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/traps.h> 29 #include <asm/uaccess.h> 30 31 /* 32 * Error-checking SWP macros implemented using ldrex{b}/strex{b} 33 */ 34 #define __user_swpX_asm(data, addr, res, temp, B) \ 35 __asm__ __volatile__( \ 36 " mov %2, %1\n" \ 37 "0: ldrex"B" %1, [%3]\n" \ 38 "1: strex"B" %0, %2, [%3]\n" \ 39 " cmp %0, #0\n" \ 40 " movne %0, %4\n" \ 41 "2:\n" \ 42 " .section .fixup,\"ax\"\n" \ 43 " .align 2\n" \ 44 "3: mov %0, %5\n" \ 45 " b 2b\n" \ 46 " .previous\n" \ 47 " .section __ex_table,\"a\"\n" \ 48 " .align 3\n" \ 49 " .long 0b, 3b\n" \ 50 " .long 1b, 3b\n" \ 51 " .previous" \ 52 : "=&r" (res), "+r" (data), "=&r" (temp) \ 53 : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \ 54 : "cc", "memory") 55 56 #define __user_swp_asm(data, addr, res, temp) \ 57 __user_swpX_asm(data, addr, res, temp, "") 58 #define __user_swpb_asm(data, addr, res, temp) \ 59 __user_swpX_asm(data, addr, res, temp, "b") 60 61 /* 62 * Macros/defines for extracting register numbers from instruction. 63 */ 64 #define EXTRACT_REG_NUM(instruction, offset) \ 65 (((instruction) & (0xf << (offset))) >> (offset)) 66 #define RN_OFFSET 16 67 #define RT_OFFSET 12 68 #define RT2_OFFSET 0 69 /* 70 * Bit 22 of the instruction encoding distinguishes between 71 * the SWP and SWPB variants (bit set means SWPB). 72 */ 73 #define TYPE_SWPB (1 << 22) 74 75 static unsigned long swpcounter; 76 static unsigned long swpbcounter; 77 static unsigned long abtcounter; 78 static pid_t previous_pid; 79 80 #ifdef CONFIG_PROC_FS 81 static int proc_read_status(char *page, char **start, off_t off, int count, 82 int *eof, void *data) 83 { 84 char *p = page; 85 int len; 86 87 p += sprintf(p, "Emulated SWP:\t\t%lu\n", swpcounter); 88 p += sprintf(p, "Emulated SWPB:\t\t%lu\n", swpbcounter); 89 p += sprintf(p, "Aborted SWP{B}:\t\t%lu\n", abtcounter); 90 if (previous_pid != 0) 91 p += sprintf(p, "Last process:\t\t%d\n", previous_pid); 92 93 len = (p - page) - off; 94 if (len < 0) 95 len = 0; 96 97 *eof = (len <= count) ? 1 : 0; 98 *start = page + off; 99 100 return len; 101 } 102 #endif 103 104 /* 105 * Set up process info to signal segmentation fault - called on access error. 106 */ 107 static void set_segfault(struct pt_regs *regs, unsigned long addr) 108 { 109 siginfo_t info; 110 111 if (find_vma(current->mm, addr) == NULL) 112 info.si_code = SEGV_MAPERR; 113 else 114 info.si_code = SEGV_ACCERR; 115 116 info.si_signo = SIGSEGV; 117 info.si_errno = 0; 118 info.si_addr = (void *) instruction_pointer(regs); 119 120 pr_debug("SWP{B} emulation: access caused memory abort!\n"); 121 arm_notify_die("Illegal memory access", regs, &info, 0, 0); 122 123 abtcounter++; 124 } 125 126 static int emulate_swpX(unsigned int address, unsigned int *data, 127 unsigned int type) 128 { 129 unsigned int res = 0; 130 131 if ((type != TYPE_SWPB) && (address & 0x3)) { 132 /* SWP to unaligned address not permitted */ 133 pr_debug("SWP instruction on unaligned pointer!\n"); 134 return -EFAULT; 135 } 136 137 while (1) { 138 unsigned long temp; 139 140 /* 141 * Barrier required between accessing protected resource and 142 * releasing a lock for it. Legacy code might not have done 143 * this, and we cannot determine that this is not the case 144 * being emulated, so insert always. 