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         down_read(&current->mm->mmap_sem);
 113         if (find_vma(current->mm, addr) == NULL)
 114                 info.si_code = SEGV_MAPERR;
 115         else
 116                 info.si_code = SEGV_ACCERR;
 117         up_read(&current->mm->mmap_sem);
 118
 119         info.si_signo = SIGSEGV;
 120         info.si_errno = 0;
 121         info.si_addr  = (void *) instruction_pointer(regs);
 122
 123         pr_debug("SWP{B} emulation: access caused memory abort!\n");
 124         arm_notify_die("Illegal memory access", regs, &info, 0, 0);
 125
 126         abtcounter++;
 127 }
 128
 129 static int emulate_swpX(unsigned int address, unsigned int *data,
 130                         unsigned int type)
 131 {
 132         unsigned int res = 0;
 133
 134         if ((type != TYPE_SWPB) && (address & 0x3)) {
 135                 /* SWP to unaligned address not permitted */
 136                 pr_debug("SWP instruction on unaligned pointer!\n");
 137                 return -EFAULT;
 138         }
 139
 140         while (1) {
 141                 unsigned long temp;
 142
 143                 /*
 144                  * Barrier required between accessing protected resource and
 145                  * releasing a lock for it. Legacy code might not have done
 146                  * this, and we cannot determine that this is not the case
 147                  * being emulated, so insert always.
 148                  */
 149                 smp_mb();
 150
 151                 if (type == TYPE_SWPB)
 152                         __user_swpb_asm(*data, address, res, temp);
 153                 else
 154                         __user_swp_asm(*data, address, res, temp);
 155
 156                 if (likely(res != -EAGAIN) || signal_pending(current))
 157                         break;
 158
 159                 cond_resched();
 160         }
 161
 162         if (res == 0) {
 163                 /*
 164                  * Barrier also required between acquiring a lock for a
 165                  * protected resource and accessing the resource. Inserted for
 166                  * same reason as above.
 167                  */
 168                 smp_mb();
 169
 170                 if (type == TYPE_SWPB)
 171                         swpbcounter++;
 172                 else
 173                         swpcounter++;
 174         }
 175
 176         return res;
 177 }
 178
 179 /*
 180  * swp_handler logs the id of calling process, dissects the instruction, sanity
 181  * checks the memory location, calls emulate_swpX for the actual operation and
 182  * deals with fixup/error handling before returning
 183  */
 184 static int swp_handler(struct pt_regs *regs, unsigned int instr)
 185 {
 186         unsigned int address, destreg, data, type;
 187         unsigned int res = 0;
 188
 189         perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
 190
 191         res = arm_check_condition(instr, regs->ARM_cpsr);
 192         switch (res) {
 193         case ARM_OPCODE_CONDTEST_PASS:
 194                 break;
 195         case ARM_OPCODE_CONDTEST_FAIL:
 196                 /* Condition failed - return to next instruction */
 197                 regs->ARM_pc += 4;
 198                 return 0;
 199         case ARM_OPCODE_CONDTEST_UNCOND:
 200                 /* If unconditional encoding - not a SWP, undef */
 201                 return -EFAULT;
 202         default:
 203                 return -EINVAL;
 204         }
 205
 206         if (current->pid != previous_pid) {
 207                 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
 208                          current->comm, (unsigned long)current->pid);
 209                 previous_pid = current->pid;
 210         }
 211
 212         address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
 213         data    = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
 214         destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
 215
 216         type = instr & TYPE_SWPB;
 217
 218         pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
 219                  EXTRACT_REG_NUM(instr, RN_OFFSET), address,
 220                  destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
 221
 222         /* Check access in reasonable access range for both SWP and SWPB */
 223         if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
 224                 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
 225                          (void *)address);
 226                 res = -EFAULT;
 227         } else {
 228                 res = emulate_swpX(address, &data, type);
 229         }
 230
 231         if (res == 0) {
 232                 /*
 233                  * On successful emulation, revert the adjustment to the PC
 234                  * made in kernel/traps.c in order to resume execution at the
 235                  * instruction following the SWP{B}.
 236                  */
 237                 regs->ARM_pc += 4;
 238                 regs->uregs[destreg] = data;
 239         } else if (res == -EFAULT) {
 240                 /*
 241                  * Memory errors do not mean emulation failed.
 242                  * Set up signal info to return SEGV, then return OK
 243                  */
 244                 set_segfault(regs, address);
 245         }
 246
 247         return 0;
 248 }
 249
 250 /*
 251  * Only emulate SWP/SWPB executed in ARM state/User mode.
 252  * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
 253  */
 254 static struct undef_hook swp_hook = {
 255         .instr_mask = 0x0fb00ff0,
 256         .instr_val  = 0x01000090,
 257         .cpsr_mask  = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
 258         .cpsr_val   = USR_MODE,
 259         .fn         = swp_handler
 260 };
 261
 262 /*
 263  * Register handler and create status file in /proc/cpu
 264  * Invoked as late_initcall, since not needed before init spawned.
 265  */
 266 static int __init swp_emulation_init(void)
 267 {
 268 #ifdef CONFIG_PROC_FS
 269         struct proc_dir_entry *res;
 270
 271         res = create_proc_entry("cpu/swp_emulation", S_IRUGO, NULL);
 272
 273         if (!res)
 274                 return -ENOMEM;
 275
 276         res->read_proc = proc_read_status;
 277 #endif /* CONFIG_PROC_FS */
 278
 279         printk(KERN_NOTICE "Registering SWP/SWPB emulation handler\n");
 280         register_undef_hook(&swp_hook);
 281
 282         return 0;
 283 }
 284
 285 late_initcall(swp_emulation_init);