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@@ -1,59 +1,43 @@
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/*
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+ * Copyright (c) 2012-2014 Andy Lutomirski <luto@amacapital.net>
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+ *
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+ * Based on the original implementation which is:
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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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+ * Parts of the original code have been moved to arch/x86/vdso/vma.c
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+ *
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+ * This file implements vsyscall emulation. vsyscalls are a legacy ABI:
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+ * Userspace can request certain kernel services by calling fixed
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+ * addresses. This concept is problematic:
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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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+ * - It interferes with ASLR.
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+ * - It's awkward to write code that lives in kernel addresses but is
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+ * callable by userspace at fixed addresses.
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+ * - The whole concept is impossible for 32-bit compat userspace.
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+ * - UML cannot easily virtualize a vsyscall.
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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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+ * As of mid-2014, I believe that there is no new userspace code that
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+ * will use a vsyscall if the vDSO is present. I hope that there will
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+ * soon be no new userspace code that will ever use a vsyscall.
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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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+ * The code in this file emulates vsyscalls when notified of a page
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+ * fault to a vsyscall address.
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*/
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-#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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-
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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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-
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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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@@ -222,6 +206,7 @@ bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)
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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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+ regs->orig_ax = -1;
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if (tmp)
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goto do_ret; /* skip requested */
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@@ -284,46 +269,54 @@ sigsegv:
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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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+ * A pseudo VMA to allow ptrace access for the vsyscall page. This only
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+ * covers the 64bit vsyscall page now. 32bit has a real VMA now and does
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+ * not need special handling anymore:
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*/
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-static void vsyscall_set_cpu(int cpu)
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+static const char *gate_vma_name(struct vm_area_struct *vma)
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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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- /*
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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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-
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- write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
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+ return "[vsyscall]";
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}
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-
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-static void cpu_vsyscall_init(void *arg)
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+static struct vm_operations_struct gate_vma_ops = {
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+ .name = gate_vma_name,
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+};
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+static struct vm_area_struct gate_vma = {
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+ .vm_start = VSYSCALL_ADDR,
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+ .vm_end = VSYSCALL_ADDR + PAGE_SIZE,
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+ .vm_page_prot = PAGE_READONLY_EXEC,
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+ .vm_flags = VM_READ | VM_EXEC,
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+ .vm_ops = &gate_vma_ops,
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+};
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+
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+struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
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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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+#ifdef CONFIG_IA32_EMULATION
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+ if (!mm || mm->context.ia32_compat)
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+ return NULL;
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+#endif
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+ if (vsyscall_mode == NONE)
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+ return NULL;
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+ return &gate_vma;
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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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+int in_gate_area(struct mm_struct *mm, unsigned long addr)
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{
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- long cpu = (long)arg;
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+ struct vm_area_struct *vma = get_gate_vma(mm);
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+
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+ if (!vma)
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+ return 0;
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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 (addr >= vma->vm_start) && (addr < vma->vm_end);
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+}
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- return NOTIFY_DONE;
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+/*
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+ * Use this when you have no reliable mm, typically from interrupt
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+ * context. It is less reliable than using a task's mm and may give
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+ * false positives.
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+ */
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+int in_gate_area_no_mm(unsigned long addr)
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+{
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+ return vsyscall_mode != NONE && (addr & PAGE_MASK) == VSYSCALL_ADDR;
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}
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void __init map_vsyscall(void)
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@@ -331,24 +324,12 @@ void __init map_vsyscall(void)
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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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+ if (vsyscall_mode != NONE)
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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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+
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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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-
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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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-
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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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-
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- cpu_notifier_register_done();
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-
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- return 0;
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-}
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-__initcall(vsyscall_init);
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Linus Torvalds