arch/arm/kernel/swp_emulate.c

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