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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * linux/arch/arm/kernel/swp_emulate.c
4 *
5 * Copyright (C) 2009 ARM Limited
6 * __user_* functions adapted from include/asm/uaccess.h
7 *
8 * Implements emulation of the SWP/SWPB instructions using load-exclusive and
9 * store-exclusive for processors that have them disabled (or future ones that
10 * might not implement them).
11 *
12 * Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>]
13 * Where: Rt = destination
14 * Rt2 = source
15 * Rn = address
16 */
17
18#include <linux/init.h>
19#include <linux/kernel.h>
20#include <linux/proc_fs.h>
21#include <linux/seq_file.h>
22#include <linux/sched.h>
23#include <linux/sched/mm.h>
24#include <linux/syscalls.h>
25#include <linux/perf_event.h>
26
27#include <asm/opcodes.h>
28#include <asm/system_info.h>
29#include <asm/traps.h>
30#include <linux/uaccess.h>
31
32/*
33 * Error-checking SWP macros implemented using ldrex{b}/strex{b}
34 */
35#define __user_swpX_asm(data, addr, res, temp, B) \
36 __asm__ __volatile__( \
37 "0: ldrex"B" %2, [%3]\n" \
38 "1: strex"B" %0, %1, [%3]\n" \
39 " cmp %0, #0\n" \
40 " moveq %1, %2\n" \
41 " movne %0, %4\n" \
42 "2:\n" \
43 " .section .text.fixup,\"ax\"\n" \
44 " .align 2\n" \
45 "3: mov %0, %5\n" \
46 " b 2b\n" \
47 " .previous\n" \
48 " .section __ex_table,\"a\"\n" \
49 " .align 3\n" \
50 " .long 0b, 3b\n" \
51 " .long 1b, 3b\n" \
52 " .previous" \
53 : "=&r" (res), "+r" (data), "=&r" (temp) \
54 : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \
55 : "cc", "memory")
56
57#define __user_swp_asm(data, addr, res, temp) \
58 __user_swpX_asm(data, addr, res, temp, "")
59#define __user_swpb_asm(data, addr, res, temp) \
60 __user_swpX_asm(data, addr, res, temp, "b")
61
62/*
63 * Macros/defines for extracting register numbers from instruction.
64 */
65#define EXTRACT_REG_NUM(instruction, offset) \
66 (((instruction) & (0xf << (offset))) >> (offset))
67#define RN_OFFSET 16
68#define RT_OFFSET 12
69#define RT2_OFFSET 0
70/*
71 * Bit 22 of the instruction encoding distinguishes between
72 * the SWP and SWPB variants (bit set means SWPB).
73 */
74#define TYPE_SWPB (1 << 22)
75
76static unsigned long swpcounter;
77static unsigned long swpbcounter;
78static unsigned long abtcounter;
79static pid_t previous_pid;
80
81#ifdef CONFIG_PROC_FS
82static int proc_status_show(struct seq_file *m, void *v)
83{
84 seq_printf(m, "Emulated SWP:\t\t%lu\n", swpcounter);
85 seq_printf(m, "Emulated SWPB:\t\t%lu\n", swpbcounter);
86 seq_printf(m, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
87 if (previous_pid != 0)
88 seq_printf(m, "Last process:\t\t%d\n", previous_pid);
89 return 0;
90}
91#endif
92
93/*
94 * Set up process info to signal segmentation fault - called on access error.
