如何从程序访问控制寄存器 cr0,cr2,cr3?获取分段错误

问题描述

我编写了一个程序，试图读取和写入控制寄存器.

I have written a program which tries to read from and write to the control registers.

程序编译正常，但是当内联汇编即将执行时，它产生了一个分段错误.

The program compiles fine, but when the inline assembly is about to be executed, it produces a segmentation fault.

代码:

void instructions(int val)
{
    int i;
    int value;
    for(i = 0; i < val; i++)
         __asm__("mov %cr0, %eax");
}

我使用 GDB 并通过每条装配线，在 mov %cr0,%eax 上发生了分段错误.

I used GDB and stepped through each assembly line and it is on the mov %cr0,%eax that the segmentation fault is occurring.

谁知道哪里出了问题?

推荐答案

引用自 英特尔® 64 和 IA-32 架构软件开发人员手册 3-650 卷.2A 关于移入和移出控制寄存器:

Quoting from Intel® 64 and IA-32 Architectures Software Developer Manuals 3-650 Vol. 2A on moving to and from control registers:

该指令只有在当前权限级别为0时才能执行.

这意味着指令只能在内核模式下执行.

Which means the instruction can only be executed in kernel mode.

记录 cr0、cr2 和 cr3 内容的最小内核模块可能如下所示(32 位代码路径未经测试):

A minimal kernel module, that logs the contents of cr0, cr2 and cr3 could look something like this (32-bit code path untested):

/* hello.c */
#include <linux/module.h>
#include <linux/kernel.h>

int init_module(void)
{
#ifdef __x86_64__
    u64 cr0, cr2, cr3;
    __asm__ __volatile__ (
        "mov %%cr0, %%rax
	"
        "mov %%eax, %0
	"
        "mov %%cr2, %%rax
	"
        "mov %%eax, %1
	"
        "mov %%cr3, %%rax
	"
        "mov %%eax, %2
	"
    : "=m" (cr0), "=m" (cr2), "=m" (cr3)
    : /* no input */
    : "%rax"
    );
#elif defined(__i386__)
    u32 cr0, cr2, cr3;
    __asm__ __volatile__ (
        "mov %%cr0, %%eax
	"
        "mov %%eax, %0
	"
        "mov %%cr2, %%eax
	"
        "mov %%eax, %1
	"
        "mov %%cr3, %%eax
	"
        "mov %%eax, %2
	"
    : "=m" (cr0), "=m" (cr2), "=m" (cr3)
    : /* no input */
    : "%eax"
    );
#endif
    printk(KERN_INFO "cr0 = 0x%8.8X
", cr0);
    printk(KERN_INFO "cr2 = 0x%8.8X
", cr2);
    printk(KERN_INFO "cr3 = 0x%8.8X
", cr3);
    return 0;
}

void cleanup_module(void)
{
}

# Makefile

obj-m += hello.o

all:
    make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
    make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

test: all
    sudo insmod ./hello.ko
    sudo rmmod hello
    dmesg | tail

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