summaryrefslogtreecommitdiffstats
path: root/arch/x86/kernel/vsyscall_64.c
blob: dda7dff9cef7e624be6239ca463789e09eedd200 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
/*
 *  Copyright (C) 2001 Andrea Arcangeli <andrea@suse.de> SuSE
 *  Copyright 2003 Andi Kleen, SuSE Labs.
 *
 *  [ NOTE: this mechanism is now deprecated in favor of the vDSO. ]
 *
 *  Thanks to hpa@transmeta.com for some useful hint.
 *  Special thanks to Ingo Molnar for his early experience with
 *  a different vsyscall implementation for Linux/IA32 and for the name.
 *
 *  vsyscall 1 is located at -10Mbyte, vsyscall 2 is located
 *  at virtual address -10Mbyte+1024bytes etc... There are at max 4
 *  vsyscalls. One vsyscall can reserve more than 1 slot to avoid
 *  jumping out of line if necessary. We cannot add more with this
 *  mechanism because older kernels won't return -ENOSYS.
 *
 *  Note: the concept clashes with user mode linux.  UML users should
 *  use the vDSO.
 */

/* Disable profiling for userspace code: */
#define DISABLE_BRANCH_PROFILING

#include <linux/time.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/timer.h>
#include <linux/seqlock.h>
#include <linux/jiffies.h>
#include <linux/sysctl.h>
#include <linux/clocksource.h>
#include <linux/getcpu.h>
#include <linux/cpu.h>
#include <linux/smp.h>
#include <linux/notifier.h>
#include <linux/syscalls.h>
#include <linux/ratelimit.h>

#include <asm/vsyscall.h>
#include <asm/pgtable.h>
#include <asm/compat.h>
#include <asm/page.h>
#include <asm/unistd.h>
#include <asm/fixmap.h>
#include <asm/errno.h>
#include <asm/io.h>
#include <asm/segment.h>
#include <asm/desc.h>
#include <asm/topology.h>
#include <asm/vgtod.h>
#include <asm/traps.h>

DEFINE_VVAR(int, vgetcpu_mode);
DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data) =
{
	.lock = __SEQLOCK_UNLOCKED(__vsyscall_gtod_data.lock),
};

void update_vsyscall_tz(void)
{
	unsigned long flags;

	write_seqlock_irqsave(&vsyscall_gtod_data.lock, flags);
	/* sys_tz has changed */
	vsyscall_gtod_data.sys_tz = sys_tz;
	write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
}

void update_vsyscall(struct timespec *wall_time, struct timespec *wtm,
			struct clocksource *clock, u32 mult)
{
	unsigned long flags;

	write_seqlock_irqsave(&vsyscall_gtod_data.lock, flags);

	/* copy vsyscall data */
	vsyscall_gtod_data.clock.vclock_mode	= clock->archdata.vclock_mode;
	vsyscall_gtod_data.clock.cycle_last	= clock->cycle_last;
	vsyscall_gtod_data.clock.mask		= clock->mask;
	vsyscall_gtod_data.clock.mult		= mult;
	vsyscall_gtod_data.clock.shift		= clock->shift;
	vsyscall_gtod_data.wall_time_sec	= wall_time->tv_sec;
	vsyscall_gtod_data.wall_time_nsec	= wall_time->tv_nsec;
	vsyscall_gtod_data.wall_to_monotonic	= *wtm;
	vsyscall_gtod_data.wall_time_coarse	= __current_kernel_time();

	write_sequnlock_irqrestore(&vsyscall_gtod_data.lock, flags);
}

static void warn_bad_vsyscall(const char *level, struct pt_regs *regs,
			      const char *message)
{
	static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL, DEFAULT_RATELIMIT_BURST);
	struct task_struct *tsk;

	if (!show_unhandled_signals || !__ratelimit(&rs))
		return;

	tsk = current;

	printk("%s%s[%d] %s ip:%lx cs:%lx sp:%lx ax:%lx si:%lx di:%lx\n",
	       level, tsk->comm, task_pid_nr(tsk),
	       message, regs->ip - 2, 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_START)
		return -EINVAL;

	nr = (addr & 0xC00UL) >> 10;
	if (nr >= 3)
		return -EINVAL;

	return nr;
}

void dotraplinkage do_emulate_vsyscall(struct pt_regs *regs, long error_code)
{
	struct task_struct *tsk;
	unsigned long caller;
	int vsyscall_nr;
	long ret;

	local_irq_enable();

	/*
	 * Real 64-bit user mode code has cs == __USER_CS.  Anything else
	 * is bogus.
	 */
	if (regs->cs != __USER_CS) {
		/*
		 * If we trapped from kernel mode, we might as well OOPS now
		 * instead of returning to some random address and OOPSing
		 * then.
		 */
		BUG_ON(!user_mode(regs));

