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>
40 #include <asm/paravirt.h>
42 #define CREATE_TRACE_POINTS
43 #include "vsyscall_trace.h"
45 static enum { EMULATE, NATIVE, NONE } vsyscall_mode =
46 #if defined(CONFIG_LEGACY_VSYSCALL_NATIVE)
48 #elif defined(CONFIG_LEGACY_VSYSCALL_NONE)
54 static int __init vsyscall_setup(char *str)
57 if (!strcmp("emulate", str))
58 vsyscall_mode = EMULATE;
59 else if (!strcmp("native", str))
60 vsyscall_mode = NATIVE;
61 else if (!strcmp("none", str))
71 early_param("vsyscall", vsyscall_setup);
73 static void warn_bad_vsyscall(const char *level, struct pt_regs *regs,
76 if (!show_unhandled_signals)
79 printk_ratelimited("%s%s[%d] %s ip:%lx cs:%lx sp:%lx ax:%lx si:%lx di:%lx\n",
80 level, current->comm, task_pid_nr(current),
81 message, regs->ip, regs->cs,
82 regs->sp, regs->ax, regs->si, regs->di);
85 static int addr_to_vsyscall_nr(unsigned long addr)
89 if ((addr & ~0xC00UL) != VSYSCALL_ADDR)
92 nr = (addr & 0xC00UL) >> 10;
99 static bool write_ok_or_segv(unsigned long ptr, size_t size)
102 * XXX: if access_ok, get_user, and put_user handled
103 * sig_on_uaccess_err, this could go away.
106 if (!access_ok(VERIFY_WRITE, (void __user *)ptr, size)) {
108 struct thread_struct *thread = ¤t->thread;
110 thread->error_code = 6; /* user fault, no page, write */
112 thread->trap_nr = X86_TRAP_PF;
114 memset(&info, 0, sizeof(info));
115 info.si_signo = SIGSEGV;
117 info.si_code = SEGV_MAPERR;
118 info.si_addr = (void __user *)ptr;
120 force_sig_info(SIGSEGV, &info, current);
127 bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
129 struct task_struct *tsk;
130 unsigned long caller;
131 int vsyscall_nr, syscall_nr, tmp;
132 int prev_sig_on_uaccess_err;
136 * No point in checking CS -- the only way to get here is a user mode
137 * trap to a high address, which means that we're in 64-bit user code.
140 WARN_ON_ONCE(address != regs->ip);
142 /* This should be unreachable in NATIVE mode. */
143 if (WARN_ON(vsyscall_mode == NATIVE))
146 if (vsyscall_mode == NONE) {
147 warn_bad_vsyscall(KERN_INFO, regs,
148 "vsyscall attempted with vsyscall=none");
152 vsyscall_nr = addr_to_vsyscall_nr(address);
154 trace_emulate_vsyscall(vsyscall_nr);
156 if (vsyscall_nr < 0) {
157 warn_bad_vsyscall(KERN_WARNING, regs,
158 "misaligned vsyscall (exploit attempt or buggy program) -- look up the vsyscall kernel parameter if you need a workaround");
162 if (get_user(caller, (unsigned long __user *)regs->sp) != 0) {
163 warn_bad_vsyscall(KERN_WARNING, regs,
164 "vsyscall with bad stack (exploit attempt?)");
171 * Check for access_ok violations and find the syscall nr.
173 * NULL is a valid user pointer (in the access_ok sense) on 32-bit and
174 * 64-bit, so we don't need to special-case it here. For all the
175 * vsyscalls, NULL means "don't write anything" not "write it at
178 switch (vsyscall_nr) {
180 if (!write_ok_or_segv(regs->di, sizeof(struct timeval)) ||
181 !write_ok_or_segv(regs->si, sizeof(struct timezone))) {
186 syscall_nr = __NR_gettimeofday;
190 if (!write_ok_or_segv(regs->di, sizeof(time_t))) {
195 syscall_nr = __NR_time;
199 if (!write_ok_or_segv(regs->di, sizeof(unsigned)) ||
200 !write_ok_or_segv(regs->si, sizeof(unsigned))) {
205 syscall_nr = __NR_getcpu;
210 * Handle seccomp. regs->ip must be the original value.
211 * See seccomp_send_sigsys and Documentation/prctl/seccomp_filter.txt.
213 * We could optimize the seccomp disabled case, but performance
214 * here doesn't matter.
