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1/*
2 * linux/arch/arm/kernel/swp_emulate.c
3 *
4 * Copyright (C) 2009 ARM Limited
5 * __user_* functions adapted from include/asm/uaccess.h
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation.
10 *
11 * Implements emulation of the SWP/SWPB instructions using load-exclusive and
12 * store-exclusive for processors that have them disabled (or future ones that
13 * might not implement them).
14 *
15 * Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>]
16 * Where: Rt = destination
17 * Rt2 = source
18 * Rn = address
19 */
20
21#include <linux/init.h>
22#include <linux/kernel.h>
23#include <linux/proc_fs.h>
24#include <linux/sched.h>
25#include <linux/syscalls.h>
26#include <linux/perf_event.h>
27
28#include <asm/traps.h>
29#include <asm/uaccess.h>
30
31/*
32 * Error-checking SWP macros implemented using ldrex{b}/strex{b}
33 */
34#define __user_swpX_asm(data, addr, res, temp, B) \
35 __asm__ __volatile__( \
36 " mov %2, %1\n" \
37 "0: ldrex"B" %1, [%3]\n" \
38 "1: strex"B" %0, %2, [%3]\n" \
39 " cmp %0, #0\n" \
40 " movne %0, %4\n" \
41 "2:\n" \
42 " .section .fixup,\"ax\"\n" \
43 " .align 2\n" \
44 "3: mov %0, %5\n" \
45 " b 2b\n" \
46 " .previous\n" \
47 " .section __ex_table,\"a\"\n" \
48 " .align 3\n" \
49 " .long 0b, 3b\n" \
50 " .long 1b, 3b\n" \
51 " .previous" \
52 : "=&r" (res), "+r" (data), "=&r" (temp) \
53 : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \
54 : "cc", "memory")
55
56#define __user_swp_asm(data, addr, res, temp) \
57 __user_swpX_asm(data, addr, res, temp, "")
58#define __user_swpb_asm(data, addr, res, temp) \
59 __user_swpX_asm(data, addr, res, temp, "b")
60
61/*
62 * Macros/defines for extracting register numbers from instruction.
63 */
64#define EXTRACT_REG_NUM(instruction, offset) \
65 (((instruction) & (0xf << (offset))) >> (offset))
66#define RN_OFFSET 16
67#define RT_OFFSET 12
68#define RT2_OFFSET 0
69/*
70 * Bit 22 of the instruction encoding distinguishes between
71 * the SWP and SWPB variants (bit set means SWPB).
72 */
73#define TYPE_SWPB (1 << 22)
74
75static unsigned long swpcounter;
76static unsigned long swpbcounter;
77static unsigned long abtcounter;
78static pid_t previous_pid;
79
80#ifdef CONFIG_PROC_FS
81static int proc_read_status(char *page, char **start, off_t off, int count,
82 int *eof, void *data)
83{
84 char *p = page;
85 int len;
86
87 p += sprintf(p, "Emulated SWP:\t\t%lu\n", swpcounter);
88 p += sprintf(p, "Emulated SWPB:\t\t%lu\n", swpbcounter);
89 p += sprintf(p, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
90 if (previous_pid != 0)
91 p += sprintf(p, "Last process:\t\t%d\n", previous_pid);
92
93 len = (p - page) - off;
94 if (len < 0)
95 len = 0;
96
97 *eof = (len <= count) ? 1 : 0;
98 *start = page + off;
99
100 return len;
101}
102#endif
103
104/*
105 * Set up process info to signal segmentation fault - called on access error.
106 */
107static void set_segfault(struct pt_regs *regs, unsigned long addr)
108{
109 siginfo_t info;
110
111 if (find_vma(current->mm, addr) == NULL)
112 info.si_code = SEGV_MAPERR;
113 else
114 info.si_code = SEGV_ACCERR;
115
116 info.si_signo = SIGSEGV;
117 info.si_errno = 0;
118 info.si_addr = (void *) instruction_pointer(regs);
119
120 pr_debug("SWP{B} emulation: access caused memory abort!\n");
121 arm_notify_die("Illegal memory access", regs, &info, 0, 0);
122
123 abtcounter++;
124}
125
126static int emulate_swpX(unsigned int address, unsigned int *data,
127 unsigned int type)
128{
129 unsigned int res = 0;
130
131 if ((type != TYPE_SWPB) && (address & 0x3)) {
132 /* SWP to unaligned address not permitted */
133 pr_debug("SWP instruction on unaligned pointer!\n");
134 return -EFAULT;
135 }
136
137 while (1) {
138 unsigned long temp;
139
140 /*
141 * Barrier required between accessing protected resource and
142 * releasing a lock for it. Legacy code might not have done
143 * this, and we cannot determine that this is not the case
144 * being emulated, so insert always.
