1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * linux/arch/arm/kernel/swp_emulate.c 4 * 5 * Copyright (C) 2009 ARM Limited 6 * __user_* functions adapted from include/asm/uaccess.h 7 * 8 * Implements emulation of the SWP/SWPB instructions using load-exclusive and 9 * store-exclusive for processors that have them disabled (or future ones that 10 * might not implement them). 11 * 12 * Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>] 13 * Where: Rt = destination 14 * Rt2 = source 15 * Rn = address 16 */ 17 18 #include <linux/init.h> 19 #include <linux/kernel.h> 20 #include <linux/proc_fs.h> 21 #include <linux/seq_file.h> 22 #include <linux/sched.h> 23 #include <linux/sched/mm.h> 24 #include <linux/syscalls.h> 25 #include <linux/perf_event.h> 26 27 #include <asm/opcodes.h> 28 #include <asm/system_info.h> 29 #include <asm/traps.h> 30 #include <linux/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 "0: ldrex"B" %2, [%3]\n" \ 38 "1: strex"B" %0, %1, [%3]\n" \ 39 " cmp %0, #0\n" \ 40 " moveq %1, %2\n" \ 41 " movne %0, %4\n" \ 42 "2:\n" \ 43 " .section .text.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_status_show(struct seq_file *m, void *v) 83 { 84 seq_printf(m, "Emulated SWP:\t\t%lu\n", swpcounter); 85 seq_printf(m, "Emulated SWPB:\t\t%lu\n", swpbcounter); 86 seq_printf(m, "Aborted SWP{B}:\t\t%lu\n", abtcounter); 87 if (previous_pid != 0) 88 seq_printf(m, "Last process:\t\t%d\n", previous_pid); 89 return 0; 90 } 91 #endif 92 93 /* 94 * Set up process info to signal segmentation fault - called on access error. 95 */ 96 static void set_segfault(struct pt_regs *regs, unsigned long addr) 97 { 98 int si_code; 99 100 mmap_read_lock(current->mm); 101 if (find_vma(current->mm, addr) == NULL) 102 si_code = SEGV_MAPERR; 103 else 104 si_code = SEGV_ACCERR; 105 mmap_read_unlock(current->mm); 106 107 pr_debug("SWP{B} emulation: access caused memory abort!\n"); 108 arm_notify_die("Illegal memory access", regs, 109 SIGSEGV, si_code, 110 (void __user *)instruction_pointer(regs), 111 0, 0); 112 113 abtcounter++; 114 } 115 116 static int emulate_swpX(unsigned int address, unsigned int *data, 117 unsigned int type) 118 { 119 unsigned int res = 0; 120 121 if ((type != TYPE_SWPB) && (address & 0x3)) { 122 /* SWP to unaligned address not permitted */ 123 pr_debug("SWP instruction on unaligned pointer!\n"); 124 return -EFAULT; 125 } 126 127 while (1) { 128 unsigned long temp; 129 unsigned int __ua_flags; 130 131 __ua_flags = uaccess_save_and_enable(); 132 if (type == TYPE_SWPB) 133 __user_swpb_asm(*data, address, res, temp); 134 else 135 __user_swp_asm(*data, address, res, temp); 136 uaccess_restore(__ua_flags); 137 138 if (likely(res != -EAGAIN) || signal_pending(current)) 139 break; 140 141 cond_resched(); 142 } 143 144 if (res == 0) { 145 if (type == TYPE_SWPB) 146 swpbcounter++; 147 else 148 swpcounter++; 149 } 150 151 return res; 152 } 153 154 /* 155 * swp_handler logs the id of calling process, dissects the instruction, sanity 156 * checks the memory location, calls emulate_swpX for the actual operation and 157 * deals with fixup/error handling before returning 158 */ 159 static int swp_handler(struct pt_regs *regs, unsigned int instr) 160 { 161 unsigned int address, destreg, data, type; 162 unsigned int res = 0; 163 164 perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc); 165 166 res = arm_check_condition(instr, regs->ARM_cpsr); 167 switch (res) { 168 case ARM_OPCODE_CONDTEST_PASS: 169 break; 170 case ARM_OPCODE_CONDTEST_FAIL: 171 /* Condition failed - return to next instruction */ 172 regs->ARM_pc += 4; 173 return 0; 174 case ARM_OPCODE_CONDTEST_UNCOND: 175 /* If unconditional encoding - not a SWP, undef */ 176 return -EFAULT; 177 default: 178 return -EINVAL; 179 } 180 181 if (current->pid != previous_pid) { 182 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n", 183 current->comm, (unsigned long)current->pid); 184 previous_pid = current->pid; 185 } 186 187 address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)]; 188 data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)]; 189 destreg = EXTRACT_REG_NUM(instr, RT_OFFSET); 190 191 type = instr & TYPE_SWPB; 192 193 pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n", 194 EXTRACT_REG_NUM(instr, RN_OFFSET), address, 195 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data); 196 197 /* Check access in reasonable access range for both SWP and SWPB */ 198 if (!access_ok((address & ~3), 4)) { 199 pr_debug("SWP{B} emulation: access to %p not allowed!\n", 200 (void *)address); 201 res = -EFAULT; 202 } else { 203 res = emulate_swpX(address, &data, type); 204 } 205 206 if (res == 0) { 207 /* 208 * On successful emulation, revert the adjustment to the PC 209 * made in kernel/traps.c in order to resume execution at the 210 * instruction following the SWP{B}. 211 */ 212 regs->ARM_pc += 4; 213 regs->uregs[destreg] = data; 214 } else if (res == -EFAULT) { 215 /* 216 * Memory errors do not mean emulation failed. 217 * Set up signal info to return SEGV, then return OK 218 */ 219 set_segfault(regs, address); 220 } 221 222 return 0; 223 } 224 225 /* 226 * Only emulate SWP/SWPB executed in ARM state/User mode. 227 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE. 228 */ 229 static struct undef_hook swp_hook = { 230 .instr_mask = 0x0fb00ff0, 231 .instr_val = 0x01000090, 232 .cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT, 233 .cpsr_val = USR_MODE, 234 .fn = swp_handler 235 }; 236 237 /* 238 * Register handler and create status file in /proc/cpu 239 * Invoked as late_initcall, since not needed before init spawned. 240 */ 241 static int __init swp_emulation_init(void) 242 { 243 if (cpu_architecture() < CPU_ARCH_ARMv7) 244 return 0; 245 246 #ifdef CONFIG_PROC_FS 247 if (!proc_create_single("cpu/swp_emulation", S_IRUGO, NULL, 248 proc_status_show)) 249 return -ENOMEM; 250 #endif /* CONFIG_PROC_FS */ 251 252 pr_notice("Registering SWP/SWPB emulation handler\n"); 253 register_undef_hook(&swp_hook); 254 255 return 0; 256 } 257 258 late_initcall(swp_emulation_init); 259