xref: /linux/arch/arm/kernel/swp_emulate.c (revision 4413e16d9d21673bb5048a2e542f1aaa00015c2e)
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/opcodes.h>
29 #include <asm/traps.h>
30 #include <asm/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 	"	mov		%2, %1\n"			\
38 	"0:	ldrex"B"	%1, [%3]\n"			\
39 	"1:	strex"B"	%0, %2, [%3]\n"			\
40 	"	cmp		%0, #0\n"			\
41 	"	movne		%0, %4\n"			\
42 	"2:\n"							\
43 	"	.section	 .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 
76 static unsigned long swpcounter;
77 static unsigned long swpbcounter;
78 static unsigned long abtcounter;
79 static pid_t         previous_pid;
80 
81 #ifdef CONFIG_PROC_FS
82 static int proc_read_status(char *page, char **start, off_t off, int count,
83 			    int *eof, void *data)
84 {
85 	char *p = page;
86 	int len;
87 
88 	p += sprintf(p, "Emulated SWP:\t\t%lu\n", swpcounter);
89 	p += sprintf(p, "Emulated SWPB:\t\t%lu\n", swpbcounter);
90 	p += sprintf(p, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
91 	if (previous_pid != 0)
92 		p += sprintf(p, "Last process:\t\t%d\n", previous_pid);
93 
94 	len = (p - page) - off;
95 	if (len < 0)
96 		len = 0;
97 
98 	*eof = (len <= count) ? 1 : 0;
99 	*start = page + off;
100 
101 	return len;
102 }
103 #endif
104 
105 /*
106  * Set up process info to signal segmentation fault - called on access error.
107  */
108 static void set_segfault(struct pt_regs *regs, unsigned long addr)
109 {
110 	siginfo_t info;
111 
112 	if (find_vma(current->mm, addr) == NULL)
113 		info.si_code = SEGV_MAPERR;
114 	else
115 		info.si_code = SEGV_ACCERR;
116 
117 	info.si_signo = SIGSEGV;
118 	info.si_errno = 0;
119 	info.si_addr  = (void *) instruction_pointer(regs);
120 
121 	pr_debug("SWP{B} emulation: access caused memory abort!\n");
122 	arm_notify_die("Illegal memory access", regs, &info, 0, 0);
123 
124 	abtcounter++;
125 }
126 
127 static int emulate_swpX(unsigned int address, unsigned int *data,
128 			unsigned int type)
129 {
130 	unsigned int res = 0;
131 
132 	if ((type != TYPE_SWPB) && (address & 0x3)) {
133 		/* SWP to unaligned address not permitted */
134 		pr_debug("SWP instruction on unaligned pointer!\n");
135 		return -EFAULT;
136 	}
137 
138 	while (1) {
139 		unsigned long temp;
140 
141 		/*
142 		 * Barrier required between accessing protected resource and
143 		 * releasing a lock for it. Legacy code might not have done
144 		 * this, and we cannot determine that this is not the case
145 		 * being emulated, so insert always.
146 		 */
147 		smp_mb();
148 
149 		if (type == TYPE_SWPB)
150 			__user_swpb_asm(*data, address, res, temp);
151 		else
152 			__user_swp_asm(*data, address, res, temp);
153 
154 		if (likely(res != -EAGAIN) || signal_pending(current))
155 			break;
156 
157 		cond_resched();
158 	}
159 
160 	if (res == 0) {
161 		/*
162 		 * Barrier also required between acquiring a lock for a
163 		 * protected resource and accessing the resource. Inserted for
164 		 * same reason as above.
165 		 */
166 		smp_mb();
167 
168 		if (type == TYPE_SWPB)
169 			swpbcounter++;
170 		else
171 			swpcounter++;
172 	}
173 
174 	return res;
175 }
176 
177 /*
178  * swp_handler logs the id of calling process, dissects the instruction, sanity
179  * checks the memory location, calls emulate_swpX for the actual operation and
180  * deals with fixup/error handling before returning
181  */
182 static int swp_handler(struct pt_regs *regs, unsigned int instr)
183 {
184 	unsigned int address, destreg, data, type;
185 	unsigned int res = 0;
186 
187 	perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
188 
189 	res = arm_check_condition(instr, regs->ARM_cpsr);
190 	switch (res) {
191 	case ARM_OPCODE_CONDTEST_PASS:
192 		break;
193 	case ARM_OPCODE_CONDTEST_FAIL:
194 		/* Condition failed - return to next instruction */
195 		regs->ARM_pc += 4;
196 		return 0;
197 	case ARM_OPCODE_CONDTEST_UNCOND:
198 		/* If unconditional encoding - not a SWP, undef */
199 		return -EFAULT;
200 	default:
201 		return -EINVAL;
202 	}
203 
204 	if (current->pid != previous_pid) {
205 		pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
206 			 current->comm, (unsigned long)current->pid);
207 		previous_pid = current->pid;
208 	}
209 
210 	address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
211 	data	= regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
212 	destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
213 
214 	type = instr & TYPE_SWPB;
215 
216 	pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
217 		 EXTRACT_REG_NUM(instr, RN_OFFSET), address,
218 		 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
219 
220 	/* Check access in reasonable access range for both SWP and SWPB */
221 	if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
222 		pr_debug("SWP{B} emulation: access to %p not allowed!\n",
223 			 (void *)address);
224 		res = -EFAULT;
225 	} else {
226 		res = emulate_swpX(address, &data, type);
227 	}
228 
229 	if (res == 0) {
230 		/*
231 		 * On successful emulation, revert the adjustment to the PC
232 		 * made in kernel/traps.c in order to resume execution at the
233 		 * instruction following the SWP{B}.
234 		 */
235 		regs->ARM_pc += 4;
236 		regs->uregs[destreg] = data;
237 	} else if (res == -EFAULT) {
238 		/*
239 		 * Memory errors do not mean emulation failed.
240 		 * Set up signal info to return SEGV, then return OK
241 		 */
242 		set_segfault(regs, address);
243 	}
244 
245 	return 0;
246 }
247 
248 /*
249  * Only emulate SWP/SWPB executed in ARM state/User mode.
250  * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
251  */
252 static struct undef_hook swp_hook = {
253 	.instr_mask = 0x0fb00ff0,
254 	.instr_val  = 0x01000090,
255 	.cpsr_mask  = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
256 	.cpsr_val   = USR_MODE,
257 	.fn	    = swp_handler
258 };
259 
260 /*
261  * Register handler and create status file in /proc/cpu
262  * Invoked as late_initcall, since not needed before init spawned.
263  */
264 static int __init swp_emulation_init(void)
265 {
266 #ifdef CONFIG_PROC_FS
267 	struct proc_dir_entry *res;
268 
269 	res = create_proc_entry("cpu/swp_emulation", S_IRUGO, NULL);
270 
271 	if (!res)
272 		return -ENOMEM;
273 
274 	res->read_proc = proc_read_status;
275 #endif /* CONFIG_PROC_FS */
276 
277 	printk(KERN_NOTICE "Registering SWP/SWPB emulation handler\n");
278 	register_undef_hook(&swp_hook);
279 
280 	return 0;
281 }
282 
283 late_initcall(swp_emulation_init);
284