145 */
146 smp_mb();
147
148 if (type == TYPE_SWPB)
149 __user_swpb_asm(*data, address, res, temp);
150 else
151 __user_swp_asm(*data, address, res, temp);
152
153 if (likely(res != -EAGAIN) || signal_pending(current))
154 break;
155
156 cond_resched();
157 }
158
159 if (res == 0) {
160 /*
161 * Barrier also required between acquiring a lock for a
162 * protected resource and accessing the resource. Inserted for
163 * same reason as above.
164 */
165 smp_mb();
166
167 if (type == TYPE_SWPB)
168 swpbcounter++;
169 else
170 swpcounter++;
171 }
172
173 return res;
174}
175
176/*
177 * swp_handler logs the id of calling process, dissects the instruction, sanity
178 * checks the memory location, calls emulate_swpX for the actual operation and
179 * deals with fixup/error handling before returning
180 */
181static int swp_handler(struct pt_regs *regs, unsigned int instr)
182{
183 unsigned int address, destreg, data, type;
184 unsigned int res = 0;
185
186 perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
187
188 if (current->pid != previous_pid) {
189 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
190 current->comm, (unsigned long)current->pid);
191 previous_pid = current->pid;
192 }
193
194 address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
195 data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
196 destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
197
198 type = instr & TYPE_SWPB;
199
200 pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
201 EXTRACT_REG_NUM(instr, RN_OFFSET), address,
202 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
203
204 /* Check access in reasonable access range for both SWP and SWPB */
205 if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
206 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
207 (void *)address);
208 res = -EFAULT;
209 } else {
210 res = emulate_swpX(address, &data, type);
211 }
212
213 if (res == 0) {
214 /*
215 * On successful emulation, revert the adjustment to the PC
216 * made in kernel/traps.c in order to resume execution at the
217 * instruction following the SWP{B}.
218 */
219 regs->ARM_pc += 4;
220 regs->uregs[destreg] = data;
221 } else if (res == -EFAULT) {
222 /*
223 * Memory errors do not mean emulation failed.
224 * Set up signal info to return SEGV, then return OK
225 */
226 set_segfault(regs, address);
227 }
228
229 return 0;
230}
231
232/*
233 * Only emulate SWP/SWPB executed in ARM state/User mode.
234 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
235 */
236static struct undef_hook swp_hook = {
237 .instr_mask = 0x0fb00ff0,
238 .instr_val = 0x01000090,
239 .cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
240 .cpsr_val = USR_MODE,
241 .fn = swp_handler
242};
243
244/*
245 * Register handler and create status file in /proc/cpu
246 * Invoked as late_initcall, since not needed before init spawned.
247 */
248static int __init swp_emulation_init(void)
249{
250#ifdef CONFIG_PROC_FS
251 struct proc_dir_entry *res;
252
253 res = create_proc_entry("cpu/swp_emulation", S_IRUGO, NULL);
254
255 if (!res)
256 return -ENOMEM;
257
258 res->read_proc = proc_read_status;
259#endif /* CONFIG_PROC_FS */
260
261 printk(KERN_NOTICE "Registering SWP/SWPB emulation handler\n");
262 register_undef_hook(&swp_hook);
263
264 return 0;
265}
266
267late_initcall(swp_emulation_init);
1/*
2 * linux/arch/arm/kernel/swp_emulate.c
3 *
4 * Copyright (C) 2009 ARM Limited
5 * __user_* functions adapted from include/asm/uaccess.h
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation.