		/* Compat mode and non-compat 32-bit CS should both segfault. */
		warn_bad_vsyscall(KERN_WARNING, regs,
				  "illegal int 0xcc from 32-bit mode");
		goto sigsegv;
	}

	/*
	 * x86-ism here: regs->ip points to the instruction after the int 0xcc,
	 * and int 0xcc is two bytes long.
	 */
	vsyscall_nr = addr_to_vsyscall_nr(regs->ip - 2);
	if (vsyscall_nr < 0) {
		warn_bad_vsyscall(KERN_WARNING, regs,
				  "illegal int 0xcc (exploit attempt?)");
		goto sigsegv;
	}

	if (get_user(caller, (unsigned long __user *)regs->sp) != 0) {
		warn_bad_vsyscall(KERN_WARNING, regs, "int 0xcc with bad stack (exploit attempt?)");
		goto sigsegv;
	}

	tsk = current;
	if (seccomp_mode(&tsk->seccomp))
		do_exit(SIGKILL);

	switch (vsyscall_nr) {
	case 0:
		ret = sys_gettimeofday(
			(struct timeval __user *)regs->di,
			(struct timezone __user *)regs->si);
		break;

	case 1:
		ret = sys_time((time_t __user *)regs->di);
		break;

	case 2:
		ret = sys_getcpu((unsigned __user *)regs->di,
				 (unsigned __user *)regs->si,
				 0);
		break;
	}

	if (ret == -EFAULT) {
		/*
		 * Bad news -- userspace fed a bad pointer to a vsyscall.
		 *
		 * With a real vsyscall, that would have caused SIGSEGV.
		 * To make writing reliable exploits using the emulated
		 * vsyscalls harder, generate SIGSEGV here as well.
		 */
		warn_bad_vsyscall(KERN_INFO, regs,
				  "vsyscall fault (exploit attempt?)");
		goto sigsegv;
	}

	regs->ax = ret;

	/* Emulate a ret instruction. */
	regs->ip = caller;
	regs->sp += 8;

	local_irq_disable();
	return;

sigsegv:
	regs->ip -= 2;  /* The faulting instruction should be the int 0xcc. */
	force_sig(SIGSEGV, current);
	local_irq_disable();
}

/*
 * Assume __initcall executes before all user space. Hopefully kmod
 * doesn't violate that. We'll find out if it does.
 */
static void __cpuinit vsyscall_set_cpu(int cpu)
{
	unsigned long d;
	unsigned long node = 0;
#ifdef CONFIG_NUMA
	node = cpu_to_node(cpu);
#endif
	if (cpu_has(&cpu_data(cpu), X86_FEATURE_RDTSCP))
		write_rdtscp_aux((node << 12) | cpu);

	/*
	 * Store cpu number in limit so that it can be loaded quickly
	 * in user space in vgetcpu. (12 bits for the CPU and 8 bits for the node)
	 */
	d = 0x0f40000000000ULL;
	d |= cpu;
	d |= (node & 0xf) << 12;
	d |= (node >> 4) << 48;

	write_gdt_entry(get_cpu_gdt_table(cpu), GDT_ENTRY_PER_CPU, &d, DESCTYPE_S);
}

static void __cpuinit cpu_vsyscall_init(void *arg)
{
	/* preemption should be already off */
	vsyscall_set_cpu(raw_smp_processor_id());
}

static int __cpuinit
cpu_vsyscall_notifier(struct notifier_block *n, unsigned long action, void *arg)
{
	long cpu = (long)arg;

	if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN)
		smp_call_function_single(cpu, cpu_vsyscall_init, NULL, 1);

	return NOTIFY_DONE;
}

void __init map_vsyscall(void)
{
	extern char __vsyscall_0;
	unsigned long physaddr_page0 = __pa_symbol(&__vsyscall_0);
	extern char __vvar_page;
	unsigned long physaddr_vvar_page = __pa_symbol(&__vvar_page);

	/* Note that VSYSCALL_MAPPED_PAGES must agree with the code below. */
	__set_fixmap(VSYSCALL_FIRST_PAGE, physaddr_page0, PAGE_KERNEL_VSYSCALL);
	__set_fixmap(VVAR_PAGE, physaddr_vvar_page, PAGE_KERNEL_VVAR);
	BUILD_BUG_ON((unsigned long)__fix_to_virt(VVAR_PAGE) != (unsigned long)VVAR_ADDRESS);
}

static int __init vsyscall_init(void)
{
	BUG_ON(VSYSCALL_ADDR(0) != __fix_to_virt(VSYSCALL_FIRST_PAGE));

	on_each_cpu(cpu_vsyscall_init, NULL, 1);
	/* notifier priority > KVM */
	hotcpu_notifier(cpu_vsyscall_notifier, 30);

	return 0;
}
__initcall(vsyscall_init);