95 */
96static void set_segfault(struct pt_regs *regs, unsigned long addr)
97{
98 int si_code;
99
100 mmap_read_lock(current->mm);
101 if (find_vma(current->mm, addr) == NULL)
102 si_code = SEGV_MAPERR;
103 else
104 si_code = SEGV_ACCERR;
105 mmap_read_unlock(current->mm);
106
107 pr_debug("SWP{B} emulation: access caused memory abort!\n");
108 arm_notify_die("Illegal memory access", regs,
109 SIGSEGV, si_code,
110 (void __user *)instruction_pointer(regs),
111 0, 0);
112
113 abtcounter++;
114}
115
116static int emulate_swpX(unsigned int address, unsigned int *data,
117 unsigned int type)
118{
119 unsigned int res = 0;
120
121 if ((type != TYPE_SWPB) && (address & 0x3)) {
122 /* SWP to unaligned address not permitted */
123 pr_debug("SWP instruction on unaligned pointer!\n");
124 return -EFAULT;
125 }
126
127 while (1) {
128 unsigned long temp;
129 unsigned int __ua_flags;
130
131 __ua_flags = uaccess_save_and_enable();
132 if (type == TYPE_SWPB)
133 __user_swpb_asm(*data, address, res, temp);
134 else
135 __user_swp_asm(*data, address, res, temp);
136 uaccess_restore(__ua_flags);
137
138 if (likely(res != -EAGAIN) || signal_pending(current))
139 break;
140
141 cond_resched();
142 }
143
144 if (res == 0) {
145 if (type == TYPE_SWPB)
146 swpbcounter++;
147 else
148 swpcounter++;
149 }
150
151 return res;
152}
153
154/*
155 * swp_handler logs the id of calling process, dissects the instruction, sanity
156 * checks the memory location, calls emulate_swpX for the actual operation and
157 * deals with fixup/error handling before returning
158 */
159static int swp_handler(struct pt_regs *regs, unsigned int instr)
160{
161 unsigned int address, destreg, data, type;
162 unsigned int res = 0;
163
164 perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
165
166 res = arm_check_condition(instr, regs->ARM_cpsr);
167 switch (res) {
168 case ARM_OPCODE_CONDTEST_PASS:
169 break;
170 case ARM_OPCODE_CONDTEST_FAIL:
171 /* Condition failed - return to next instruction */
172 regs->ARM_pc += 4;
173 return 0;
174 case ARM_OPCODE_CONDTEST_UNCOND:
175 /* If unconditional encoding - not a SWP, undef */
176 return -EFAULT;
177 default:
178 return -EINVAL;
179 }
180
181 if (current->pid != previous_pid) {
182 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
183 current->comm, (unsigned long)current->pid);
184 previous_pid = current->pid;
185 }
186
187 address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
188 data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
189 destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
190
191 type = instr & TYPE_SWPB;
192
193 pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
194 EXTRACT_REG_NUM(instr, RN_OFFSET), address,
195 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
196
197 /* Check access in reasonable access range for both SWP and SWPB */
198 if (!access_ok((address & ~3), 4)) {
199 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
200 (void *)address);
201 res = -EFAULT;
202 } else {
203 res = emulate_swpX(address, &data, type);
204 }
205
206 if (res == 0) {
207 /*
208 * On successful emulation, revert the adjustment to the PC
209 * made in kernel/traps.c in order to resume execution at the
210 * instruction following the SWP{B}.
211 */
212 regs->ARM_pc += 4;
213 regs->uregs[destreg] = data;
214 } else if (res == -EFAULT) {
215 /*
216 * Memory errors do not mean emulation failed.
217 * Set up signal info to return SEGV, then return OK
218 */
219 set_segfault(regs, address);
220 }
221
222 return 0;
223}
224
225/*
226 * Only emulate SWP/SWPB executed in ARM state/User mode.
227 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
228 */
229static struct undef_hook swp_hook = {
230 .instr_mask = 0x0fb00ff0,
231 .instr_val = 0x01000090,
232 .cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
233 .cpsr_val = USR_MODE,
234 .fn = swp_handler
235};
236
237/*
238 * Register handler and create status file in /proc/cpu
239 * Invoked as late_initcall, since not needed before init spawned.
