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 down_read(¤t->mm->mmap_sem); 113 if (find_vma(current->mm, addr) == NULL) 114 info.si_code = SEGV_MAPERR; 115 else 116 info.si_code = SEGV_ACCERR; 117 up_read(¤t->mm->mmap_sem); 118 119 info.si_signo = SIGSEGV; 120 info.si_errno = 0; 121 info.si_addr = (void *) instruction_pointer(regs); 122 123 pr_debug("SWP{B} emulation: access caused memory abort!\n"); 124 arm_notify_die("Illegal memory access", regs, &info, 0, 0); 125 126 abtcounter++; 127 } 128 129 static int emulate_swpX(unsigned int address, unsigned int *data, 130 unsigned int type) 131 { 132 unsigned int res = 0; 133 134 if ((type != TYPE_SWPB) && (address & 0x3)) { 135 /* SWP to unaligned address not permitted */ 136 pr_debug("SWP instruction on unaligned pointer!\n"); 137 return -EFAULT; 138 } 139 140 while (1) { 141 unsigned long temp; 142 143 /* 144 * Barrier required between accessing protected resource and 145 * releasing a lock for it. Legacy code might not have done 146 * this, and we cannot determine that this is not the case 147 * being emulated, so insert always. 148 */ 149 smp_mb(); 150 151 if (type == TYPE_SWPB) 152 __user_swpb_asm(*data, address, res, temp); 153 else 154 __user_swp_asm(*data, address, res, temp); 155 156 if (likely(res != -EAGAIN) || signal_pending(current)) 157 break; 158 159 cond_resched(); 160 } 161 162 if (res == 0) { 163 /* 164 * Barrier also required between acquiring a lock for a 165 * protected resource and accessing the resource. Inserted for 166 * same reason as above. 167 */ 168 smp_mb(); 169 170 if (type == TYPE_SWPB) 171 swpbcounter++; 172 else 173 swpcounter++; 174 } 175 176 return res; 177 } 178 179 /* 180 * swp_handler logs the id of calling process, dissects the instruction, sanity 181 * checks the memory location, calls emulate_swpX for the actual operation and 182 * deals with fixup/error handling before returning 183 */ 184 static int swp_handler(struct pt_regs *regs, unsigned int instr) 185 { 186 unsigned int address, destreg, data, type; 187 unsigned int res = 0; 188 189 perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc); 190 191 res = arm_check_condition(instr, regs->ARM_cpsr); 192 switch (res) { 193 case ARM_OPCODE_CONDTEST_PASS: 194 break; 195 case ARM_OPCODE_CONDTEST_FAIL: 196 /* Condition failed - return to next instruction */ 197 regs->ARM_pc += 4; 198 return 0; 199 case ARM_OPCODE_CONDTEST_UNCOND: 200 /* If unconditional encoding - not a SWP, undef */ 201 return -EFAULT; 202 default: 203 return -EINVAL; 204 } 205 206 if (current->pid != previous_pid) { 207 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n", 208 current->comm, (unsigned long)current->pid); 209 previous_pid = current->pid; 210 } 211 212 address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)]; 213 data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)]; 214 destreg = EXTRACT_REG_NUM(instr, RT_OFFSET); 215 216 type = instr & TYPE_SWPB; 217 218 pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n", 219 EXTRACT_REG_NUM(instr, RN_OFFSET), address, 220 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data); 221 222 /* Check access in reasonable access range for both SWP and SWPB */ 223 if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) { 224 pr_debug("SWP{B} emulation: access to %p not allowed!\n", 225 (void *)address); 226 res = -EFAULT; 227 } else { 228 res = emulate_swpX(address, &data, type); 229 } 230 231 if (res == 0) { 232 /* 233 * On successful emulation, revert the adjustment to the PC 234 * made in kernel/traps.c in order to resume execution at the 235 * instruction following the SWP{B}. 236 */ 237 regs->ARM_pc += 4; 238 regs->uregs[destreg] = data; 239 } else if (res == -EFAULT) { 240 /* 241 * Memory errors do not mean emulation failed. 242 * Set up signal info to return SEGV, then return OK 243 */ 244 set_segfault(regs, address); 245 } 246 247 return 0; 248 } 249 250 /* 251 * Only emulate SWP/SWPB executed in ARM state/User mode. 252 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE. 253 */ 254 static struct undef_hook swp_hook = { 255 .instr_mask = 0x0fb00ff0, 256 .instr_val = 0x01000090, 257 .cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT, 258 .cpsr_val = USR_MODE, 259 .fn = swp_handler 260 }; 261 262 /* 263 * Register handler and create status file in /proc/cpu 264 * Invoked as late_initcall, since not needed before init spawned. 265 */ 266 static int __init swp_emulation_init(void) 267 { 268 #ifdef CONFIG_PROC_FS 269 struct proc_dir_entry *res; 270 271 res = create_proc_entry("cpu/swp_emulation", S_IRUGO, NULL); 272 273 if (!res) 274 return -ENOMEM; 275 276 res->read_proc = proc_read_status; 277 #endif /* CONFIG_PROC_FS */ 278 279 printk(KERN_NOTICE "Registering SWP/SWPB emulation handler\n"); 280 register_undef_hook(&swp_hook); 281 282 return 0; 283 } 284 285 late_initcall(swp_emulation_init); 286