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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 ".arch armv7-a\n" \
38 "0: ldrex"B" %2, [%3]\n" \
39 "1: strex"B" %0, %1, [%3]\n" \
40 " cmp %0, #0\n" \
41 " moveq %1, %2\n" \
42 " movne %0, %4\n" \
43 "2:\n" \
44 " .section .text.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#endif
93
94/*
95 * Set up process info to signal segmentation fault - called on access error.
96 */
97static void set_segfault(struct pt_regs *regs, unsigned long addr)
98{
99 int si_code;
100
101 mmap_read_lock(current->mm);
102 if (find_vma(current->mm, addr) == NULL)
103 si_code = SEGV_MAPERR;
104 else
105 si_code = SEGV_ACCERR;
106 mmap_read_unlock(current->mm);
107
108 pr_debug("SWP{B} emulation: access caused memory abort!\n");
109 arm_notify_die("Illegal memory access", regs,
110 SIGSEGV, si_code,
111 (void __user *)instruction_pointer(regs),
112 0, 0);
113
114 abtcounter++;
115}
116
117static int emulate_swpX(unsigned int address, unsigned int *data,
118 unsigned int type)
119{
120 unsigned int res = 0;
121
122 if ((type != TYPE_SWPB) && (address & 0x3)) {
123 /* SWP to unaligned address not permitted */
124 pr_debug("SWP instruction on unaligned pointer!\n");
125 return -EFAULT;
126 }
127
128 while (1) {
129 unsigned long temp;
130 unsigned int __ua_flags;
131
132 __ua_flags = uaccess_save_and_enable();
133 if (type == TYPE_SWPB)
134 __user_swpb_asm(*data, address, res, temp);
135 else
136 __user_swp_asm(*data, address, res, temp);
137 uaccess_restore(__ua_flags);
138
139 if (likely(res != -EAGAIN) || signal_pending(current))
140 break;
141
142 cond_resched();
143 }
144
145 if (res == 0) {
146 if (type == TYPE_SWPB)
147 swpbcounter++;
148 else
149 swpcounter++;
150 }
151
152 return res;
153}
154
155/*
156 * swp_handler logs the id of calling process, dissects the instruction, sanity
157 * checks the memory location, calls emulate_swpX for the actual operation and
158 * deals with fixup/error handling before returning
159 */
160static int swp_handler(struct pt_regs *regs, unsigned int instr)
161{
162 unsigned int address, destreg, data, type;
163 unsigned int res = 0;
164
165 perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
166
167 res = arm_check_condition(instr, regs->ARM_cpsr);
168 switch (res) {
169 case ARM_OPCODE_CONDTEST_PASS:
170 break;
171 case ARM_OPCODE_CONDTEST_FAIL:
172 /* Condition failed - return to next instruction */
173 regs->ARM_pc += 4;
174 return 0;
175 case ARM_OPCODE_CONDTEST_UNCOND:
176 /* If unconditional encoding - not a SWP, undef */
177 return -EFAULT;
178 default:
179 return -EINVAL;
180 }
181
182 if (current->pid != previous_pid) {
183 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
184 current->comm, (unsigned long)current->pid);
185 previous_pid = current->pid;
186 }
187
188 address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
189 data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
190 destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
191
192 type = instr & TYPE_SWPB;
193
194 pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
195 EXTRACT_REG_NUM(instr, RN_OFFSET), address,
196 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
197
198 /* Check access in reasonable access range for both SWP and SWPB */
199 if (!access_ok((void __user *)(address & ~3), 4)) {
200 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
201 (void *)address);
202 res = -EFAULT;
203 } else {
204 res = emulate_swpX(address, &data, type);
205 }
206
207 if (res == 0) {
208 /*
209 * On successful emulation, revert the adjustment to the PC
210 * made in kernel/traps.c in order to resume execution at the
211 * instruction following the SWP{B}.
212 */
213 regs->ARM_pc += 4;
214 regs->uregs[destreg] = data;
215 } else if (res == -EFAULT) {
216 /*
217 * Memory errors do not mean emulation failed.
218 * Set up signal info to return SEGV, then return OK
219 */
220 set_segfault(regs, address);
221 }
222
223 return 0;
224}
225
226/*
227 * Only emulate SWP/SWPB executed in ARM state/User mode.
228 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
229 */
230static struct undef_hook swp_hook = {
231 .instr_mask = 0x0fb00ff0,
232 .instr_val = 0x01000090,
233 .cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
234 .cpsr_val = USR_MODE,
235 .fn = swp_handler
236};
237
238/*
239 * Register handler and create status file in /proc/cpu
240 * Invoked as late_initcall, since not needed before init spawned.
241 */
242static int __init swp_emulation_init(void)
243{
244 if (cpu_architecture() < CPU_ARCH_ARMv7)
245 return 0;
246
247#ifdef CONFIG_PROC_FS
248 if (!proc_create_single("cpu/swp_emulation", S_IRUGO, NULL,
249 proc_status_show))
250 return -ENOMEM;
251#endif /* CONFIG_PROC_FS */
252
253 pr_notice("Registering SWP/SWPB emulation handler\n");
254 register_undef_hook(&swp_hook);
255
256 return 0;
257}
258
259late_initcall(swp_emulation_init);