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/opcodes.h>
  29 #include <asm/traps.h>
  30 #include <asm/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         "       mov             %2, %1\n"                       \
  38         "0:     ldrex"B"        %1, [%3]\n"                     \
  39         "1:     strex"B"        %0, %2, [%3]\n"                 \
  40         "       cmp             %0, #0\n"                       \
  41         "       movne           %0, %4\n"                       \
  42         "2:\n"                                                  \
  43         "       .section         .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_read_status(char *page, char **start, off_t off, int count,
  83                             int *eof, void *data)
  84 {
  85         char *p = page;
  86         int len;
  87
  88         p += sprintf(p, "Emulated SWP:\t\t%lu\n", swpcounter);
  89         p += sprintf(p, "Emulated SWPB:\t\t%lu\n", swpbcounter);
  90         p += sprintf(p, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
  91         if (previous_pid != 0)
  92                 p += sprintf(p, "Last process:\t\t%d\n", previous_pid);
  93
  94         len = (p - page) - off;
  95         if (len < 0)
  96                 len = 0;
  97
  98         *eof = (len <= count) ? 1 : 0;
  99         *start = page + off;
 100
 101         return len;
 102 }
 103 #endif
 104
 105 /*
 106  * Set up process info to signal segmentation fault - called on access error.
 107  */
 108 static void set_segfault(struct pt_regs *regs, unsigned long addr)
 109 {
 110         siginfo_t info;
 111
 112         if (find_vma(current->mm, addr) == NULL)
 113                 info.si_code = SEGV_MAPERR;
 114         else
 115                 info.si_code = SEGV_ACCERR;
 116
 117         info.si_signo = SIGSEGV;
 118         info.si_errno = 0;
 119         info.si_addr  = (void *) instruction_pointer(regs);
 120
 121         pr_debug("SWP{B} emulation: access caused memory abort!\n");
 122         arm_notify_die("Illegal memory access", regs, &info, 0, 0);
 123
 124         abtcounter++;
 125 }
 126
 127 static int emulate_swpX(unsigned int address, unsigned int *data,
 128                         unsigned int type)
 129 {
 130         unsigned int res = 0;
 131
 132         if ((type != TYPE_SWPB) && (address & 0x3)) {
 133                 /* SWP to unaligned address not permitted */
 134                 pr_debug("SWP instruction on unaligned pointer!\n");
 135                 return -EFAULT;
 136         }
 137
 138         while (1) {
 139                 unsigned long temp;
 140
 141                 /*
 142                  * Barrier required between accessing protected resource and
 143                  * releasing a lock for it. Legacy code might not have done
 144                  * this, and we cannot determine that this is not the case
 145                  * being emulated, so insert always.
 146                  */
 147                 smp_mb();
 148
 149                 if (type == TYPE_SWPB)
 150                         __user_swpb_asm(*data, address, res, temp);
 151                 else
 152                         __user_swp_asm(*data, address, res, temp);
 153
 154                 if (likely(res != -EAGAIN) || signal_pending(current))
 155                         break;
 156
 157                 cond_resched();
 158         }
 159
 160         if (res == 0) {
 161                 /*
 162                  * Barrier also required between acquiring a lock for a
 163                  * protected resource and accessing the resource. Inserted for
 164                  * same reason as above.
 165                  */
 166                 smp_mb();
 167
 168                 if (type == TYPE_SWPB)
 169                         swpbcounter++;
 170                 else
 171                         swpcounter++;
 172         }
 173
 174         return res;
 175 }
 176
 177 /*
 178  * swp_handler logs the id of calling process, dissects the instruction, sanity
 179  * checks the memory location, calls emulate_swpX for the actual operation and
 180  * deals with fixup/error handling before returning
 181  */
 182 static int swp_handler(struct pt_regs *regs, unsigned int instr)
 183 {
 184         unsigned int address, destreg, data, type;
 185         unsigned int res = 0;
 186
 187         perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
 188
 189         res = arm_check_condition(instr, regs->ARM_cpsr);
 190         switch (res) {
 191         case ARM_OPCODE_CONDTEST_PASS:
 192                 break;
 193         case ARM_OPCODE_CONDTEST_FAIL:
 194                 /* Condition failed - return to next instruction */
 195                 regs->ARM_pc += 4;
 196                 return 0;
 197         case ARM_OPCODE_CONDTEST_UNCOND:
 198                 /* If unconditional encoding - not a SWP, undef */
 199                 return -EFAULT;
 200         default:
 201                 return -EINVAL;
 202         }
 203
 204         if (current->pid != previous_pid) {
 205                 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
 206                          current->comm, (unsigned long)current->pid);
 207                 previous_pid = current->pid;
 208         }
 209
 210         address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
 211         data    = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
 212         destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
 213
 214         type = instr & TYPE_SWPB;
 215
 216         pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
 217                  EXTRACT_REG_NUM(instr, RN_OFFSET), address,
 218                  destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
 219
 220         /* Check access in reasonable access range for both SWP and SWPB */
 221         if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
 222                 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
 223                          (void *)address);
 224                 res = -EFAULT;
 225         } else {
 226                 res = emulate_swpX(address, &data, type);
 227         }
 228
 229         if (res == 0) {
 230                 /*
 231                  * On successful emulation, revert the adjustment to the PC
 232                  * made in kernel/traps.c in order to resume execution at the
 233                  * instruction following the SWP{B}.
 234                  */
 235                 regs->ARM_pc += 4;
 236                 regs->uregs[destreg] = data;
 237         } else if (res == -EFAULT) {
 238                 /*
 239                  * Memory errors do not mean emulation failed.
 240                  * Set up signal info to return SEGV, then return OK
 241                  */
 242                 set_segfault(regs, address);
 243         }
 244
 245         return 0;
 246 }
 247
 248 /*
 249  * Only emulate SWP/SWPB executed in ARM state/User mode.
 250  * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
 251  */
 252 static struct undef_hook swp_hook = {
 253         .instr_mask = 0x0fb00ff0,
 254         .instr_val  = 0x01000090,
 255         .cpsr_mask  = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
 256         .cpsr_val   = USR_MODE,
 257         .fn         = swp_handler
 258 };
 259
 260 /*
 261  * Register handler and create status file in /proc/cpu
 262  * Invoked as late_initcall, since not needed before init spawned.
 263  */
 264 static int __init swp_emulation_init(void)
 265 {
 266 #ifdef CONFIG_PROC_FS
 267         struct proc_dir_entry *res;
 268
 269         res = create_proc_entry("cpu/swp_emulation", S_IRUGO, NULL);
 270
 271         if (!res)
 272                 return -ENOMEM;
 273
 274         res->read_proc = proc_read_status;
 275 #endif /* CONFIG_PROC_FS */
 276
 277         printk(KERN_NOTICE "Registering SWP/SWPB emulation handler\n");
 278         register_undef_hook(&swp_hook);
 279
 280         return 0;
 281 }
 282
 283 late_initcall(swp_emulation_init);