145 */ 146 smp_mb(); 147 148 if (type == TYPE_SWPB) 149 __user_swpb_asm(*data, address, res, temp); 150 else 151 __user_swp_asm(*data, address, res, temp); 152 153 if (likely(res != -EAGAIN) || signal_pending(current)) 154 break; 155 156 cond_resched(); 157 } 158 159 if (res == 0) { 160 /* 161 * Barrier also required between aquiring a lock for a 162 * protected resource and accessing the resource. Inserted for 163 * same reason as above. 164 */ 165 smp_mb(); 166 167 if (type == TYPE_SWPB) 168 swpbcounter++; 169 else 170 swpcounter++; 171 } 172 173 return res; 174 } 175 176 /* 177 * swp_handler logs the id of calling process, dissects the instruction, sanity 178 * checks the memory location, calls emulate_swpX for the actual operation and 179 * deals with fixup/error handling before returning 180 */ 181 static int swp_handler(struct pt_regs *regs, unsigned int instr) 182 { 183 unsigned int address, destreg, data, type; 184 unsigned int res = 0; 185 186 perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, 0, regs, regs->ARM_pc); 187 188 if (current->pid != previous_pid) { 189 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n", 190 current->comm, (unsigned long)current->pid); 191 previous_pid = current->pid; 192 } 193 194 address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)]; 195 data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)]; 196 destreg = EXTRACT_REG_NUM(instr, RT_OFFSET); 197 198 type = instr & TYPE_SWPB; 199 200 pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n", 201 EXTRACT_REG_NUM(instr, RN_OFFSET), address, 202 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data); 203 204 /* Check access in reasonable access range for both SWP and SWPB */ 205 if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) { 206 pr_debug("SWP{B} emulation: access to %p not allowed!\n", 207 (void *)address); 208 res = -EFAULT; 209 } else { 210 res = emulate_swpX(address, &data, type); 211 } 212 213 if (res == 0) { 214 /* 215 * On successful emulation, revert the adjustment to the PC 216 * made in kernel/traps.c in order to resume execution at the 217 * instruction following the SWP{B}. 218 */ 219 regs->ARM_pc += 4; 220 regs->uregs[destreg] = data; 221 } else if (res == -EFAULT) { 222 /* 223 * Memory errors do not mean emulation failed. 224 * Set up signal info to return SEGV, then return OK 225 */ 226 set_segfault(regs, address); 227 } 228 229 return 0; 230 } 231 232 /* 233 * Only emulate SWP/SWPB executed in ARM state/User mode. 234 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE. 235 */ 236 static struct undef_hook swp_hook = { 237 .instr_mask = 0x0fb00ff0, 238 .instr_val = 0x01000090, 239 .cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT, 240 .cpsr_val = USR_MODE, 241 .fn = swp_handler 242 }; 243 244 /* 245 * Register handler and create status file in /proc/cpu 246 * Invoked as late_initcall, since not needed before init spawned. 247 */ 248 static int __init swp_emulation_init(void) 249 { 250 #ifdef CONFIG_PROC_FS 251 struct proc_dir_entry *res; 252 253 res = create_proc_entry("cpu/swp_emulation", S_IRUGO, NULL); 254 255 if (!res) 256 return -ENOMEM; 257 258 res->read_proc = proc_read_status; 259 #endif /* CONFIG_PROC_FS */ 260 261 printk(KERN_NOTICE "Registering SWP/SWPB emulation handler\n"); 262 register_undef_hook(&swp_hook); 263 264 return 0; 265 } 266 267 late_initcall(swp_emulation_init); 268