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Leif Lindholm64d2dc32010-09-16 18:00:47 +01001/*
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>
David Howells526c5972013-04-11 03:05:01 +010024#include <linux/seq_file.h>
Leif Lindholm64d2dc32010-09-16 18:00:47 +010025#include <linux/sched.h>
Ingo Molnar589ee622017-02-04 00:16:44 +010026#include <linux/sched/mm.h>
Leif Lindholm64d2dc32010-09-16 18:00:47 +010027#include <linux/syscalls.h>
28#include <linux/perf_event.h>
29
Leif Lindholmc245dcd2011-12-12 19:45:24 +010030#include <asm/opcodes.h>
Russell King7397aa42014-07-04 14:49:05 +010031#include <asm/system_info.h>
Leif Lindholm64d2dc32010-09-16 18:00:47 +010032#include <asm/traps.h>
Linus Torvalds7c0f6ba2016-12-24 11:46:01 -080033#include <linux/uaccess.h>
Leif Lindholm64d2dc32010-09-16 18:00:47 +010034
35/*
36 * Error-checking SWP macros implemented using ldrex{b}/strex{b}
37 */
38#define __user_swpX_asm(data, addr, res, temp, B) \
39 __asm__ __volatile__( \
Shengjiu Wang34bfbae2015-12-08 13:37:19 +010040 "0: ldrex"B" %2, [%3]\n" \
41 "1: strex"B" %0, %1, [%3]\n" \
Leif Lindholm64d2dc32010-09-16 18:00:47 +010042 " cmp %0, #0\n" \
Shengjiu Wang34bfbae2015-12-08 13:37:19 +010043 " moveq %1, %2\n" \
Leif Lindholm64d2dc32010-09-16 18:00:47 +010044 " movne %0, %4\n" \
45 "2:\n" \
Ard Biesheuvelc4a84ae2015-03-24 10:41:09 +010046 " .section .text.fixup,\"ax\"\n" \
Leif Lindholm64d2dc32010-09-16 18:00:47 +010047 " .align 2\n" \
48 "3: mov %0, %5\n" \
49 " b 2b\n" \
50 " .previous\n" \
51 " .section __ex_table,\"a\"\n" \
52 " .align 3\n" \
53 " .long 0b, 3b\n" \
54 " .long 1b, 3b\n" \
55 " .previous" \
56 : "=&r" (res), "+r" (data), "=&r" (temp) \
57 : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \
58 : "cc", "memory")
59
60#define __user_swp_asm(data, addr, res, temp) \
61 __user_swpX_asm(data, addr, res, temp, "")
62#define __user_swpb_asm(data, addr, res, temp) \
63 __user_swpX_asm(data, addr, res, temp, "b")
64
65/*
66 * Macros/defines for extracting register numbers from instruction.
67 */
68#define EXTRACT_REG_NUM(instruction, offset) \
69 (((instruction) & (0xf << (offset))) >> (offset))
70#define RN_OFFSET 16
71#define RT_OFFSET 12
72#define RT2_OFFSET 0
73/*
74 * Bit 22 of the instruction encoding distinguishes between
75 * the SWP and SWPB variants (bit set means SWPB).
76 */
77#define TYPE_SWPB (1 << 22)
78
79static unsigned long swpcounter;
80static unsigned long swpbcounter;
81static unsigned long abtcounter;
82static pid_t previous_pid;
83
84#ifdef CONFIG_PROC_FS
David Howells526c5972013-04-11 03:05:01 +010085static int proc_status_show(struct seq_file *m, void *v)
Leif Lindholm64d2dc32010-09-16 18:00:47 +010086{
David Howells526c5972013-04-11 03:05:01 +010087 seq_printf(m, "Emulated SWP:\t\t%lu\n", swpcounter);
88 seq_printf(m, "Emulated SWPB:\t\t%lu\n", swpbcounter);
89 seq_printf(m, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
Leif Lindholm64d2dc32010-09-16 18:00:47 +010090 if (previous_pid != 0)
David Howells526c5972013-04-11 03:05:01 +010091 seq_printf(m, "Last process:\t\t%d\n", previous_pid);
92 return 0;
Leif Lindholm64d2dc32010-09-16 18:00:47 +010093}
94#endif
95
96/*
97 * Set up process info to signal segmentation fault - called on access error.
