1 files changed, 375 insertions, 0 deletions
diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
new file mode 100644
index 000000000..82ed001e8
--- /dev/null
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -0,0 +1,375 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2012-2014 Andy Lutomirski <luto@amacapital.net>
+ *
+ * Based on the original implementation which is:
+ *  Copyright (C) 2001 Andrea Arcangeli <andrea@suse.de> 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 { EMULATE, NONE } vsyscall_mode =
+#ifdef CONFIG_LEGACY_VSYSCALL_NONE
+	NONE;
+#else
+	EMULATE;
+#endif
+
+static int __init vsyscall_setup(char *str)
+{
+	if (str) {
+		if (!strcmp("emulate", str))
+			vsyscall_mode = EMULATE;
+		else if (!strcmp("none", str))
+			vsyscall_mode = NONE;
+		else
+			return -EINVAL;
+
+		return 0;
+	}
+
+	return -EINVAL;
+}
+early_param("vsyscall", vsyscall_setup);
+
+static void warn_bad_vsyscall(const char *level, struct pt_regs *regs,
+			      const char *message)
+{
+	if (!show_unhandled_signals)
+		return;
+
+	printk_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_ADDR)
+		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_err, 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;
+
+		clear_siginfo(&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_err;
+	long ret;
+	unsigned long orig_dx;
+
+	/*
+	 * 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/userspace-api/seccomp_filter.rst.
+	 *
+	 * We could optimize the seccomp disabled case, but performance
+	 * here doesn't matter.
+	 */
+	regs->orig_ax = syscall_nr;
+	regs->ax = -ENOSYS;
+	tmp = secure_computing(NULL);
+	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);
+	}
+	regs->orig_ax = -1;
+	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_err = current->thread.sig_on_uaccess_err;
+	current->thread.sig_on_uaccess_err = 1;
+
+	ret = -EFAULT;
+	switch (vsyscall_nr) {
+	case 0:
+		/* this decodes regs->di and regs->si on its own */
+		ret = __x64_sys_gettimeofday(regs);
+		break;
+
+	case 1:
+		/* this decodes regs->di on its own */
+		ret = __x64_sys_time(regs);
+		break;
+
+	case 2:
+		/* while we could clobber regs->dx, we didn't in the past... */
+		orig_dx = regs->dx;
+		regs->dx = 0;
+		/* this decodes regs->di, regs->si and regs->dx on its own */
+		ret = __x64_sys_getcpu(regs);
+		regs->dx = orig_dx;
+		break;
+	}
+
+	current->thread.sig_on_uaccess_err = prev_sig_on_uaccess_err;
+
+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;
+}
+
+/*
+ * 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)
+{
+	return "[vsyscall]";
+}
+static const struct vm_operations_struct gate_vma_ops = {
+	.name = gate_vma_name,
+};
+static struct vm_area_struct gate_vma = {
+	.vm_start	= VSYSCALL_ADDR,
+	.vm_end		= VSYSCALL_ADDR + PAGE_SIZE,
+	.vm_page_prot	= PAGE_READONLY_EXEC,
+	.vm_flags	= VM_READ | VM_EXEC,
+	.vm_ops		= &gate_vma_ops,
+};
+
+struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
+{
+#ifdef CONFIG_COMPAT
+	if (!mm || mm->context.ia32_compat)
+		return NULL;
+#endif
+	if (vsyscall_mode == NONE)
+		return NULL;
+	return &gate_vma;
+}
+
+int in_gate_area(struct mm_struct *mm, unsigned long addr)
+{
+	struct vm_area_struct *vma = get_gate_vma(mm);
+
+	if (!vma)
+		return 0;
+
+	return (addr >= vma->vm_start) && (addr < vma->vm_end);
+}
+
+/*
+ * 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)
+{
+	return vsyscall_mode != NONE && (addr & PAGE_MASK) == VSYSCALL_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)
+{
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+
+	pgd = pgd_offset_pgd(root, VSYSCALL_ADDR);
+	set_pgd(pgd, __pgd(pgd_val(*pgd) | _PAGE_USER));
+	p4d = p4d_offset(pgd, VSYSCALL_ADDR);
+#if CONFIG_PGTABLE_LEVELS >= 5
+	set_p4d(p4d, __p4d(p4d_val(*p4d) | _PAGE_USER));
+#endif
+	pud = pud_offset(p4d, VSYSCALL_ADDR);
+	set_pud(pud, __pud(pud_val(*pud) | _PAGE_USER));
+	pmd = pmd_offset(pud, VSYSCALL_ADDR);
+	set_pmd(pmd, __pmd(pmd_val(*pmd) | _PAGE_USER));
+}
+
+void __init map_vsyscall(void)
+{
+	extern char __vsyscall_page;
+	unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
+
+	if (vsyscall_mode != NONE) {
+		__set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall,
+			     PAGE_KERNEL_VVAR);
+		set_vsyscall_pgtable_user_bits(swapper_pg_dir);
+	}
+
+	BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=
+		     (unsigned long)VSYSCALL_ADDR);
+}