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/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 acquiring 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, 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);