doublefault_32.c

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#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/init_task.h>
#include <linux/fs.h>

#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/processor.h>
#include <asm/desc.h>

#define DOUBLEFAULT_STACKSIZE (1024)
static unsigned long doublefault_stack[DOUBLEFAULT_STACKSIZE];
#define STACK_START (unsigned long)(doublefault_stack+DOUBLEFAULT_STACKSIZE)

#define ptr_ok(x) ((x) > PAGE_OFFSET && (x) < PAGE_OFFSET + MAXMEM)

static void doublefault_fn(void)
{
    struct desc_ptr gdt_desc = {0, 0};
    unsigned long gdt, tss;

    store_gdt(&gdt_desc);
    gdt = gdt_desc.address;

    printk(KERN_EMERG "PANIC: double fault, gdt at %08lx [%d bytes]\n", gdt, gdt_desc.size);

    if (ptr_ok(gdt)) {
        gdt += GDT_ENTRY_TSS << 3;
        tss = get_desc_base((struct desc_struct *)gdt);
        printk(KERN_EMERG "double fault, tss at %08lx\n", tss);

        if (ptr_ok(tss)) {
            struct x86_hw_tss *t = (struct x86_hw_tss *)tss;

            printk(KERN_EMERG "eip = %08lx, esp = %08lx\n",
                   t->ip, t->sp);

            printk(KERN_EMERG "eax = %08lx, ebx = %08lx, ecx = %08lx, edx = %08lx\n",
                t->ax, t->bx, t->cx, t->dx);
            printk(KERN_EMERG "esi = %08lx, edi = %08lx\n",
                t->si, t->di);
        }
    }

    for (;;)
        cpu_relax();
}

struct tss_struct doublefault_tss __cacheline_aligned = {
    .x86_tss = {
        .sp0        = STACK_START,
        .ss0        = __KERNEL_DS,
        .ldt        = 0,
        .io_bitmap_base = INVALID_IO_BITMAP_OFFSET,

        .ip     = (unsigned long) doublefault_fn,
        /* 0x2 bit is always set */
        .flags      = X86_EFLAGS_SF | 0x2,
        .sp     = STACK_START,
        .es     = __USER_DS,
        .cs     = __KERNEL_CS,
        .ss     = __KERNEL_DS,
        .ds     = __USER_DS,
        .fs     = __KERNEL_PERCPU,

        .__cr3      = __pa_nodebug(swapper_pg_dir),
    }
};