240 */
241static int __init swp_emulation_init(void)
242{
243 if (cpu_architecture() < CPU_ARCH_ARMv7)
244 return 0;
245
246#ifdef CONFIG_PROC_FS
247 if (!proc_create_single("cpu/swp_emulation", S_IRUGO, NULL,
248 proc_status_show))
249 return -ENOMEM;
250#endif /* CONFIG_PROC_FS */
251
252 pr_notice("Registering SWP/SWPB emulation handler\n");
253 register_undef_hook(&swp_hook);
254
255 return 0;
256}
257
258late_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/traps.h>
31#include <asm/uaccess.h>
32
33/*
34 * Error-checking SWP macros implemented using ldrex{b}/strex{b}
35 */
36#define __user_swpX_asm(data, addr, res, temp, B) \
37 __asm__ __volatile__( \
38 " mov %2, %1\n" \
39 "0: ldrex"B" %1, [%3]\n" \
40 "1: strex"B" %0, %2, [%3]\n" \
41 " cmp %0, #0\n" \
42 " movne %0, %4\n" \
43 "2:\n" \
44 " .section .fixup,\"ax\"\n" \
45 " .align 2\n" \
46 "3: mov %0, %5\n" \
47 " b 2b\n" \
48 " .previous\n" \
49 " .section __ex_table,\"a\"\n" \
50 " .align 3\n" \
51 " .long 0b, 3b\n" \
52 " .long 1b, 3b\n" \
53 " .previous" \
54 : "=&r" (res), "+r" (data), "=&r" (temp) \
55 : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \
56 : "cc", "memory")
57
58#define __user_swp_asm(data, addr, res, temp) \
59 __user_swpX_asm(data, addr, res, temp, "")
60#define __user_swpb_asm(data, addr, res, temp) \
61 __user_swpX_asm(data, addr, res, temp, "b")
62
63/*
64 * Macros/defines for extracting register numbers from instruction.
65 */
66#define EXTRACT_REG_NUM(instruction, offset) \
67 (((instruction) & (0xf << (offset))) >> (offset))
68#define RN_OFFSET 16
69#define RT_OFFSET 12
70#define RT2_OFFSET 0
71/*
72 * Bit 22 of the instruction encoding distinguishes between
73 * the SWP and SWPB variants (bit set means SWPB).
74 */
75#define TYPE_SWPB (1 << 22)
76
77static unsigned long swpcounter;
78static unsigned long swpbcounter;
79static unsigned long abtcounter;
80static pid_t previous_pid;
81
82#ifdef CONFIG_PROC_FS
83static int proc_status_show(struct seq_file *m, void *v)
84{
85 seq_printf(m, "Emulated SWP:\t\t%lu\n", swpcounter);
86 seq_printf(m, "Emulated SWPB:\t\t%lu\n", swpbcounter);
87 seq_printf(m, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
88 if (previous_pid != 0)
89 seq_printf(m, "Last process:\t\t%d\n", previous_pid);
90 return 0;
91}
92
93static int proc_status_open(struct inode *inode, struct file *file)
94{
95 return single_open(file, proc_status_show, PDE_DATA(inode));
96}
97
98static const struct file_operations proc_status_fops = {
99 .open = proc_status_open,
100 .read = seq_read,
101 .llseek = seq_lseek,
102 .release = single_release,
103};
104#endif
105
106/*
107 * Set up process info to signal segmentation fault - called on access error.
108 */
109static void set_segfault(struct pt_regs *regs, unsigned long addr)
110{
111 siginfo_t info;
112
113 down_read(¤t->mm->mmap_sem);
114 if (find_vma(current->mm, addr) == NULL)
115 info.si_code = SEGV_MAPERR;
116 else
117 info.si_code = SEGV_ACCERR;
118 up_read(¤t->mm->mmap_sem);
119
120 info.si_signo = SIGSEGV;
121 info.si_errno = 0;
122 info.si_addr = (void *) instruction_pointer(regs);
123
124 pr_debug("SWP{B} emulation: access caused memory abort!\n");
125 arm_notify_die("Illegal memory access", regs, &info, 0, 0);
126
127 abtcounter++;
128}
129
130static int emulate_swpX(unsigned int address, unsigned int *data,
131 unsigned int type)
132{
133 unsigned int res = 0;
134
135 if ((type != TYPE_SWPB) && (address & 0x3)) {
136 /* SWP to unaligned address not permitted */
137 pr_debug("SWP instruction on unaligned pointer!\n");
138 return -EFAULT;
139 }
140
141 while (1) {
142 unsigned long temp;
143
144 /*
145 * Barrier required between accessing protected resource and
146 * releasing a lock for it. Legacy code might not have done
147 * this, and we cannot determine that this is not the case
148 * being emulated, so insert always.
