/*
 *  Copyright (C) 2001 Andrea Arcangeli <andrea@suse.de> SuSE
 *  Copyright 2003 Andi Kleen, SuSE Labs.
 *
 *  [ NOTE: this mechanism is now deprecated in favor of the vDSO. ]
 *
 *  Thanks to hpa@transmeta.com for some useful hint.
 *  Special thanks to Ingo Molnar for his early experience with
 *  a different vsyscall implementation for Linux/IA32 and for the name.
 *
 *  vsyscall 1 is located at -10Mbyte, vsyscall 2 is located
 *  at virtual address -10Mbyte+1024bytes etc... There are at max 4
 *  vsyscalls. One vsyscall can reserve more than 1 slot to avoid
 *  jumping out of line if necessary. We cannot add more with this
 *  mechanism because older kernels won't return -ENOSYS.
 *
 *  Note: the concept clashes with user mode linux.  UML users should
 *  use the vDSO.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/time.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/timer.h>
#include <linux/seqlock.h>
#include <linux/jiffies.h>
#include <linux/sysctl.h>
#include <linux/topology.h>
#include <linux/timekeeper_internal.h>
#include <linux/getcpu.h>
#include <linux/cpu.h>
#include <linux/smp.h>
#include <linux/notifier.h>
#include <linux/syscalls.h>
#include <linux/ratelimit.h>

#include <asm/vsyscall.h>
#include <asm/pgtable.h>
#include <asm/compat.h>
#include <asm/page.h>
#include <asm/unistd.h>
#include <asm/fixmap.h>
#include <asm/errno.h>
#include <asm/io.h>
#include <asm/segment.h>
#include <asm/desc.h>
#include <asm/topology.h>
#include <asm/vgtod.h>
#include <asm/traps.h>

#define CREATE_TRACE_POINTS
#include "vsyscall_trace.h"

DEFINE_VVAR(int, vgetcpu_mode);
DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data);

static enum { EMULATE, NATIVE, NONE } vsyscall_mode = EMULATE;

static int __init vsyscall_setup(char *str)
{
        if (str) {
                if (!strcmp("emulate", str))
                        vsyscall_mode = EMULATE;
                else if (!strcmp("native", str))
                        vsyscall_mode = NATIVE;
                else if (!strcmp("none", str))
                        vsyscall_mode = NONE;
                else
                        return -EINVAL;

                return 0;
        }

        return -EINVAL;
}
early_param("vsyscall", vsyscall_setup);

void update_vsyscall_tz(void)
{
        vsyscall_gtod_data.sys_tz = sys_tz;
}

void update_vsyscall(struct timekeeper *tk)
{
        struct vsyscall_gtod_data *vdata = &vsyscall_gtod_data;

        write_seqcount_begin(&vdata->seq);

        /* copy vsyscall data */
        vdata->clock.vclock_mode        = tk->clock->archdata.vclock_mode;
        vdata->clock.cycle_last         = tk->clock->cycle_last;
        vdata->clock.mask               = tk->clock->mask;
        vdata->clock.mult               = tk->mult;
        vdata->clock.shift              = tk->shift;

        vdata->wall_time_sec            = tk->xtime_sec;
        vdata->wall_time_snsec          = tk->xtime_nsec;

        vdata->monotonic_time_sec       = tk->xtime_sec
                                        + tk->wall_to_monotonic.tv_sec;
        vdata->monotonic_time_snsec     = tk->xtime_nsec
                                        + (tk->wall_to_monotonic.tv_nsec
                                                << tk->shift);
        while (vdata->monotonic_time_snsec >=
                                        (((u64)NSEC_PER_SEC) << tk->shift)) {
                vdata->monotonic_time_snsec -=
                                        ((u64)NSEC_PER_SEC) << tk->shift;
                vdata->monotonic_time_sec++;
        }

        vdata->wall_time_coarse.tv_sec  = tk->xtime_sec;
        vdata->wall_time_coarse.tv_nsec = (long)(tk->xtime_nsec >> tk->shift);

        vdata->monotonic_time_coarse    = timespec_add(vdata->wall_time_coarse,
                                                        tk->wall_to_monotonic);

        write_seqcount_end(&vdata->seq);
}

static void warn_bad_vsyscall(const char *level, struct pt_regs *regs,
                              const char *message)
{
        if (!show_unhandled_signals)
                return;

