1 // SPDX-License-Identifier: GPL-2.0
3 * Copyright (c) 2012-2014 Andy Lutomirski <luto@amacapital.net>
5 * Based on the original implementation which is:
6 * Copyright (C) 2001 Andrea Arcangeli <andrea@suse.de> SuSE
7 * Copyright 2003 Andi Kleen, SuSE Labs.
9 * Parts of the original code have been moved to arch/x86/vdso/vma.c
11 * This file implements vsyscall emulation. vsyscalls are a legacy ABI:
12 * Userspace can request certain kernel services by calling fixed
13 * addresses. This concept is problematic:
15 * - It interferes with ASLR.
16 * - It's awkward to write code that lives in kernel addresses but is
17 * callable by userspace at fixed addresses.
18 * - The whole concept is impossible for 32-bit compat userspace.
19 * - UML cannot easily virtualize a vsyscall.
21 * As of mid-2014, I believe that there is no new userspace code that
22 * will use a vsyscall if the vDSO is present. I hope that there will
23 * soon be no new userspace code that will ever use a vsyscall.
25 * The code in this file emulates vsyscalls when notified of a page
26 * fault to a vsyscall address.
29 #include <linux/kernel.h>
30 #include <linux/timer.h>
31 #include <linux/sched/signal.h>
32 #include <linux/mm_types.h>
33 #include <linux/syscalls.h>
34 #include <linux/ratelimit.h>
36 #include <asm/vsyscall.h>
37 #include <asm/unistd.h>
38 #include <asm/fixmap.h>
39 #include <asm/traps.h>
41 #define CREATE_TRACE_POINTS
42 #include "vsyscall_trace.h"
44 static enum { EMULATE, NATIVE, NONE } vsyscall_mode =
45 #if defined(CONFIG_LEGACY_VSYSCALL_NATIVE)
47 #elif defined(CONFIG_LEGACY_VSYSCALL_NONE)
53 static int __init vsyscall_setup(char *str)
56 if (!strcmp("emulate", str))
57 vsyscall_mode = EMULATE;
58 else if (!strcmp("native", str))
59 vsyscall_mode = NATIVE;
60 else if (!strcmp("none", str))
70 early_param("vsyscall", vsyscall_setup);
72 static void warn_bad_vsyscall(const char *level, struct pt_regs *regs,
75 if (!show_unhandled_signals)
78 printk_ratelimited("%s%s[%d] %s ip:%lx cs:%lx sp:%lx ax:%lx si:%lx di:%lx\n",
79 level, current->comm, task_pid_nr(current),
80 message, regs->ip, regs->cs,
81 regs->sp, regs->ax, regs->si, regs->di);
84 static int addr_to_vsyscall_nr(unsigned long addr)
88 if ((addr & ~0xC00UL) != VSYSCALL_ADDR)
91 nr = (addr & 0xC00UL) >> 10;
98 static bool write_ok_or_segv(unsigned long ptr, size_t size)
101 * XXX: if access_ok, get_user, and put_user handled
102 * sig_on_uaccess_err, this could go away.
105 if (!access_ok(VERIFY_WRITE, (void __user *)ptr, size)) {
107 struct thread_struct *thread = ¤t->thread;
109 thread->error_code = 6; /* user fault, no page, write */
111 thread->trap_nr = X86_TRAP_PF;
113 memset(&info, 0, sizeof(info));
114 info.si_signo = SIGSEGV;
116 info.si_code = SEGV_MAPERR;
117 info.si_addr = (void __user *)ptr;
119 force_sig_info(SIGSEGV, &info, current);
126 bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
128 struct task_struct *tsk;
129 unsigned long caller;
130 int vsyscall_nr, syscall_nr, tmp;
131 int prev_sig_on_uaccess_err;
135 * No point in checking CS -- the only way to get here is a user mode
136 * trap to a high address, which means that we're in 64-bit user code.
139 WARN_ON_ONCE(address != regs->ip);
141 if (vsyscall_mode == NONE) {
142 warn_bad_vsyscall(KERN_INFO, regs,
143 "vsyscall attempted with vsyscall=none");
147 vsyscall_nr = addr_to_vsyscall_nr(address);
149 trace_emulate_vsyscall(vsyscall_nr);
151 if (vsyscall_nr < 0) {
152 warn_bad_vsyscall(KERN_WARNING, regs,
153 "misaligned vsyscall (exploit attempt or buggy program) -- look up the vsyscall kernel parameter if you need a workaround");
157 if (get_user(caller, (unsigned long __user *)regs->sp) != 0) {
158 warn_bad_vsyscall(KERN_WARNING, regs,
159 "vsyscall with bad stack (exploit attempt?)");
166 * Check for access_ok violations and find the syscall nr.
