c++ - 强制页面边界段错误？

Question

我想编写一个测试(gcc 4.7)，在其中分配一页内存，该内存页位于我的进程不拥有的内存页的旁边，这样通过页面末尾的未对齐读取应该出现段错误.

这可能吗？我该怎么做？

Answer 1

您可以使用 mprotect使用 protection = PROT_NONE 使页面不可访问，例如

#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>

int main(void)
{
    char * a = valloc(4096 * 2);            // page-aligned memory allocation (two pages)

    int status = mprotect(&a[4096], 4096, PROT_NONE);
    if (status != 0) { perror("mprotect"); exit(1); }
                                            // protect second page

    for (int i = 0; i <= 4096; i += 256)    // test - should fail when i == 4096
    {
        printf("a[%d] = %u\n", i, a[i]);
    }

    return 0;
}

编译和测试:

$ gcc -Wall mprotect.c && ./a.out 
a[0] = 0
a[256] = 0
a[512] = 0
a[768] = 0
a[1024] = 0
a[1280] = 0
a[1536] = 0
a[1792] = 0
a[2048] = 0
a[2304] = 0
a[2560] = 0
a[2816] = 0
a[3072] = 0
a[3328] = 0
a[3584] = 0
a[3840] = 0
Bus error: 10
$ 

请注意，当我们尝试读取 a[4096] 时产生了一个总线错误。

如果你在 gdb 下运行它，你会得到更多信息:

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_PROTECTION_FAILURE at address: 0x0000000100803000
0x0000000100000eff in main () at mprotect.c:14
14          printf("a[%d] = %u\n", i, a[i]);