        pr_notice_ratelimited("%s%s[%d] %s ip:%lx cs:%lx sp:%lx ax:%lx si:%lx di:%lx\n",
                              level, current->comm, task_pid_nr(current),
                              message, regs->ip, regs->cs,
                              regs->sp, regs->ax, regs->si, regs->di);
}

static int addr_to_vsyscall_nr(unsigned long addr)
{
        int nr;

        if ((addr & ~0xC00UL) != VSYSCALL_START)
                return -EINVAL;

        nr = (addr & 0xC00UL) >> 10;
        if (nr >= 3)
                return -EINVAL;

        return nr;
}

static bool write_ok_or_segv(unsigned long ptr, size_t size)
{
        /*
         * XXX: if access_ok, get_user, and put_user handled
         * sig_on_uaccess_error, this could go away.
         */

        if (!access_ok(VERIFY_WRITE, (void __user *)ptr, size)) {
                siginfo_t info;
                struct thread_struct *thread = &current->thread;

                thread->error_code      = 6;  /* user fault, no page, write */
                thread->cr2             = ptr;
                thread->trap_nr         = X86_TRAP_PF;

                memset(&info, 0, sizeof(info));
                info.si_signo           = SIGSEGV;
                info.si_errno           = 0;
                info.si_code            = SEGV_MAPERR;
                info.si_addr            = (void __user *)ptr;

                force_sig_info(SIGSEGV, &info, current);
                return false;
        } else {
                return true;
        }
}

bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
{
        struct task_struct *tsk;
        unsigned long caller;
        int vsyscall_nr, syscall_nr, tmp;
        int prev_sig_on_uaccess_error;
        long ret;

        /*
         * No point in checking CS -- the only way to get here is a user mode
         * trap to a high address, which means that we're in 64-bit user code.
         */

        WARN_ON_ONCE(address != regs->ip);

        if (vsyscall_mode == NONE) {
                warn_bad_vsyscall(KERN_INFO, regs,
                                  "vsyscall attempted with vsyscall=none");
                return false;
        }

        vsyscall_nr = addr_to_vsyscall_nr(address);

        trace_emulate_vsyscall(vsyscall_nr);

        if (vsyscall_nr < 0) {
                warn_bad_vsyscall(KERN_WARNING, regs,
                                  "misaligned vsyscall (exploit attempt or buggy program) -- look up the vsyscall kernel parameter if you need a workaround");
                goto sigsegv;
        }

        if (get_user(caller, (unsigned long __user *)regs->sp) != 0) {
                warn_bad_vsyscall(KERN_WARNING, regs,
                                  "vsyscall with bad stack (exploit attempt?)");
                goto sigsegv;
        }

        tsk = current;

        /*
         * Check for access_ok violations and find the syscall nr.
         *
         * NULL is a valid user pointer (in the access_ok sense) on 32-bit and
         * 64-bit, so we don't need to special-case it here.  For all the
         * vsyscalls, NULL means "don't write anything" not "write it at
         * address 0".
         */
        switch (vsyscall_nr) {
        case 0:
                if (!write_ok_or_segv(regs->di, sizeof(struct timeval)) ||
                    !write_ok_or_segv(regs->si, sizeof(struct timezone))) {
                        ret = -EFAULT;
                        goto check_fault;
                }

                syscall_nr = __NR_gettimeofday;
                break;

        case 1:
                if (!write_ok_or_segv(regs->di, sizeof(time_t))) {
                        ret = -EFAULT;
                        goto check_fault;
                }

                syscall_nr = __NR_time;
                break;

        case 2:
                if (!write_ok_or_segv(regs->di, sizeof(unsigned)) ||
                    !write_ok_or_segv(regs->si, sizeof(unsigned))) {
                        ret = -EFAULT;
                        goto check_fault;
                }

                syscall_nr = __NR_getcpu;
                break;
        }

        /*
         * Handle seccomp.  regs->ip must be the original value.
         * See seccomp_send_sigsys and Documentation/prctl/seccomp_filter.txt.
         *
         * We could optimize the seccomp disabled case, but performance
         * here doesn't matter.
         */
        regs->orig_ax = syscall_nr;
        regs->ax = -ENOSYS;
        tmp = secure_computing(syscall_nr);
        if ((!tmp && regs->orig_ax != syscall_nr) || regs->ip != address) {
                warn_bad_vsyscall(KERN_DEBUG, regs,
                                  "seccomp tried to change syscall nr or ip");
                do_exit(SIGSYS);
        }
        if (tmp)
                goto do_ret;  /* skip requested */

