zhangyang-variable-monitor/source/module/monitor_mem.c

#include "monitor_mem.h"

#include <linux/highmem.h> // for FOLL_FORCE
#include <linux/sched.h>   // pid  pid_task
#include <linux/slab.h>    /*  for kmalloc */
#include <linux/sched/mm.h> // get_task_mm

/// @brief transfer user space address to kernel space address
///        change static global "kaddr" and "page" value
/// @param pid: process id
/// @param kaddr: user space address
/// @return kernel space address + offset
void *convert_user_space_ptr(pid_t pid, unsigned long addr) {
  struct task_struct *task;
  struct mm_struct *mm;
  int ret;

  // unsigned long aligned_addr = 0;
  // unsigned long offset = 0;

  watch_local_memory *node;

  // if (addr < TASK_SIZE || addr > -PAGE_SIZE)
  // {
  //     printk(KERN_ERR "Invalid address\n");
  //     return NULL;
  // }

  // for get_user_pages_remote
  unsigned long aligned_addr = addr & PAGE_MASK;
  unsigned long offset = addr & ~PAGE_MASK;

  printk(KERN_INFO "%s\n", __FUNCTION__);

  node = kmalloc(sizeof(watch_local_memory), GFP_KERNEL);
  node->task_id = pid;

  // Find the task with pid
  rcu_read_lock();
  task = pid_task(find_vpid(pid), PIDTYPE_PID);
  rcu_read_unlock();

  if (!task) {
    printk(KERN_ERR "Cannot find task for PID %d\n", pid);
    kfree(node); // careful there is kfree
    return NULL;
  }
  // Get memory descriptor
  mm = get_task_mm(task);
  if (!mm) {
    printk(KERN_ERR "Cannot get memory descriptor\n");
    kfree(node); // careful there is kfree
    return NULL;
  }
  down_read(&task->mm->mmap_lock);
  ret = get_user_pages_remote(task->mm, aligned_addr, 1, FOLL_FORCE,
                              &(node->page), NULL, NULL);
  up_read(&task->mm->mmap_lock);

  if (ret != 1) {
    printk(KERN_ERR "Cannot get user page\n");
    kfree(node); // careful there is kfree
    return NULL;
  }
  // Map the page to kernel space
  node->kaddr = kmap(node->page);
  list_add_tail(&node->entry, &watch_local_memory_list); // add to list
  // printk(KERN_INFO "node->kaddr: %p, aligned_addr: %ld, offset: %ld\n",
  // node->kaddr, aligned_addr, offset);
  return (void *)((unsigned long)(node->kaddr) + offset);
}

/// @brief free page in watch_local_memory_list with task_id
/// @param task_id
void free_page_list(pid_t task_id) {
  watch_local_memory *node, *next;
  list_for_each_entry_safe(node, next, &watch_local_memory_list, entry) {
    if (node == NULL)
      break;
    if (node->task_id == task_id) {
      // unmap and release the page
      if (node->kaddr)
        kunmap(node->kaddr);
      if (node->page)
        put_page(node->page);
      list_del(&node->entry);
      kfree(node); // careful there is kfree
    }
  }
}

/// @brief free all page in watch_local_memory_list
/// @param
void free_all_page_list(void) {
  watch_local_memory *node, *next;
  list_for_each_entry_safe(node, next, &watch_local_memory_list, entry) {
    if (node == NULL)
      break;
    // unmap and release the page
    if (node->kaddr)
      kunmap(node->kaddr);
    if (node->page)
      put_page(node->page);
    list_del(&node->entry);
    kfree(node); // careful there is kfree
  }
}

// for read_and_compare
typedef unsigned char (*compare_func)(void *, long long);

unsigned char compare_1_byte_signed(void *ptr, long long threshold) {
  // printk("compare_1_byte_signed: value %d, biss: %lld\n", *(char *)ptr,
  // threshold);
  return *(char *)ptr > threshold;
}
unsigned char compare_1_byte_unsigned(void *ptr, long long threshold) {
  // printk("compare_1_byte_unsigned: value %d, biss: %lld\n", *(unsigned char
  // *)ptr, threshold);
  return *(unsigned char *)ptr > threshold;
}
unsigned char compare_2_byte_signed(void *ptr, long long threshold) {
  // printk("compare_2_byte_signed: value %d, biss: %lld\n", *(short int *)ptr,
  // threshold);
  return *(short int *)ptr > threshold;
}
unsigned char compare_2_byte_unsigned(void *ptr, long long threshold) {
  // printk("compare_2_byte_unsigned: value %d, biss: %lld\n", *(unsigned short
  // int *)ptr, threshold);
  return *(unsigned short int *)ptr > threshold;
}
unsigned char compare_4_byte_signed(void *ptr, long long threshold) {
  // printk("compare_4_byte_signed: value %d, biss: %lld\n", *(int *)ptr,
  // threshold);
  return *(int *)ptr > threshold;
}
unsigned char compare_4_byte_unsigned(void *ptr, long long threshold) {
  // printk("compare_4_byte_unsigned: value %d, biss: %lld\n", *(unsigned int
  // *)ptr, threshold);
  return *(unsigned int *)ptr > threshold;
}
unsigned char compare_8_byte_signed(void *ptr, long long threshold) {
  // printk("compare_8_byte_signed: value %lld, biss: %lld\n", *(long long
  // *)ptr, threshold);
  return *(long long *)ptr > threshold;
}
unsigned char compare_8_byte_unsigned(void *ptr, long long threshold) {
  // printk("compare_8_byte_unsigned: value %lld, biss: %lld\n", *(unsigned long
  // long *)ptr, threshold);
  return *(unsigned long long *)ptr > threshold;
}
// list of compare functions
static compare_func compare_funcs[8] = {
    compare_1_byte_signed,   compare_2_byte_signed,   compare_4_byte_signed,
    compare_8_byte_signed,   compare_1_byte_unsigned, compare_2_byte_unsigned,
    compare_4_byte_unsigned, compare_8_byte_unsigned};

static int func_indices[2][9] = {{0, 0, 1, 0, 2, 0, 0, 0, 3},
                                 {0, 4, 5, 0, 6, 0, 0, 0, 7}};

/// @brief read k_arg->kptr and compare with threshold
/// @param k_arg
/// @return result of compare
unsigned char read_and_compare(void *ptr, int len, unsigned char greater_flag,
                               unsigned char is_unsigned, long long threshold) {
  unsigned char result = 0;

  // if (len != 1 && len != 2 && len != 4 && len != 8)
  // {
  //     printk(KERN_ERR "Invalid length\n");
  //     return 0;
  // }

  result = compare_funcs[func_indices[is_unsigned][len]](ptr, threshold);

  // printk(KERN_INFO "read_and_compare: name %s, value %d, biss: %lld, result:
  // %d \n", k_arg->name, *(int *)ptr,
  //        threshold, result);

  if (greater_flag)
    return result;
  else
    return !result;
}