10 *
11 * Implements emulation of the SWP/SWPB instructions using load-exclusive and
12 * store-exclusive for processors that have them disabled (or future ones that
13 * might not implement them).
14 *
15 * Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>]
16 * Where: Rt = destination
17 * Rt2 = source
18 * Rn = address
19 */
20
21#include <linux/init.h>
22#include <linux/kernel.h>
23#include <linux/proc_fs.h>
24#include <linux/seq_file.h>
25#include <linux/sched.h>
26#include <linux/syscalls.h>
27#include <linux/perf_event.h>
28
29#include <asm/opcodes.h>
30#include <asm/system_info.h>
31#include <asm/traps.h>
32#include <linux/uaccess.h>
33
34/*
35 * Error-checking SWP macros implemented using ldrex{b}/strex{b}
36 */
37#define __user_swpX_asm(data, addr, res, temp, B) \
38 __asm__ __volatile__( \
39 "0: ldrex"B" %2, [%3]\n" \
40 "1: strex"B" %0, %1, [%3]\n" \
41 " cmp %0, #0\n" \
42 " moveq %1, %2\n" \
43 " movne %0, %4\n" \
44 "2:\n" \
45 " .section .text.fixup,\"ax\"\n" \
46 " .align 2\n" \
47 "3: mov %0, %5\n" \
48 " b 2b\n" \
49 " .previous\n" \
50 " .section __ex_table,\"a\"\n" \
51 " .align 3\n" \
52 " .long 0b, 3b\n" \
53 " .long 1b, 3b\n" \
54 " .previous" \
55 : "=&r" (res), "+r" (data), "=&r" (temp) \
56 : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \
57 : "cc", "memory")
58
59#define __user_swp_asm(data, addr, res, temp) \
60 __user_swpX_asm(data, addr, res, temp, "")
61#define __user_swpb_asm(data, addr, res, temp) \
62 __user_swpX_asm(data, addr, res, temp, "b")
63
64/*
65 * Macros/defines for extracting register numbers from instruction.
66 */
67#define EXTRACT_REG_NUM(instruction, offset) \
68 (((instruction) & (0xf << (offset))) >> (offset))
69#define RN_OFFSET 16
70#define RT_OFFSET 12
71#define RT2_OFFSET 0
72/*
73 * Bit 22 of the instruction encoding distinguishes between
74 * the SWP and SWPB variants (bit set means SWPB).
75 */
76#define TYPE_SWPB (1 << 22)
77
78static unsigned long swpcounter;
79static unsigned long swpbcounter;
80static unsigned long abtcounter;
81static pid_t previous_pid;
82
83#ifdef CONFIG_PROC_FS
84static int proc_status_show(struct seq_file *m, void *v)
85{
86 seq_printf(m, "Emulated SWP:\t\t%lu\n", swpcounter);
87 seq_printf(m, "Emulated SWPB:\t\t%lu\n", swpbcounter);
88 seq_printf(m, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
89 if (previous_pid != 0)
90 seq_printf(m, "Last process:\t\t%d\n", previous_pid);
91 return 0;
92}
93
94static int proc_status_open(struct inode *inode, struct file *file)
95{
96 return single_open(file, proc_status_show, PDE_DATA(inode));
97}
98
99static const struct file_operations proc_status_fops = {
100 .open = proc_status_open,
101 .read = seq_read,
102 .llseek = seq_lseek,
103 .release = single_release,
104};
105#endif
106
107/*
108 * Set up process info to signal segmentation fault - called on access error.