        /*
         * With a real vsyscall, page faults cause SIGSEGV.  We want to
         * preserve that behavior to make writing exploits harder.
         */
        prev_sig_on_uaccess_error = current_thread_info()->sig_on_uaccess_error;
        current_thread_info()->sig_on_uaccess_error = 1;

        ret = -EFAULT;
        switch (vsyscall_nr) {
        case 0:
                ret = sys_gettimeofday(
                        (struct timeval __user *)regs->di,
                        (struct timezone __user *)regs->si);
                break;

        case 1:
                ret = sys_time((time_t __user *)regs->di);
                break;

        case 2:
                ret = sys_getcpu((unsigned __user *)regs->di,
                                 (unsigned __user *)regs->si,
                                 NULL);
                break;
        }

        current_thread_info()->sig_on_uaccess_error = prev_sig_on_uaccess_error;

check_fault:
        if (ret == -EFAULT) {
                /* Bad news -- userspace fed a bad pointer to a vsyscall. */
                warn_bad_vsyscall(KERN_INFO, regs,
                                  "vsyscall fault (exploit attempt?)");

                /*
                 * If we failed to generate a signal for any reason,
                 * generate one here.  (This should be impossible.)
                 */
                if (WARN_ON_ONCE(!sigismember(&tsk->pending.signal, SIGBUS) &&
                                 !sigismember(&tsk->pending.signal, SIGSEGV)))
                        goto sigsegv;

                return true;  /* Don't emulate the ret. */
        }

        regs->ax = ret;

do_ret:
        /* Emulate a ret instruction. */
        regs->ip = caller;
        regs->sp += 8;
        return true;

sigsegv:
        force_sig(SIGSEGV, current);
        return true;
}

/*
 * Assume __initcall executes before all user space. Hopefully kmod
 * doesn't violate that. We'll find out if it does.
 */
static void vsyscall_set_cpu(int cpu)
{
        unsigned long d;
        unsigned long node = 0;
#ifdef CONFIG_NUMA
        node = cpu_to_node(cpu);
#endif
        if (cpu_has(&cpu_data(cpu), X86_FEATURE_RDTSCP))
                write_rdtscp_aux((node << 12) | cpu);

        /*
         * Store cpu number in limit so that it can be loaded quickly
         * in user space in vgetcpu. (12 bits for the CPU and 8 bits for the node)
         */
        d = 0x0f40000000000ULL;
        d |= cpu;
        d |= (node & 0xf) << 12;
        d |= (node >> 4) << 48;

        write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
}

static void cpu_vsyscall_init(void *arg)
{
        /* preemption should be already off */
        vsyscall_set_cpu(raw_smp_processor_id());
}

static int
cpu_vsyscall_notifier(struct notifier_block *n, unsigned long action, void *arg)
{
        long cpu = (long)arg;

        if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN)
                smp_call_function_single(cpu, cpu_vsyscall_init, NULL, 1);

        return NOTIFY_DONE;
}

void __init map_vsyscall(void)
{
        extern char __vsyscall_page;
        unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
        extern char __vvar_page;
        unsigned long physaddr_vvar_page = __pa_symbol(&__vvar_page);

        __set_fixmap(VSYSCALL_FIRST_PAGE, physaddr_vsyscall,
                     vsyscall_mode == NATIVE
                     ? PAGE_KERNEL_VSYSCALL
                     : PAGE_KERNEL_VVAR);
        BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_FIRST_PAGE) !=
                     (unsigned long)VSYSCALL_START);

        __set_fixmap(VVAR_PAGE, physaddr_vvar_page, PAGE_KERNEL_VVAR);
        BUILD_BUG_ON((unsigned long)__fix_to_virt(VVAR_PAGE) !=
                     (unsigned long)VVAR_ADDRESS);
}

static int __init vsyscall_init(void)
{
        BUG_ON(VSYSCALL_ADDR(0) != __fix_to_virt(VSYSCALL_FIRST_PAGE));

        on_each_cpu(cpu_vsyscall_init, NULL, 1);
        /* notifier priority > KVM */
        hotcpu_notifier(cpu_vsyscall_notifier, 30);

        return 0;
}
__initcall(vsyscall_init);