转自：https://blog.csdn.net/thisinnocence/article/details/80414008

之前的一篇文章: Linux C/C++内存越界定位: 利用mprotect使程序在crash在第一现场。里面没有用malloc来申请按页对齐的内存，其实也可以适配malloc，多申请2页，取中间按照页对齐的内存使用。使用malloc，可以使得进程的地址空间布局不会相对原来发生太大变化。代码如下：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

struct mem_align {
    void *origin_start;  // for free
    void *start;         // data addr start, align page size
    void *end;           // data addr end,   align page size
    void *origin_end;
};

int malloc_align_page(size_t memsize, struct mem_align *mem)
{
    if (memsize == 0 || mem == NULL)
        return -1;

    memset(mem, 0, sizeof(*mem));
    long pagesize = sysconf(_SC_PAGE_SIZE);
    if (pagesize == -1) {
        perror("sysconf err");
        return -1;
    }

    size_t datasize = memsize + pagesize * 2;
    mem->origin_start = malloc(datasize);
    if(mem->origin_start == NULL)
        return -1;
    mem->origin_end = mem->origin_start + datasize;

    long mask = pagesize - 1;
    mem->start = (void *)((long)(mem->origin_start + pagesize) & ~mask);
    long pagenum = memsize / pagesize + 1;
    mem->end = mem->start + pagesize * pagenum;
    return 0;
}

int main()
{
    int ret;
    struct mem_align mem;

    ret = malloc_align_page(1024, &mem);
    if (ret != 0) {
        return ret;
    }

    ret = mprotect(mem.start, (size_t)(mem.end - mem.start), PROT_READ);
    if (ret == -1) {
        perror("mportect");
        return ret;
    }

    sleep(600); // 让进程先挂起不退出，看/proc/[pid]/maps里的地址空间对应页的权限
    // free(mem.origin_start);
    return 0;
}

一组运行结果如下：

root@ubuntu:/media/psf/Home/iLearn/learn_c/mprotect# ./a.out
malloc mem: 0xbab010 - 0xbad410
align page: 0xbac000 - 0xbad000

root@ubuntu:~# ps -ef|grep a.out
root      1429 32072  0 00:24 pts/11   00:00:00 ./a.out
root      1718  1153  0 00:25 pts/17   00:00:00 grep --color=auto a.out
root@ubuntu:~# grep bac00 /proc/1429/maps -C 3
00400000-00401000 r-xp 00000000 00:18 53150451                           /media/psf/Home/iLearn/learn_c/mprotect/a.out
00600000-00601000 r--p 00000000 00:18 53150451                           /media/psf/Home/iLearn/learn_c/mprotect/a.out
00601000-00602000 rw-p 00001000 00:18 53150451                           /media/psf/Home/iLearn/learn_c/mprotect/a.out
00bab000-00bac000 rw-p 00000000 00:00 0                                  [heap]
00bac000-00bad000 r--p 00000000 00:00 0                                  [heap]  # 这块对内存页已经被改成了只读权限
00bad000-00bce000 rw-p 00000000 00:00 0                                  [heap]
7f657e6b3000-7f657e86f000 r-xp 00000000 08:01 397412                     /lib/x86_64-linux-gnu/libc-2.19.so
7f657e86f000-7f657ea6e000 ---p 001bc000 08:01 397412                     /lib/x86_64-linux-gnu/libc-2.19.so