98 */
99static void set_segfault(struct pt_regs *regs, unsigned long addr)
100{
Eric W. Biederman05e792e2018-04-16 13:25:24 -0500101 int si_code;
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100102
Al Viro7bf9b7b2012-12-16 00:25:57 +0000103 down_read(&current->mm->mmap_sem);
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100104 if (find_vma(current->mm, addr) == NULL)
Eric W. Biederman05e792e2018-04-16 13:25:24 -0500105 si_code = SEGV_MAPERR;
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100106 else
Eric W. Biederman05e792e2018-04-16 13:25:24 -0500107 si_code = SEGV_ACCERR;
Al Viro7bf9b7b2012-12-16 00:25:57 +0000108 up_read(&current->mm->mmap_sem);
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100109
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100110 pr_debug("SWP{B} emulation: access caused memory abort!\n");
Eric W. Biederman05e792e2018-04-16 13:25:24 -0500111 arm_notify_die("Illegal memory access", regs,
112 SIGSEGV, si_code,
113 (void __user *)instruction_pointer(regs),
114 0, 0);
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100115
116 abtcounter++;
117}
118
119static int emulate_swpX(unsigned int address, unsigned int *data,
120 unsigned int type)
121{
122 unsigned int res = 0;
123
124 if ((type != TYPE_SWPB) && (address & 0x3)) {
125 /* SWP to unaligned address not permitted */
126 pr_debug("SWP instruction on unaligned pointer!\n");
127 return -EFAULT;
128 }
129
130 while (1) {
131 unsigned long temp;
Russell Kinga5e090a2015-08-19 20:40:41 +0100132 unsigned int __ua_flags;
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100133
Russell Kinga5e090a2015-08-19 20:40:41 +0100134 __ua_flags = uaccess_save_and_enable();
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100135 if (type == TYPE_SWPB)
136 __user_swpb_asm(*data, address, res, temp);
137 else
138 __user_swp_asm(*data, address, res, temp);
Russell Kinga5e090a2015-08-19 20:40:41 +0100139 uaccess_restore(__ua_flags);
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100140
141 if (likely(res != -EAGAIN) || signal_pending(current))
142 break;
143
144 cond_resched();
145 }
146
147 if (res == 0) {
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100148 if (type == TYPE_SWPB)
149 swpbcounter++;
150 else
151 swpcounter++;
152 }
153
154 return res;
155}
156
157/*
158 * swp_handler logs the id of calling process, dissects the instruction, sanity
159 * checks the memory location, calls emulate_swpX for the actual operation and
160 * deals with fixup/error handling before returning
161 */
162static int swp_handler(struct pt_regs *regs, unsigned int instr)
163{
164 unsigned int address, destreg, data, type;
165 unsigned int res = 0;
166
Peter Zijlstraa8b0ca12011-06-27 14:41:57 +0200167 perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100168
Leif Lindholmc245dcd2011-12-12 19:45:24 +0100169 res = arm_check_condition(instr, regs->ARM_cpsr);
170 switch (res) {
171 case ARM_OPCODE_CONDTEST_PASS:
172 break;
173 case ARM_OPCODE_CONDTEST_FAIL:
174 /* Condition failed - return to next instruction */
175 regs->ARM_pc += 4;
176 return 0;
177 case ARM_OPCODE_CONDTEST_UNCOND:
178 /* If unconditional encoding - not a SWP, undef */
179 return -EFAULT;
180 default:
181 return -EINVAL;
182 }
183
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100184 if (current->pid != previous_pid) {
185 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
186 current->comm, (unsigned long)current->pid);
187 previous_pid = current->pid;
188 }
189
190 address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
191 data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
192 destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
193
194 type = instr & TYPE_SWPB;
195
196 pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
197 EXTRACT_REG_NUM(instr, RN_OFFSET), address,
198 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
199
200 /* Check access in reasonable access range for both SWP and SWPB */
Linus Torvalds96d4f262019-01-03 18:57:57 -0800201 if (!access_ok((address & ~3), 4)) {
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100202 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
203 (void *)address);
204 res = -EFAULT;
205 } else {
206 res = emulate_swpX(address, &data, type);
207 }
208
209 if (res == 0) {
210 /*
211 * On successful emulation, revert the adjustment to the PC
212 * made in kernel/traps.c in order to resume execution at the
213 * instruction following the SWP{B}.
214 */
215 regs->ARM_pc += 4;
216 regs->uregs[destreg] = data;
217 } else if (res == -EFAULT) {
218 /*
219 * Memory errors do not mean emulation failed.
220 * Set up signal info to return SEGV, then return OK
221 */
222 set_segfault(regs, address);
223 }
224
225 return 0;
226}
227
228/*
229 * Only emulate SWP/SWPB executed in ARM state/User mode.
230 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
231 */
232static struct undef_hook swp_hook = {
233 .instr_mask = 0x0fb00ff0,
234 .instr_val = 0x01000090,
235 .cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
236 .cpsr_val = USR_MODE,
237 .fn = swp_handler
238};
239
240/*
241 * Register handler and create status file in /proc/cpu
242 * Invoked as late_initcall, since not needed before init spawned.
243 */
244static int __init swp_emulation_init(void)
245{
Russell King7397aa42014-07-04 14:49:05 +0100246 if (cpu_architecture() < CPU_ARCH_ARMv7)
247 return 0;
248
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100249#ifdef CONFIG_PROC_FS
Christoph Hellwig3f3942a2018-05-15 15:57:23 +0200250 if (!proc_create_single("cpu/swp_emulation", S_IRUGO, NULL,
251 proc_status_show))
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100252 return -ENOMEM;
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100253#endif /* CONFIG_PROC_FS */
254
Russell King4ed89f22014-10-28 11:26:42 +0000255 pr_notice("Registering SWP/SWPB emulation handler\n");
Leif Lindholm64d2dc32010-09-16 18:00:47 +0100256 register_undef_hook(&swp_hook);
257
258 return 0;
259}
260
261late_initcall(swp_emulation_init);