168 * NULL is a valid user pointer (in the access_ok sense) on 32-bit and
169 * 64-bit, so we don't need to special-case it here. For all the
170 * vsyscalls, NULL means "don't write anything" not "write it at
173 switch (vsyscall_nr) {
175 if (!write_ok_or_segv(regs->di, sizeof(struct timeval)) ||
176 !write_ok_or_segv(regs->si, sizeof(struct timezone))) {
181 syscall_nr = __NR_gettimeofday;
185 if (!write_ok_or_segv(regs->di, sizeof(time_t))) {
190 syscall_nr = __NR_time;
194 if (!write_ok_or_segv(regs->di, sizeof(unsigned)) ||
195 !write_ok_or_segv(regs->si, sizeof(unsigned))) {
200 syscall_nr = __NR_getcpu;
205 * Handle seccomp. regs->ip must be the original value.
206 * See seccomp_send_sigsys and Documentation/prctl/seccomp_filter.txt.
208 * We could optimize the seccomp disabled case, but performance
209 * here doesn't matter.
211 regs->orig_ax = syscall_nr;
213 tmp = secure_computing(NULL);
214 if ((!tmp && regs->orig_ax != syscall_nr) || regs->ip != address) {
215 warn_bad_vsyscall(KERN_DEBUG, regs,
216 "seccomp tried to change syscall nr or ip");
221 goto do_ret; /* skip requested */
224 * With a real vsyscall, page faults cause SIGSEGV. We want to
225 * preserve that behavior to make writing exploits harder.
227 prev_sig_on_uaccess_err = current->thread.sig_on_uaccess_err;
228 current->thread.sig_on_uaccess_err = 1;
231 switch (vsyscall_nr) {
233 ret = sys_gettimeofday(
234 (struct timeval __user *)regs->di,
235 (struct timezone __user *)regs->si);
239 ret = sys_time((time_t __user *)regs->di);
243 ret = sys_getcpu((unsigned __user *)regs->di,
244 (unsigned __user *)regs->si,
249 current->thread.sig_on_uaccess_err = prev_sig_on_uaccess_err;
252 if (ret == -EFAULT) {
253 /* Bad news -- userspace fed a bad pointer to a vsyscall. */
254 warn_bad_vsyscall(KERN_INFO, regs,
255 "vsyscall fault (exploit attempt?)");
258 * If we failed to generate a signal for any reason,
259 * generate one here. (This should be impossible.)
261 if (WARN_ON_ONCE(!sigismember(&tsk->pending.signal, SIGBUS) &&
262 !sigismember(&tsk->pending.signal, SIGSEGV)))
265 return true; /* Don't emulate the ret. */
271 /* Emulate a ret instruction. */
277 force_sig(SIGSEGV, current);
282 * A pseudo VMA to allow ptrace access for the vsyscall page. This only
283 * covers the 64bit vsyscall page now. 32bit has a real VMA now and does
284 * not need special handling anymore:
286 static const char *gate_vma_name(struct vm_area_struct *vma)
290 static const struct vm_operations_struct gate_vma_ops = {
291 .name = gate_vma_name,
293 static struct vm_area_struct gate_vma = {
294 .vm_start = VSYSCALL_ADDR,
295 .vm_end = VSYSCALL_ADDR + PAGE_SIZE,
296 .vm_page_prot = PAGE_READONLY_EXEC,
297 .vm_flags = VM_READ | VM_EXEC,
298 .vm_ops = &gate_vma_ops,
301 struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
304 if (!mm || mm->context.ia32_compat)
307 if (vsyscall_mode == NONE)
312 int in_gate_area(struct mm_struct *mm, unsigned long addr)
314 struct vm_area_struct *vma = get_gate_vma(mm);
319 return (addr >= vma->vm_start) && (addr < vma->vm_end);
323 * Use this when you have no reliable mm, typically from interrupt
324 * context. It is less reliable than using a task's mm and may give
327 int in_gate_area_no_mm(unsigned long addr)
329 return vsyscall_mode != NONE && (addr & PAGE_MASK) == VSYSCALL_ADDR;
332 void __init map_vsyscall(void)
334 extern char __vsyscall_page;
335 unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
337 if (vsyscall_mode != NONE)
338 __set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall,
339 vsyscall_mode == NATIVE
340 ? PAGE_KERNEL_VSYSCALL
343 BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=
344 (unsigned long)VSYSCALL_ADDR);