setup_nx.c

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#include <linux/spinlock.h>
#include <linux/errno.h>
#include <linux/init.h>

#include <asm/pgtable.h>
#include <asm/proto.h>

static int disable_nx __cpuinitdata;

/*
 * noexec = on|off
 *
 * Control non-executable mappings for processes.
 *
 * on      Enable
 * off     Disable
 */
static int __init noexec_setup(char *str)
{
    if (!str)
        return -EINVAL;
    if (!strncmp(str, "on", 2)) {
        disable_nx = 0;
    } else if (!strncmp(str, "off", 3)) {
        disable_nx = 1;
    }
    x86_configure_nx();
    return 0;
}
early_param("noexec", noexec_setup);

void __cpuinit x86_configure_nx(void)
{
    if (cpu_has_nx && !disable_nx)
        __supported_pte_mask |= _PAGE_NX;
    else
        __supported_pte_mask &= ~_PAGE_NX;
}

void __init x86_report_nx(void)
{
    if (!cpu_has_nx) {
        printk(KERN_NOTICE "Notice: NX (Execute Disable) protection "
               "missing in CPU!\n");
    } else {
#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
        if (disable_nx) {
            printk(KERN_INFO "NX (Execute Disable) protection: "
                   "disabled by kernel command line option\n");
        } else {
            printk(KERN_INFO "NX (Execute Disable) protection: "
                   "active\n");
        }
#else
        /* 32bit non-PAE kernel, NX cannot be used */
        printk(KERN_NOTICE "Notice: NX (Execute Disable) protection "
               "cannot be enabled: non-PAE kernel!\n");
#endif
    }
}