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/extable.h>
28 #include <asm/opcodes.h>
29 #include <asm/system_info.h>
30 #include <asm/traps.h>
31 #include <linux/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 "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 " ex_entry 0b, 3b\n" \
50 " ex_entry 1b, 3b\n" \
51 : "=&r" (res), "+r" (data), "=&r" (temp) \
52 : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \
53 : "cc", "memory")
54
55 #define __user_swp_asm(data, addr, res, temp) \
56 __user_swpX_asm(data, addr, res, temp, "")
57 #define __user_swpb_asm(data, addr, res, temp) \
58 __user_swpX_asm(data, addr, res, temp, "b")
59
60 /*
61 * Macros/defines for extracting register numbers from instruction.
62 */
63 #define EXTRACT_REG_NUM(instruction, offset) \
64 (((instruction) & (0xf << (offset))) >> (offset))
65 #define RN_OFFSET 16
66 #define RT_OFFSET 12
67 #define RT2_OFFSET 0
68 /*
69 * Bit 22 of the instruction encoding distinguishes between
70 * the SWP and SWPB variants (bit set means SWPB).
71 */
72 #define TYPE_SWPB (1 << 22)
73
74 static unsigned long swpcounter;
75 static unsigned long swpbcounter;
76 static unsigned long abtcounter;
77 static pid_t previous_pid;
78
79 #ifdef CONFIG_PROC_FS
proc_status_show(struct seq_file * m,void * v)80 static int proc_status_show(struct seq_file *m, void *v)
81 {
82 seq_printf(m, "Emulated SWP:\t\t%lu\n", swpcounter);
83 seq_printf(m, "Emulated SWPB:\t\t%lu\n", swpbcounter);
84 seq_printf(m, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
85 if (previous_pid != 0)
86 seq_printf(m, "Last process:\t\t%d\n", previous_pid);
87 return 0;
88 }
89 #endif
90
91 /*
92 * Set up process info to signal segmentation fault - called on access error.
93 */
set_segfault(struct pt_regs * regs,unsigned long addr)94 static void set_segfault(struct pt_regs *regs, unsigned long addr)
95 {
96 int si_code;
97
98 mmap_read_lock(current->mm);
99 if (find_vma(current->mm, addr) == NULL)
100 si_code = SEGV_MAPERR;
101 else
102 si_code = SEGV_ACCERR;
103 mmap_read_unlock(current->mm);
104
105 pr_debug("SWP{B} emulation: access caused memory abort!\n");
106 arm_notify_die("Illegal memory access", regs,
107 SIGSEGV, si_code,
108 (void __user *)instruction_pointer(regs),
109 0, 0);
110
111 abtcounter++;
112 }
113
emulate_swpX(unsigned int address,unsigned int * data,unsigned int type)114 static int emulate_swpX(unsigned int address, unsigned int *data,
115 unsigned int type)
116 {
117 unsigned int res = 0;
118
119 if ((type != TYPE_SWPB) && (address & 0x3)) {
120 /* SWP to unaligned address not permitted */
121 pr_debug("SWP instruction on unaligned pointer!\n");
122 return -EFAULT;
123 }
124
125 while (1) {
126 unsigned long temp;
127 unsigned int __ua_flags;
128
129 __ua_flags = uaccess_save_and_enable();
130 if (type == TYPE_SWPB)
131 __user_swpb_asm(*data, address, res, temp);
132 else
133 __user_swp_asm(*data, address, res, temp);
134 uaccess_restore(__ua_flags);
135
136 if (likely(res != -EAGAIN) || signal_pending(current))
137 break;
138
139 cond_resched();
140 }
141
142 if (res == 0) {
143 if (type == TYPE_SWPB)
144 swpbcounter++;
145 else
146 swpcounter++;
147 }
148
149 return res;
150 }
151
152 /*
153 * swp_handler logs the id of calling process, dissects the instruction, sanity
154 * checks the memory location, calls emulate_swpX for the actual operation and
155 * deals with fixup/error handling before returning
156 */
swp_handler(struct pt_regs * regs,unsigned int instr)157 static int swp_handler(struct pt_regs *regs, unsigned int instr)
158 {
159 unsigned int address, destreg, data, type;
160 unsigned int res = 0;
161
162 perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
163
164 res = arm_check_condition(instr, regs->ARM_cpsr);
165 switch (res) {
166 case ARM_OPCODE_CONDTEST_PASS:
167 break;
168 case ARM_OPCODE_CONDTEST_FAIL:
169 /* Condition failed - return to next instruction */
170 regs->ARM_pc += 4;
171 return 0;
172 case ARM_OPCODE_CONDTEST_UNCOND:
173 /* If unconditional encoding - not a SWP, undef */
174 return -EFAULT;
175 default:
176 return -EINVAL;
177 }
178
179 if (current->pid != previous_pid) {
180 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
181 current->comm, (unsigned long)current->pid);
182 previous_pid = current->pid;
183 }
184
185 address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
186 data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
187 destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
188
189 type = instr & TYPE_SWPB;
190
191 pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
192 EXTRACT_REG_NUM(instr, RN_OFFSET), address,
193 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
194
195 /* Check access in reasonable access range for both SWP and SWPB */
196 if (!access_ok((void __user *)(address & ~3), 4)) {
197 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
198 (void *)address);
199 res = -EFAULT;
200 } else {
201 res = emulate_swpX(address, &data, type);
202 }
203
204 if (res == 0) {
205 /*
206 * On successful emulation, revert the adjustment to the PC
207 * made in kernel/traps.c in order to resume execution at the
208 * instruction following the SWP{B}.
209 */
210 regs->ARM_pc += 4;
211 regs->uregs[destreg] = data;
212 } else if (res == -EFAULT) {
213 /*
214 * Memory errors do not mean emulation failed.
215 * Set up signal info to return SEGV, then return OK
216 */
217 set_segfault(regs, address);
218 }
219
220 return 0;
221 }
222
223 /*
224 * Only emulate SWP/SWPB executed in ARM state/User mode.
225 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
226 */
227 static struct undef_hook swp_hook = {
228 .instr_mask = 0x0fb00ff0,
229 .instr_val = 0x01000090,
230 .cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
231 .cpsr_val = USR_MODE,
232 .fn = swp_handler
233 };
234
235 /*
236 * Register handler and create status file in /proc/cpu
237 * Invoked as late_initcall, since not needed before init spawned.
238 */
swp_emulation_init(void)239 static int __init swp_emulation_init(void)
240 {
241 if (cpu_architecture() < CPU_ARCH_ARMv7)
242 return 0;
243
244 #ifdef CONFIG_PROC_FS
245 if (!proc_create_single("cpu/swp_emulation", S_IRUGO, NULL,
246 proc_status_show))
247 return -ENOMEM;
248 #endif /* CONFIG_PROC_FS */
249
250 pr_notice("Registering SWP/SWPB emulation handler\n");
251 register_undef_hook(&swp_hook);
252
253 return 0;
254 }
255
256 late_initcall(swp_emulation_init);
257