linux/arch/x86/entry/vsyscall/vsyscall_64.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2012-2014 Andy Lutomirski <[email protected]>
 *
 * Based on the original implementation which is:
 *  Copyright (C) 2001 Andrea Arcangeli <[email protected]> SuSE
 *  Copyright 2003 Andi Kleen, SuSE Labs.
 *
 *  Parts of the original code have been moved to arch/x86/vdso/vma.c
 *
 * This file implements vsyscall emulation.  vsyscalls are a legacy ABI:
 * Userspace can request certain kernel services by calling fixed
 * addresses.  This concept is problematic:
 *
 * - It interferes with ASLR.
 * - It's awkward to write code that lives in kernel addresses but is
 *   callable by userspace at fixed addresses.
 * - The whole concept is impossible for 32-bit compat userspace.
 * - UML cannot easily virtualize a vsyscall.
 *
 * As of mid-2014, I believe that there is no new userspace code that
 * will use a vsyscall if the vDSO is present.  I hope that there will
 * soon be no new userspace code that will ever use a vsyscall.
 *
 * The code in this file emulates vsyscalls when notified of a page
 * fault to a vsyscall address.
 */

#include <linux/kernel.h>
#include <linux/timer.h>
#include <linux/sched/signal.h>
#include <linux/mm_types.h>
#include <linux/syscalls.h>
#include <linux/ratelimit.h>

#include <asm/vsyscall.h>
#include <asm/unistd.h>
#include <asm/fixmap.h>
#include <asm/traps.h>
#include <asm/paravirt.h>

#define CREATE_TRACE_POINTS
#include "vsyscall_trace.h"

static enum { … } vsyscall_mode __ro_after_init = …NONE;
#elif defined(CONFIG_LEGACY_VSYSCALL_XONLY)
	XONLY;
#else
	#error VSYSCALL config is broken
#endif

static int __init vsyscall_setup(char *str)
{ … }
early_param(…);

static void warn_bad_vsyscall(const char *level, struct pt_regs *regs,
			      const char *message)
{ … }

static int addr_to_vsyscall_nr(unsigned long addr)
{ … }

static bool write_ok_or_segv(unsigned long ptr, size_t size)
{ … }

bool emulate_vsyscall(unsigned long error_code,
		      struct pt_regs *regs, unsigned long address)
{ … }

/*
 * A pseudo VMA to allow ptrace access for the vsyscall page.  This only
 * covers the 64bit vsyscall page now. 32bit has a real VMA now and does
 * not need special handling anymore:
 */
static const char *gate_vma_name(struct vm_area_struct *vma)
{ … }
static const struct vm_operations_struct gate_vma_ops = …;
static struct vm_area_struct gate_vma __ro_after_init = …;

struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
{ … }

int in_gate_area(struct mm_struct *mm, unsigned long addr)
{ … }

/*
 * Use this when you have no reliable mm, typically from interrupt
 * context. It is less reliable than using a task's mm and may give
 * false positives.
 */
int in_gate_area_no_mm(unsigned long addr)
{ … }

/*
 * The VSYSCALL page is the only user-accessible page in the kernel address
 * range.  Normally, the kernel page tables can have _PAGE_USER clear, but
 * the tables covering VSYSCALL_ADDR need _PAGE_USER set if vsyscalls
 * are enabled.
 *
 * Some day we may create a "minimal" vsyscall mode in which we emulate
 * vsyscalls but leave the page not present.  If so, we skip calling
 * this.
 */
void __init set_vsyscall_pgtable_user_bits(pgd_t *root)
{ … }

void __init map_vsyscall(void)
{ … }