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 ".arch armv7-a\n" \ 38 "0: ldrex"B" %2, [%3]\n" \ 39 "1: strex"B" %0, %1, [%3]\n" \ 40 " cmp %0, #0\n" \ 41 " moveq %1, %2\n" \ 42 " movne %0, %4\n" \ 43 "2:\n" \ 44 " .section .text.fixup,\"ax\"\n" \ 45 " .align 2\n" \ 46 "3: mov %0, %5\n" \ 47 " b 2b\n" \ 48 " .previous\n" \ 49 " .section __ex_table,\"a\"\n" \ 50 " .align 3\n" \ 51 " .long 0b, 3b\n" \ 52 " .long 1b, 3b\n" \ 53 " .previous" \ 54 : "=&r" (res), "+r" (data), "=&r" (temp) \ 55 : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \ 56 : "cc", "memory") 57 58#define __user_swp_asm(data, addr, res, temp) \ 59 __user_swpX_asm(data, addr, res, temp, "") 60#define __user_swpb_asm(data, addr, res, temp) \ 61 __user_swpX_asm(data, addr, res, temp, "b") 62 63/* 64 * Macros/defines for extracting register numbers from instruction. 65 */ 66#define EXTRACT_REG_NUM(instruction, offset) \ 67 (((instruction) & (0xf << (offset))) >> (offset)) 68#define RN_OFFSET 16 69#define RT_OFFSET 12 70#define RT2_OFFSET 0 71/* 72 * Bit 22 of the instruction encoding distinguishes between 73 * the SWP and SWPB variants (bit set means SWPB). 74 */ 75#define TYPE_SWPB (1 << 22) 76 77static unsigned long swpcounter; 78static unsigned long swpbcounter; 79static unsigned long abtcounter; 80static pid_t previous_pid; 81 82#ifdef CONFIG_PROC_FS 83static int proc_status_show(struct seq_file *m, void *v) 84{ 85 seq_printf(m, "Emulated SWP:\t\t%lu\n", swpcounter); 86 seq_printf(m, "Emulated SWPB:\t\t%lu\n", swpbcounter); 87 seq_printf(m, "Aborted SWP{B}:\t\t%lu\n", abtcounter); 88 if (previous_pid != 0) 89 seq_printf(m, "Last process:\t\t%d\n", previous_pid); 90 return 0; 91} 92#endif 93 94/* 95 * Set up process info to signal segmentation fault - called on access error. 96 */ 97static void set_segfault(struct pt_regs *regs, unsigned long addr) 98{ 99 int si_code; 100 101 mmap_read_lock(current->mm); 102 if (find_vma(current->mm, addr) == NULL) 103 si_code = SEGV_MAPERR; 104 else 105 si_code = SEGV_ACCERR; 106 mmap_read_unlock(current->mm); 107 108 pr_debug("SWP{B} emulation: access caused memory abort!\n"); 109 arm_notify_die("Illegal memory access", regs, 110 SIGSEGV, si_code, 111 (void __user *)instruction_pointer(regs), 112 0, 0); 113 114 abtcounter++; 115} 116 117static int emulate_swpX(unsigned int address, unsigned int *data, 118 unsigned int type) 119{ 120 unsigned int res = 0; 121 122 if ((type != TYPE_SWPB) && (address & 0x3)) { 123 /* SWP to unaligned address not permitted */ 124 pr_debug("SWP instruction on unaligned pointer!\n"); 125 return -EFAULT; 126 } 127 128 while (1) { 129 unsigned long temp; 130 unsigned int __ua_flags; 131 132 __ua_flags = uaccess_save_and_enable(); 133 if (type == TYPE_SWPB) 134 __user_swpb_asm(*data, address, res, temp); 135 else 136 __user_swp_asm(*data, address, res, temp); 137 uaccess_restore(__ua_flags); 138 139 if (likely(res != -EAGAIN) || signal_pending(current)) 140 break; 141 142 cond_resched(); 143 } 144 145 if (res == 0) { 146 if (type == TYPE_SWPB) 147 swpbcounter++; 148 else 149 swpcounter++; 150 } 151 152 return res; 153} 154 155/* 156 * swp_handler logs the id of calling process, dissects the instruction, sanity 157 * checks the memory location, calls emulate_swpX for the actual operation and 158 * deals with fixup/error handling before returning 159 */ 160static int swp_handler(struct pt_regs *regs, unsigned int instr) 161{ 162 unsigned int address, destreg, data, type; 163 unsigned int res = 0; 164 165 perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc); 166 167 res = arm_check_condition(instr, regs->ARM_cpsr); 168 switch (res) { 169 case ARM_OPCODE_CONDTEST_PASS: 170 break; 171 case ARM_OPCODE_CONDTEST_FAIL: 172 /* Condition failed - return to next instruction */ 173 regs->ARM_pc += 4; 174 return 0; 175 case ARM_OPCODE_CONDTEST_UNCOND: 176 /* If unconditional encoding - not a SWP, undef */ 177 return -EFAULT; 178 default: 179 return -EINVAL; 180 } 181 182 if (current->pid != previous_pid) { 183 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n", 184 current->comm, (unsigned long)current->pid); 185 previous_pid = current->pid; 186 } 187 188 address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)]; 189 data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)]; 190 destreg = EXTRACT_REG_NUM(instr, RT_OFFSET); 191 192 type = instr & TYPE_SWPB; 193 194 pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n", 195 EXTRACT_REG_NUM(instr, RN_OFFSET), address, 196 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data); 197 198 /* Check access in reasonable access range for both SWP and SWPB */ 199 if (!access_ok((void __user *)(address & ~3), 4)) { 200 pr_debug("SWP{B} emulation: access to %p not allowed!\n", 201 (void *)address); 202 res = -EFAULT; 203 } else { 204 res = emulate_swpX(address, &data, type); 205 } 206 207 if (res == 0) { 208 /* 209 * On successful emulation, revert the adjustment to the PC 210 * made in kernel/traps.c in order to resume execution at the 211 * instruction following the SWP{B}. 212 */ 213 regs->ARM_pc += 4; 214 regs->uregs[destreg] = data; 215 } else if (res == -EFAULT) { 216 /* 217 * Memory errors do not mean emulation failed. 218 * Set up signal info to return SEGV, then return OK 219 */ 220 set_segfault(regs, address); 221 } 222 223 return 0; 224} 225 226/* 227 * Only emulate SWP/SWPB executed in ARM state/User mode. 228 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE. 229 */ 230static struct undef_hook swp_hook = { 231 .instr_mask = 0x0fb00ff0, 232 .instr_val = 0x01000090, 233 .cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT, 234 .cpsr_val = USR_MODE, 235 .fn = swp_handler 236}; 237 238/* 239 * Register handler and create status file in /proc/cpu 240 * Invoked as late_initcall, since not needed before init spawned. 241 */ 242static int __init swp_emulation_init(void) 243{ 244 if (cpu_architecture() < CPU_ARCH_ARMv7) 245 return 0; 246 247#ifdef CONFIG_PROC_FS 248 if (!proc_create_single("cpu/swp_emulation", S_IRUGO, NULL, 249 proc_status_show)) 250 return -ENOMEM; 251#endif /* CONFIG_PROC_FS */ 252 253 pr_notice("Registering SWP/SWPB emulation handler\n"); 254 register_undef_hook(&swp_hook); 255 256 return 0; 257} 258 259late_initcall(swp_emulation_init); 260