109 */
110static void set_segfault(struct pt_regs *regs, unsigned long addr)
111{
112 siginfo_t info;
113
114 down_read(¤t->mm->mmap_sem);
115 if (find_vma(current->mm, addr) == NULL)
116 info.si_code = SEGV_MAPERR;
117 else
118 info.si_code = SEGV_ACCERR;
119 up_read(¤t->mm->mmap_sem);
120
121 info.si_signo = SIGSEGV;
122 info.si_errno = 0;
123 info.si_addr = (void *) instruction_pointer(regs);
124
125 pr_debug("SWP{B} emulation: access caused memory abort!\n");
126 arm_notify_die("Illegal memory access", regs, &info, 0, 0);
127
128 abtcounter++;
129}
130
131static int emulate_swpX(unsigned int address, unsigned int *data,
132 unsigned int type)
133{
134 unsigned int res = 0;
135
136 if ((type != TYPE_SWPB) && (address & 0x3)) {
137 /* SWP to unaligned address not permitted */
138 pr_debug("SWP instruction on unaligned pointer!\n");
139 return -EFAULT;
140 }
141
142 while (1) {
143 unsigned long temp;
144 unsigned int __ua_flags;
145
146 __ua_flags = uaccess_save_and_enable();
147 if (type == TYPE_SWPB)
148 __user_swpb_asm(*data, address, res, temp);
149 else
150 __user_swp_asm(*data, address, res, temp);
151 uaccess_restore(__ua_flags);
152
153 if (likely(res != -EAGAIN) || signal_pending(current))
154 break;
155
156 cond_resched();
157 }
158
159 if (res == 0) {
160 if (type == TYPE_SWPB)
161 swpbcounter++;
162 else
163 swpcounter++;
164 }
165
166 return res;
167}
168
169/*
170 * swp_handler logs the id of calling process, dissects the instruction, sanity
171 * checks the memory location, calls emulate_swpX for the actual operation and
172 * deals with fixup/error handling before returning
173 */
174static int swp_handler(struct pt_regs *regs, unsigned int instr)
175{
176 unsigned int address, destreg, data, type;
177 unsigned int res = 0;
178
179 perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
180
181 res = arm_check_condition(instr, regs->ARM_cpsr);
182 switch (res) {
183 case ARM_OPCODE_CONDTEST_PASS:
184 break;
185 case ARM_OPCODE_CONDTEST_FAIL:
186 /* Condition failed - return to next instruction */
187 regs->ARM_pc += 4;
188 return 0;
189 case ARM_OPCODE_CONDTEST_UNCOND:
190 /* If unconditional encoding - not a SWP, undef */
191 return -EFAULT;
192 default:
193 return -EINVAL;
194 }
195
196 if (current->pid != previous_pid) {
197 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
198 current->comm, (unsigned long)current->pid);
199 previous_pid = current->pid;
200 }
201
202 address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
203 data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
204 destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
205
206 type = instr & TYPE_SWPB;
207
208 pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
209 EXTRACT_REG_NUM(instr, RN_OFFSET), address,
210 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
211
212 /* Check access in reasonable access range for both SWP and SWPB */
213 if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
214 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
215 (void *)address);
216 res = -EFAULT;
217 } else {
218 res = emulate_swpX(address, &data, type);
219 }
220
221 if (res == 0) {
222 /*
223 * On successful emulation, revert the adjustment to the PC
224 * made in kernel/traps.c in order to resume execution at the
225 * instruction following the SWP{B}.
226 */
227 regs->ARM_pc += 4;
228 regs->uregs[destreg] = data;
229 } else if (res == -EFAULT) {
230 /*
231 * Memory errors do not mean emulation failed.
232 * Set up signal info to return SEGV, then return OK
233 */
234 set_segfault(regs, address);
235 }
236
237 return 0;
238}
239
240/*
241 * Only emulate SWP/SWPB executed in ARM state/User mode.
242 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
243 */
244static struct undef_hook swp_hook = {
245 .instr_mask = 0x0fb00ff0,
246 .instr_val = 0x01000090,
247 .cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
248 .cpsr_val = USR_MODE,
249 .fn = swp_handler
250};
251
252/*
253 * Register handler and create status file in /proc/cpu
254 * Invoked as late_initcall, since not needed before init spawned.
255 */
256static int __init swp_emulation_init(void)
257{
258 if (cpu_architecture() < CPU_ARCH_ARMv7)
259 return 0;
260
261#ifdef CONFIG_PROC_FS
262 if (!proc_create("cpu/swp_emulation", S_IRUGO, NULL, &proc_status_fops))
263 return -ENOMEM;
264#endif /* CONFIG_PROC_FS */
265
266 pr_notice("Registering SWP/SWPB emulation handler\n");
267 register_undef_hook(&swp_hook);
268
269 return 0;
270}
271
272late_initcall(swp_emulation_init);