355 lines
8.5 KiB
C
355 lines
8.5 KiB
C
/*
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* Copyright (C) 2001 Andrea Arcangeli <andrea@suse.de> SuSE
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* Copyright 2003 Andi Kleen, SuSE Labs.
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*
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* [ NOTE: this mechanism is now deprecated in favor of the vDSO. ]
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*
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* Thanks to hpa@transmeta.com for some useful hint.
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* Special thanks to Ingo Molnar for his early experience with
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* a different vsyscall implementation for Linux/IA32 and for the name.
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*
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* vsyscall 1 is located at -10Mbyte, vsyscall 2 is located
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* at virtual address -10Mbyte+1024bytes etc... There are at max 4
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* vsyscalls. One vsyscall can reserve more than 1 slot to avoid
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* jumping out of line if necessary. We cannot add more with this
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* mechanism because older kernels won't return -ENOSYS.
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*
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* Note: the concept clashes with user mode linux. UML users should
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* use the vDSO.
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/time.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/timer.h>
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#include <linux/seqlock.h>
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#include <linux/jiffies.h>
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#include <linux/sysctl.h>
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#include <linux/topology.h>
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#include <linux/timekeeper_internal.h>
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#include <linux/getcpu.h>
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#include <linux/cpu.h>
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#include <linux/smp.h>
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#include <linux/notifier.h>
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#include <linux/syscalls.h>
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#include <linux/ratelimit.h>
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#include <asm/vsyscall.h>
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#include <asm/pgtable.h>
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#include <asm/compat.h>
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#include <asm/page.h>
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#include <asm/unistd.h>
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#include <asm/fixmap.h>
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#include <asm/errno.h>
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#include <asm/io.h>
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#include <asm/segment.h>
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#include <asm/desc.h>
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#include <asm/topology.h>
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#include <asm/traps.h>
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#define CREATE_TRACE_POINTS
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#include "vsyscall_trace.h"
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DEFINE_VVAR(int, vgetcpu_mode);
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static enum { EMULATE, NATIVE, NONE } vsyscall_mode = EMULATE;
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static int __init vsyscall_setup(char *str)
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{
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if (str) {
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if (!strcmp("emulate", str))
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vsyscall_mode = EMULATE;
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else if (!strcmp("native", str))
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vsyscall_mode = NATIVE;
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else if (!strcmp("none", str))
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vsyscall_mode = NONE;
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else
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return -EINVAL;
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return 0;
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}
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return -EINVAL;
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}
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early_param("vsyscall", vsyscall_setup);
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static void warn_bad_vsyscall(const char *level, struct pt_regs *regs,
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const char *message)
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{
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if (!show_unhandled_signals)
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return;
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printk_ratelimited("%s%s[%d] %s ip:%lx cs:%lx sp:%lx ax:%lx si:%lx di:%lx\n",
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level, current->comm, task_pid_nr(current),
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message, regs->ip, regs->cs,
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regs->sp, regs->ax, regs->si, regs->di);
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}
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static int addr_to_vsyscall_nr(unsigned long addr)
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{
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int nr;
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if ((addr & ~0xC00UL) != VSYSCALL_ADDR)
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return -EINVAL;
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nr = (addr & 0xC00UL) >> 10;
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if (nr >= 3)
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return -EINVAL;
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return nr;
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}
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static bool write_ok_or_segv(unsigned long ptr, size_t size)
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{
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/*
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* XXX: if access_ok, get_user, and put_user handled
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* sig_on_uaccess_error, this could go away.
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*/
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if (!access_ok(VERIFY_WRITE, (void __user *)ptr, size)) {
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siginfo_t info;
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struct thread_struct *thread = ¤t->thread;
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thread->error_code = 6; /* user fault, no page, write */
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thread->cr2 = ptr;
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thread->trap_nr = X86_TRAP_PF;
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memset(&info, 0, sizeof(info));
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info.si_signo = SIGSEGV;
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info.si_errno = 0;
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info.si_code = SEGV_MAPERR;
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info.si_addr = (void __user *)ptr;
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force_sig_info(SIGSEGV, &info, current);
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return false;
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} else {
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return true;
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}
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}
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bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
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{
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struct task_struct *tsk;
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unsigned long caller;
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int vsyscall_nr, syscall_nr, tmp;
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int prev_sig_on_uaccess_error;
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long ret;
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/*
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* No point in checking CS -- the only way to get here is a user mode
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* trap to a high address, which means that we're in 64-bit user code.
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*/
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WARN_ON_ONCE(address != regs->ip);
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if (vsyscall_mode == NONE) {
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warn_bad_vsyscall(KERN_INFO, regs,
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"vsyscall attempted with vsyscall=none");
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return false;
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}
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vsyscall_nr = addr_to_vsyscall_nr(address);
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trace_emulate_vsyscall(vsyscall_nr);
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if (vsyscall_nr < 0) {
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warn_bad_vsyscall(KERN_WARNING, regs,
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"misaligned vsyscall (exploit attempt or buggy program) -- look up the vsyscall kernel parameter if you need a workaround");
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goto sigsegv;
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}
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if (get_user(caller, (unsigned long __user *)regs->sp) != 0) {
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warn_bad_vsyscall(KERN_WARNING, regs,
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"vsyscall with bad stack (exploit attempt?)");
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goto sigsegv;
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}
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tsk = current;
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/*
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* Check for access_ok violations and find the syscall nr.
