我是内核编程的新手，我找不到足够的信息来了解为什么会发生这种情况。基本上，我试图用一些简单的方法来替换内核 IDT 中的页面错误处理程序，最终调用原始处理程序。我只想让这个函数打印一个它被调用的通知，并且printk()在它内部调用总是会导致内核恐慌。否则它运行良好。
#include <asm/desc.h>
#include <linux/mm.h>
#include <asm/traps.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <asm/uaccess.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <asm/desc_defs.h>
#include <linux/moduleparam.h>
#define PAGEFAULT_INDEX 14
// Old and new IDT registers
static struct desc_ptr old_idt_reg, new_idt_reg;
static __attribute__((__used__)) unsigned long old_pagefault_pointer, new_page;
// The function that replaces the original handler
asmlinkage void isr_pagefault(void);
asm(" .text");
asm(" .type isr_pagefault,@function");
asm("isr_pagefault:");
asm(" callq print_something");
asm(" jmp *old_pagefault_pointer");
void print_something(void) {
// This printk causes the kernel to crash!
printk(KERN_ALERT "Page fault handler called\n");
return;
}
void my_idt_load(void *ptr) {
printk(KERN_ALERT "Loading on a new processor...\n");
load_idt((struct desc_ptr*)ptr);
return;
}
int module_begin(void) {
gate_desc *old_idt_addr, *new_idt_addr;
unsigned long idt_length;
store_idt(&old_idt_reg);
old_idt_addr = (gate_desc*)old_idt_reg.address;
idt_length = old_idt_reg.size;
// Get the pagefault handler pointer from the IDT's pagefault entry
old_pagefault_pointer = 0
| ((unsigned long)(old_idt_addr[PAGEFAULT_INDEX].offset_high) << 32 )
| ((unsigned long)(old_idt_addr[PAGEFAULT_INDEX].offset_middle) << 16 )
| ((unsigned long)(old_idt_addr[PAGEFAULT_INDEX].offset_low) );
printk(KERN_ALERT "Saved pointer to old pagefault handler: %p\n", (void*)old_pagefault_pointer);
// Allocate a new page for the new IDT
new_page = __get_free_page(GFP_KERNEL);
if (!new_page)
return -1;
// Copy the original IDT to the new page
memcpy((void*)new_page, old_idt_addr, idt_length);
// Set up the new IDT
new_idt_reg.address = new_idt_addr = new_page;
new_idt_reg.size = idt_length;
pack_gate(
&new_idt_addr[PAGEFAULT_INDEX],
GATE_INTERRUPT,
(unsigned long)isr_pagefault, // The interrupt written in assembly at the start of the code
0, 0, __KERNEL_CS
);
// Load the new table
load_idt(&new_idt_reg);
smp_call_function(my_idt_load, (void*)&new_idt_reg, 1); // Call load_idt on the rest of the cores
printk(KERN_ALERT "New IDT loaded\n\n");
return 0;
}
void module_end(void) {
printk( KERN_ALERT "Exit handler called now. Reverting changes and exiting...\n\n");
load_idt(&old_idt_reg);
smp_call_function(my_idt_load, (void*)&old_idt_reg, 1);
if (new_page)
free_page(new_page);
}
module_init(module_begin);
module_exit(module_end);
非常感谢任何可以告诉我我在这里做错了什么的人。
