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/seq_file.h> 25 #include <linux/sched.h> 26 #include <linux/sched/mm.h> 27 #include <linux/syscalls.h> 28 #include <linux/perf_event.h> 29 30 #include <asm/opcodes.h> 31 #include <asm/system_info.h> 32 #include <asm/traps.h> 33 #include <linux/uaccess.h> 34 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__( \ 40 "0: ldrex"B" %2, [%3]\n" \ 41 "1: strex"B" %0, %1, [%3]\n" \ 42 " cmp %0, #0\n" \ 43 " moveq %1, %2\n" \ 44 " movne %0, %4\n" \ 45 "2:\n" \ 46 " .section .text.fixup,\"ax\"\n" \ 47 " .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 79 static unsigned long swpcounter; 80 static unsigned long swpbcounter; 81 static unsigned long abtcounter; 82 static pid_t previous_pid; 83 84 #ifdef CONFIG_PROC_FS 85 static int proc_status_show(struct seq_file *m, void *v) 86 { 87 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); 90 if (previous_pid != 0) 91 seq_printf(m, "Last process:\t\t%d\n", previous_pid); 92 return 0; 93 } 94 95 static int proc_status_open(struct inode *inode, struct file *file) 96 { 97 return single_open(file, proc_status_show, PDE_DATA(inode)); 98 } 99 100 static const struct file_operations proc_status_fops = { 101 .open = proc_status_open, 102 .read = seq_read, 103 .llseek = seq_lseek, 104 .release = single_release, 105 }; 106 #endif 107 108 /* 109 * Set up process info to signal segmentation fault - called on access error. 110 */ 111 static void set_segfault(struct pt_regs *regs, unsigned long addr) 112 { 113 siginfo_t info; 114 115 down_read(¤t->mm->mmap_sem); 116 if (find_vma(current->mm, addr) == NULL) 117 info.si_code = SEGV_MAPERR; 118 else 119 info.si_code = SEGV_ACCERR; 120 up_read(¤t->mm->mmap_sem); 121 122 info.si_signo = SIGSEGV; 123 info.si_errno = 0; 124 info.si_addr = (void *) instruction_pointer(regs); 125 126 pr_debug("SWP{B} emulation: access caused memory abort!\n"); 127 arm_notify_die("Illegal memory access", regs, &info, 0, 0); 128 129 abtcounter++; 130 } 131 132 static int emulate_swpX(unsigned int address, unsigned int *data, 133 unsigned int type) 134 { 135 unsigned int res = 0; 136 137 if ((type != TYPE_SWPB) && (address & 0x3)) { 138 /* SWP to unaligned address not permitted */ 139 pr_debug("SWP instruction on unaligned pointer!\n"); 140 return -EFAULT; 141 } 142 143 while (1) { 144 unsigned long temp; 145 unsigned int __ua_flags; 146 147 __ua_flags = uaccess_save_and_enable(); 148 if (type == TYPE_SWPB) 149 __user_swpb_asm(*data, address, res, temp); 150 else 151 __user_swp_asm(*data, address, res, temp); 152 uaccess_restore(__ua_flags); 153 154 if (likely(res != -EAGAIN) || signal_pending(current)) 155 break; 156 157 cond_resched(); 158 } 159 160 if (res == 0) { 161 if (type == TYPE_SWPB) 162 swpbcounter++; 163 else 164 swpcounter++; 165 } 166 167 return res; 168 } 169 170 /* 171 * swp_handler logs the id of calling process, dissects the instruction, sanity 172 * checks the memory location, calls emulate_swpX for the actual operation and 173 * deals with fixup/error handling before returning 174 */ 175 static int swp_handler(struct pt_regs *regs, unsigned int instr) 176 { 177 unsigned int address, destreg, data, type; 178 unsigned int res = 0; 179 180 perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc); 181 182 res = arm_check_condition(instr, regs->ARM_cpsr); 183 switch (res) { 184 case ARM_OPCODE_CONDTEST_PASS: 185 break; 186 case ARM_OPCODE_CONDTEST_FAIL: 187 /* Condition failed - return to next instruction */ 188 regs->ARM_pc += 4; 189 return 0; 190 case ARM_OPCODE_CONDTEST_UNCOND: 191 /* If unconditional encoding - not a SWP, undef */ 192 return -EFAULT; 193 default: 194 return -EINVAL; 195 } 196 197 if (current->pid != previous_pid) { 198 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n", 199 current->comm, (unsigned long)current->pid); 200 previous_pid = current->pid; 201 } 202 203 address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)]; 204 data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)]; 205 destreg = EXTRACT_REG_NUM(instr, RT_OFFSET); 206 207 type = instr & TYPE_SWPB; 208 209 pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n", 210 EXTRACT_REG_NUM(instr, RN_OFFSET), address, 211 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data); 212 213 /* Check access in reasonable access range for both SWP and SWPB */ 214 if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) { 215 pr_debug("SWP{B} emulation: access to %p not allowed!\n", 216 (void *)address); 217 res = -EFAULT; 218 } else { 219 res = emulate_swpX(address, &data, type); 220 } 221 222 if (res == 0) { 223 /* 224 * On successful emulation, revert the adjustment to the PC 225 * made in kernel/traps.c in order to resume execution at the 226 * instruction following the SWP{B}. 227 */ 228 regs->ARM_pc += 4; 229 regs->uregs[destreg] = data; 230 } else if (res == -EFAULT) { 231 /* 232 * Memory errors do not mean emulation failed. 233 * Set up signal info to return SEGV, then return OK 234 */ 235 set_segfault(regs, address); 236 } 237 238 return 0; 239 } 240 241 /* 242 * Only emulate SWP/SWPB executed in ARM state/User mode. 243 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE. 244 */ 245 static struct undef_hook swp_hook = { 246 .instr_mask = 0x0fb00ff0, 247 .instr_val = 0x01000090, 248 .cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT, 249 .cpsr_val = USR_MODE, 250 .fn = swp_handler 251 }; 252 253 /* 254 * Register handler and create status file in /proc/cpu 255 * Invoked as late_initcall, since not needed before init spawned. 256 */ 257 static int __init swp_emulation_init(void) 258 { 259 if (cpu_architecture() < CPU_ARCH_ARMv7) 260 return 0; 261 262 #ifdef CONFIG_PROC_FS 263 if (!proc_create("cpu/swp_emulation", S_IRUGO, NULL, &proc_status_fops)) 264 return -ENOMEM; 265 #endif /* CONFIG_PROC_FS */ 266 267 pr_notice("Registering SWP/SWPB emulation handler\n"); 268 register_undef_hook(&swp_hook); 269 270 return 0; 271 } 272 273 late_initcall(swp_emulation_init); 274