sysenter.c

/*
 * linux/arch/i386/kernel/sysenter.c
 *
 * (C) Copyright 2002 Linus Torvalds
 * Portions based on the vdso-randomization code from exec-shield:
 * Copyright(C) 2005-2006, Red Hat, Inc., Ingo Molnar
 *
 * This file contains the needed initializations to support sysenter.
 */

#include <linux/init.h>
#include <linux/smp.h>
#include <linux/thread_info.h>
#include <linux/sched.h>
#include <linux/gfp.h>
#include <linux/string.h>
#include <linux/elf.h>
#include <linux/mm.h>
#include <linux/module.h>

#include <asm/cpufeature.h>
#include <asm/msr.h>
#include <asm/pgtable.h>
#include <asm/unistd.h>

/*
 * Should the kernel map a VDSO page into processes and pass its
 * address down to glibc upon exec()?
 */
#ifdef CONFIG_PARAVIRT
unsigned int __read_mostly vdso_enabled = 0;
#else
unsigned int __read_mostly vdso_enabled = 1;
#endif

EXPORT_SYMBOL_GPL(vdso_enabled);

static int __init vdso_setup(char *s)
{
	vdso_enabled = simple_strtoul(s, NULL, 0);

	return 1;
}

__setup("vdso=", vdso_setup);

extern asmlinkage void sysenter_entry(void);

void enable_sep_cpu(void)
{
	int cpu = get_cpu();
	struct tss_struct *tss = &per_cpu(init_tss, cpu);

	if (!boot_cpu_has(X86_FEATURE_SEP)) {
		put_cpu();
		return;
	}

	tss->ss1 = __KERNEL_CS;
	tss->esp1 = sizeof(struct tss_struct) + (unsigned long) tss;
	wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0);
	wrmsr(MSR_IA32_SYSENTER_ESP, tss->esp1, 0);
	wrmsr(MSR_IA32_SYSENTER_EIP, (unsigned long) sysenter_entry, 0);
	put_cpu();	
}

/*
 * These symbols are defined by vsyscall.o to mark the bounds
 * of the ELF DSO images included therein.
 */
extern const char vsyscall_int80_start, vsyscall_int80_end;
extern const char vsyscall_sysenter_start, vsyscall_sysenter_end;
static struct page *syscall_pages[1];

int __cpuinit sysenter_setup(void)
{
	void *syscall_page = (void *)get_zeroed_page(GFP_ATOMIC);
	syscall_pages[0] = virt_to_page(syscall_page);

#ifdef CONFIG_COMPAT_VDSO
	__set_fixmap(FIX_VDSO, __pa(syscall_page), PAGE_READONLY_EXEC);
	printk("Compat vDSO mapped to %08lx.\n", __fix_to_virt(FIX_VDSO));
#endif

	if (!boot_cpu_has(X86_FEATURE_SEP)) {
		memcpy(syscall_page,
		       &vsyscall_int80_start,
		       &vsyscall_int80_end - &vsyscall_int80_start);
		return 0;
	}

	memcpy(syscall_page,
	       &vsyscall_sysenter_start,
	       &vsyscall_sysenter_end - &vsyscall_sysenter_start);

	return 0;
}

#ifndef CONFIG_COMPAT_VDSO
/* Defined in vsyscall-sysenter.S */
extern void SYSENTER_RETURN;

/* Setup a VMA at program startup for the vsyscall page */
int arch_setup_additional_pages(struct linux_binprm *bprm, int exstack)
{
	struct mm_struct *mm = current->mm;
	unsigned long addr;
	int ret;

	down_write(&mm->mmap_sem);
	addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
	if (IS_ERR_VALUE(addr)) {
		ret = addr;
		goto up_fail;
	}

	/*
	 * MAYWRITE to allow gdb to COW and set breakpoints
	 *
	 * Make sure the vDSO gets into every core dump.
	 * Dumping its contents makes post-mortem fully interpretable later
	 * without matching up the same kernel and hardware config to see
	 * what PC values meant.
	 */
	ret = install_special_mapping(mm, addr, PAGE_SIZE,
				      VM_READ|VM_EXEC|
				      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
				      VM_ALWAYSDUMP,
				      syscall_pages);
	if (ret)
		goto up_fail;

	current->mm->context.vdso = (void *)addr;
	current_thread_info()->sysenter_return =
				    (void *)VDSO_SYM(&SYSENTER_RETURN);
up_fail:
	up_write(&mm->mmap_sem);
	return ret;
}

const char *arch_vma_name(struct vm_area_struct *vma)
{
	if (vma->vm_mm && vma->vm_start == (long)vma->vm_mm->context.vdso)
		return "[vdso]";
	return NULL;
}

struct vm_area_struct *get_gate_vma(struct task_struct *tsk)
{
	return NULL;
}

int in_gate_area(struct task_struct *task, unsigned long addr)
{
	return 0;
}

int in_gate_area_no_task(unsigned long addr)
{
	return 0;
}
#endif