detach_all(threads, thread_count);
     

src/process.c

@@ -4,6 +4,8 @@
 #include <sys/capability.h>
 #include <sys/ptrace.h>
 #include <sys/wait.h>
+#include <sys/uio.h>
+#include <linux/elf.h>
 #include <unistd.h>
 #include <fcntl.h>
 #include <dirent.h>
@@ -278,4 +280,25 @@ int process_attach_all(process_status_t* threads, size_t thread_count)
 void process_detach_all(process_status_t* threads, size_t thread_count)
 {
     while (thread_count--) ptrace(PTRACE_DETACH, threads[thread_count].pid, NULL, NULL);
+}
+
+int process_read_registers(process_status_t* thread, struct user_regs_struct* regs)
+{
+    struct iovec data = {
+        .iov_base = regs,
+        .iov_len = sizeof(struct user_regs_struct)
+    };
+    memset(regs, '\0', sizeof(struct user_regs_struct));
+
+    return ptrace(PTRACE_GETREGSET, thread->pid, NT_PRSTATUS, &data) < 0;
+}
+
+int process_write_registers(process_status_t* thread, const struct user_regs_struct* regs)
+{
+    struct iovec data = {
+        .iov_base = (void*)regs,
+        .iov_len = sizeof(struct user_regs_struct)
+    };
+
+    return ptrace(PTRACE_SETREGSET, thread->pid, NT_PRSTATUS, &data) < 0;
 }