216 regs->orig_ax = syscall_nr;
218 tmp = secure_computing(NULL);
219 if ((!tmp && regs->orig_ax != syscall_nr) || regs->ip != address) {
220 warn_bad_vsyscall(KERN_DEBUG, regs,
221 "seccomp tried to change syscall nr or ip");
226 goto do_ret; /* skip requested */
229 * With a real vsyscall, page faults cause SIGSEGV. We want to
230 * preserve that behavior to make writing exploits harder.
232 prev_sig_on_uaccess_err = current->thread.sig_on_uaccess_err;
233 current->thread.sig_on_uaccess_err = 1;
236 switch (vsyscall_nr) {
238 ret = sys_gettimeofday(
239 (struct timeval __user *)regs->di,
240 (struct timezone __user *)regs->si);
244 ret = sys_time((time_t __user *)regs->di);
248 ret = sys_getcpu((unsigned __user *)regs->di,
249 (unsigned __user *)regs->si,
254 current->thread.sig_on_uaccess_err = prev_sig_on_uaccess_err;
257 if (ret == -EFAULT) {
258 /* Bad news -- userspace fed a bad pointer to a vsyscall. */
259 warn_bad_vsyscall(KERN_INFO, regs,
260 "vsyscall fault (exploit attempt?)");
263 * If we failed to generate a signal for any reason,
264 * generate one here. (This should be impossible.)
266 if (WARN_ON_ONCE(!sigismember(&tsk->pending.signal, SIGBUS) &&
267 !sigismember(&tsk->pending.signal, SIGSEGV)))
270 return true; /* Don't emulate the ret. */
276 /* Emulate a ret instruction. */
282 force_sig(SIGSEGV, current);
287 * A pseudo VMA to allow ptrace access for the vsyscall page. This only
288 * covers the 64bit vsyscall page now. 32bit has a real VMA now and does
289 * not need special handling anymore:
291 static const char *gate_vma_name(struct vm_area_struct *vma)
295 static const struct vm_operations_struct gate_vma_ops = {
296 .name = gate_vma_name,
298 static struct vm_area_struct gate_vma = {
299 .vm_start = VSYSCALL_ADDR,
300 .vm_end = VSYSCALL_ADDR + PAGE_SIZE,
301 .vm_page_prot = PAGE_READONLY_EXEC,
302 .vm_flags = VM_READ | VM_EXEC,
303 .vm_ops = &gate_vma_ops,
306 struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
309 if (!mm || mm->context.ia32_compat)
312 if (vsyscall_mode == NONE)
317 int in_gate_area(struct mm_struct *mm, unsigned long addr)
319 struct vm_area_struct *vma = get_gate_vma(mm);
324 return (addr >= vma->vm_start) && (addr < vma->vm_end);
328 * Use this when you have no reliable mm, typically from interrupt
329 * context. It is less reliable than using a task's mm and may give
332 int in_gate_area_no_mm(unsigned long addr)
334 return vsyscall_mode != NONE && (addr & PAGE_MASK) == VSYSCALL_ADDR;
338 * The VSYSCALL page is the only user-accessible page in the kernel address
339 * range. Normally, the kernel page tables can have _PAGE_USER clear, but
340 * the tables covering VSYSCALL_ADDR need _PAGE_USER set if vsyscalls
343 * Some day we may create a "minimal" vsyscall mode in which we emulate
344 * vsyscalls but leave the page not present. If so, we skip calling
347 void __init set_vsyscall_pgtable_user_bits(pgd_t *root)
354 pgd = pgd_offset_pgd(root, VSYSCALL_ADDR);
355 set_pgd(pgd, __pgd(pgd_val(*pgd) | _PAGE_USER));
356 p4d = p4d_offset(pgd, VSYSCALL_ADDR);
357 #if CONFIG_PGTABLE_LEVELS >= 5
358 set_p4d(p4d, __p4d(p4d_val(*p4d) | _PAGE_USER));
360 pud = pud_offset(p4d, VSYSCALL_ADDR);
361 set_pud(pud, __pud(pud_val(*pud) | _PAGE_USER));
362 pmd = pmd_offset(pud, VSYSCALL_ADDR);
363 set_pmd(pmd, __pmd(pmd_val(*pmd) | _PAGE_USER));
366 void __init map_vsyscall(void)
368 extern char __vsyscall_page;
369 unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
371 if (vsyscall_mode != NONE) {
372 __set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall,
373 vsyscall_mode == NATIVE
374 ? PAGE_KERNEL_VSYSCALL
376 set_vsyscall_pgtable_user_bits(swapper_pg_dir);
379 BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=
380 (unsigned long)VSYSCALL_ADDR);