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*
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* NULL is a valid user pointer (in the access_ok sense) on 32-bit and
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* 64-bit, so we don't need to special-case it here. For all the
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* vsyscalls, NULL means "don't write anything" not "write it at
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* address 0".
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*/
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switch (vsyscall_nr) {
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case 0:
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if (!write_ok_or_segv(regs->di, sizeof(struct timeval)) ||
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!write_ok_or_segv(regs->si, sizeof(struct timezone))) {
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ret = -EFAULT;
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goto check_fault;
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}
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syscall_nr = __NR_gettimeofday;
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break;
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case 1:
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if (!write_ok_or_segv(regs->di, sizeof(time_t))) {
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ret = -EFAULT;
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goto check_fault;
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}
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syscall_nr = __NR_time;
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break;
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case 2:
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if (!write_ok_or_segv(regs->di, sizeof(unsigned)) ||
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!write_ok_or_segv(regs->si, sizeof(unsigned))) {
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ret = -EFAULT;
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goto check_fault;
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}
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syscall_nr = __NR_getcpu;
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break;
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}
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/*
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* Handle seccomp. regs->ip must be the original value.
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* See seccomp_send_sigsys and Documentation/prctl/seccomp_filter.txt.
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*
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* We could optimize the seccomp disabled case, but performance
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* here doesn't matter.
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*/
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regs->orig_ax = syscall_nr;
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regs->ax = -ENOSYS;
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tmp = secure_computing(syscall_nr);
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if ((!tmp && regs->orig_ax != syscall_nr) || regs->ip != address) {
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warn_bad_vsyscall(KERN_DEBUG, regs,
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"seccomp tried to change syscall nr or ip");
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do_exit(SIGSYS);
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}
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if (tmp)
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goto do_ret; /* skip requested */
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/*
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* With a real vsyscall, page faults cause SIGSEGV. We want to
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* preserve that behavior to make writing exploits harder.
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*/
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prev_sig_on_uaccess_error = current_thread_info()->sig_on_uaccess_error;
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current_thread_info()->sig_on_uaccess_error = 1;
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ret = -EFAULT;
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switch (vsyscall_nr) {
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case 0:
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ret = sys_gettimeofday(
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(struct timeval __user *)regs->di,
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(struct timezone __user *)regs->si);
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break;
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case 1:
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ret = sys_time((time_t __user *)regs->di);
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break;
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case 2:
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ret = sys_getcpu((unsigned __user *)regs->di,
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(unsigned __user *)regs->si,
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NULL);
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break;
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}
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current_thread_info()->sig_on_uaccess_error = prev_sig_on_uaccess_error;
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check_fault:
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if (ret == -EFAULT) {
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/* Bad news -- userspace fed a bad pointer to a vsyscall. */
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warn_bad_vsyscall(KERN_INFO, regs,
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"vsyscall fault (exploit attempt?)");
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/*
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* If we failed to generate a signal for any reason,
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* generate one here. (This should be impossible.)
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*/
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if (WARN_ON_ONCE(!sigismember(&tsk->pending.signal, SIGBUS) &&
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!sigismember(&tsk->pending.signal, SIGSEGV)))
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goto sigsegv;
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return true; /* Don't emulate the ret. */
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}
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regs->ax = ret;
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do_ret:
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/* Emulate a ret instruction. */
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regs->ip = caller;
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regs->sp += 8;
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return true;
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sigsegv:
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force_sig(SIGSEGV, current);
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return true;
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}
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/*
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* Assume __initcall executes before all user space. Hopefully kmod
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* doesn't violate that. We'll find out if it does.
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*/
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static void vsyscall_set_cpu(int cpu)
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{
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unsigned long d;
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unsigned long node = 0;
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#ifdef CONFIG_NUMA
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node = cpu_to_node(cpu);
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#endif
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if (cpu_has(&cpu_data(cpu), X86_FEATURE_RDTSCP))
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write_rdtscp_aux((node << 12) | cpu);
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/*
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* Store cpu number in limit so that it can be loaded quickly
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* in user space in vgetcpu. (12 bits for the CPU and 8 bits for the node)
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*/
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d = 0x0f40000000000ULL;
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d |= cpu;
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d |= (node & 0xf) << 12;
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d |= (node >> 4) << 48;
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write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
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}
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static void cpu_vsyscall_init(void *arg)
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{
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/* preemption should be already off */
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vsyscall_set_cpu(raw_smp_processor_id());
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}
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static int
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cpu_vsyscall_notifier(struct notifier_block *n, unsigned long action, void *arg)
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{
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long cpu = (long)arg;
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if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN)
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smp_call_function_single(cpu, cpu_vsyscall_init, NULL, 1);
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return NOTIFY_DONE;
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}
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void __init map_vsyscall(void)
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{
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extern char __vsyscall_page;
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unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
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__set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall,
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vsyscall_mode == NATIVE
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? PAGE_KERNEL_VSYSCALL
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: PAGE_KERNEL_VVAR);
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BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=
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(unsigned long)VSYSCALL_ADDR);
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}
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static int __init vsyscall_init(void)
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{
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cpu_notifier_register_begin();
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on_each_cpu(cpu_vsyscall_init, NULL, 1);
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/* notifier priority > KVM */
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__hotcpu_notifier(cpu_vsyscall_notifier, 30);
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cpu_notifier_register_done();
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return 0;
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}
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__initcall(vsyscall_init);
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