149 */
150 smp_mb();
151
152 if (type == TYPE_SWPB)
153 __user_swpb_asm(*data, address, res, temp);
154 else
155 __user_swp_asm(*data, address, res, temp);
156
157 if (likely(res != -EAGAIN) || signal_pending(current))
158 break;
159
160 cond_resched();
161 }
162
163 if (res == 0) {
164 /*
165 * Barrier also required between acquiring a lock for a
166 * protected resource and accessing the resource. Inserted for
167 * same reason as above.
168 */
169 smp_mb();
170
171 if (type == TYPE_SWPB)
172 swpbcounter++;
173 else
174 swpcounter++;
175 }
176
177 return res;
178}
179
180/*
181 * swp_handler logs the id of calling process, dissects the instruction, sanity
182 * checks the memory location, calls emulate_swpX for the actual operation and
183 * deals with fixup/error handling before returning
184 */
185static int swp_handler(struct pt_regs *regs, unsigned int instr)
186{
187 unsigned int address, destreg, data, type;
188 unsigned int res = 0;
189
190 perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
191
192 res = arm_check_condition(instr, regs->ARM_cpsr);
193 switch (res) {
194 case ARM_OPCODE_CONDTEST_PASS:
195 break;
196 case ARM_OPCODE_CONDTEST_FAIL:
197 /* Condition failed - return to next instruction */
198 regs->ARM_pc += 4;
199 return 0;
200 case ARM_OPCODE_CONDTEST_UNCOND:
201 /* If unconditional encoding - not a SWP, undef */
202 return -EFAULT;
203 default:
204 return -EINVAL;
205 }
206
207 if (current->pid != previous_pid) {
208 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
209 current->comm, (unsigned long)current->pid);
210 previous_pid = current->pid;
211 }
212
213 address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
214 data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
215 destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
216
217 type = instr & TYPE_SWPB;
218
219 pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
220 EXTRACT_REG_NUM(instr, RN_OFFSET), address,
221 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
222
223 /* Check access in reasonable access range for both SWP and SWPB */
224 if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
225 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
226 (void *)address);
227 res = -EFAULT;
228 } else {
229 res = emulate_swpX(address, &data, type);
230 }
231
232 if (res == 0) {
233 /*
234 * On successful emulation, revert the adjustment to the PC
235 * made in kernel/traps.c in order to resume execution at the
236 * instruction following the SWP{B}.
237 */
238 regs->ARM_pc += 4;
239 regs->uregs[destreg] = data;
240 } else if (res == -EFAULT) {
241 /*
242 * Memory errors do not mean emulation failed.
243 * Set up signal info to return SEGV, then return OK
244 */
245 set_segfault(regs, address);
246 }
247
248 return 0;
249}
250
251/*
252 * Only emulate SWP/SWPB executed in ARM state/User mode.
253 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
254 */
255static struct undef_hook swp_hook = {
256 .instr_mask = 0x0fb00ff0,
257 .instr_val = 0x01000090,
258 .cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
259 .cpsr_val = USR_MODE,
260 .fn = swp_handler
261};
262
263/*
264 * Register handler and create status file in /proc/cpu
265 * Invoked as late_initcall, since not needed before init spawned.
266 */
267static int __init swp_emulation_init(void)
268{
269#ifdef CONFIG_PROC_FS
270 if (!proc_create("cpu/swp_emulation", S_IRUGO, NULL, &proc_status_fops))
271 return -ENOMEM;
272#endif /* CONFIG_PROC_FS */
273
274 printk(KERN_NOTICE "Registering SWP/SWPB emulation handler\n");
275 register_undef_hook(&swp_hook);
276
277 return 0;
278}
279
280late_initcall(swp_emulation_init);