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/syscalls.h>
  27 #include <linux/perf_event.h>
  28
  29 #include <asm/opcodes.h>
  30 #include <asm/traps.h>
  31 #include <asm/uaccess.h>
  32
  33 /*
  34  * Error-checking SWP macros implemented using ldrex{b}/strex{b}
  35  */
  36 #define __user_swpX_asm(data, addr, res, temp, B)               \
  37         __asm__ __volatile__(                                   \
  38         "       mov             %2, %1\n"                       \
  39         "0:     ldrex"B"        %1, [%3]\n"                     \
  40         "1:     strex"B"        %0, %2, [%3]\n"                 \
  41         "       cmp             %0, #0\n"                       \
  42         "       movne           %0, %4\n"                       \
  43         "2:\n"                                                  \
  44         "       .section         .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
  77 static unsigned long swpcounter;
  78 static unsigned long swpbcounter;
  79 static unsigned long abtcounter;
  80 static pid_t         previous_pid;
  81
  82 #ifdef CONFIG_PROC_FS
  83 static 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
  93 static int proc_status_open(struct inode *inode, struct file *file)
  94 {
  95         return single_open(file, proc_status_show, PDE_DATA(inode));
  96 }
  97
  98 static const struct file_operations proc_status_fops = {
  99         .open           = proc_status_open,
 100         .read           = seq_read,
 101         .llseek         = seq_lseek,
 102         .release        = single_release,
 103 };
 104 #endif
 105
 106 /*
 107  * Set up process info to signal segmentation fault - called on access error.
 108  */
 109 static void set_segfault(struct pt_regs *regs, unsigned long addr)
 110 {
 111         siginfo_t info;
 112
 113         down_read(&current->mm->mmap_sem);
 114         if (find_vma(current->mm, addr) == NULL)
 115                 info.si_code = SEGV_MAPERR;
 116         else
 117                 info.si_code = SEGV_ACCERR;
 118         up_read(&current->mm->mmap_sem);
 119
 120         info.si_signo = SIGSEGV;
 121         info.si_errno = 0;
 122         info.si_addr  = (void *) instruction_pointer(regs);
 123
 124         pr_debug("SWP{B} emulation: access caused memory abort!\n");
 125         arm_notify_die("Illegal memory access", regs, &info, 0, 0);
 126
 127         abtcounter++;
 128 }
 129
 130 static int emulate_swpX(unsigned int address, unsigned int *data,
 131                         unsigned int type)
 132 {
 133         unsigned int res = 0;
 134
 135         if ((type != TYPE_SWPB) && (address & 0x3)) {
 136                 /* SWP to unaligned address not permitted */
 137                 pr_debug("SWP instruction on unaligned pointer!\n");
 138                 return -EFAULT;
 139         }
 140
 141         while (1) {
 142                 unsigned long temp;
 143
 144                 /*
 145                  * Barrier required between accessing protected resource and
 146                  * releasing a lock for it. Legacy code might not have done
 147                  * this, and we cannot determine that this is not the case
 148                  * being emulated, so insert always.
 149                  */
 150                 smp_mb();
 151
 152                 if (type == TYPE_SWPB)
 153                         __user_swpb_asm(*data, address, res, temp);
 154                 else
 155                         __user_swp_asm(*data, address, res, temp);
 156
 157                 if (likely(res != -EAGAIN) || signal_pending(current))
 158                         break;
 159
 160                 cond_resched();
 161         }
 162
 163         if (res == 0) {
 164                 /*
 165                  * Barrier also required between acquiring a lock for a
 166                  * protected resource and accessing the resource. Inserted for
 167                  * same reason as above.
 168                  */
 169                 smp_mb();
 170
 171                 if (type == TYPE_SWPB)
 172                         swpbcounter++;
 173                 else
 174                         swpcounter++;
 175         }
 176
 177         return res;
 178 }
 179
 180 /*
 181  * swp_handler logs the id of calling process, dissects the instruction, sanity
 182  * checks the memory location, calls emulate_swpX for the actual operation and
 183  * deals with fixup/error handling before returning
 184  */
 185 static int swp_handler(struct pt_regs *regs, unsigned int instr)
 186 {
 187         unsigned int address, destreg, data, type;
 188         unsigned int res = 0;
 189
 190         perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
 191
 192         res = arm_check_condition(instr, regs->ARM_cpsr);
 193         switch (res) {
 194         case ARM_OPCODE_CONDTEST_PASS:
 195                 break;
 196         case ARM_OPCODE_CONDTEST_FAIL:
 197                 /* Condition failed - return to next instruction */
 198                 regs->ARM_pc += 4;
 199                 return 0;
 200         case ARM_OPCODE_CONDTEST_UNCOND:
 201                 /* If unconditional encoding - not a SWP, undef */
 202                 return -EFAULT;
 203         default:
 204                 return -EINVAL;
 205         }
 206
 207         if (current->pid != previous_pid) {
 208                 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
 209                          current->comm, (unsigned long)current->pid);
 210                 previous_pid = current->pid;
 211         }
 212
 213         address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
 214         data    = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
 215         destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
 216
 217         type = instr & TYPE_SWPB;
 218
 219         pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
 220                  EXTRACT_REG_NUM(instr, RN_OFFSET), address,
 221                  destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
 222
 223         /* Check access in reasonable access range for both SWP and SWPB */
 224         if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
 225                 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
 226                          (void *)address);
 227                 res = -EFAULT;
 228         } else {
 229                 res = emulate_swpX(address, &data, type);
 230         }
 231
 232         if (res == 0) {
 233                 /*
 234                  * On successful emulation, revert the adjustment to the PC
 235                  * made in kernel/traps.c in order to resume execution at the
 236                  * instruction following the SWP{B}.
 237                  */
 238                 regs->ARM_pc += 4;
 239                 regs->uregs[destreg] = data;
 240         } else if (res == -EFAULT) {
 241                 /*
 242                  * Memory errors do not mean emulation failed.
 243                  * Set up signal info to return SEGV, then return OK
 244                  */
 245                 set_segfault(regs, address);
 246         }
 247
 248         return 0;
 249 }
 250
 251 /*
 252  * Only emulate SWP/SWPB executed in ARM state/User mode.
 253  * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
 254  */
 255 static struct undef_hook swp_hook = {
 256         .instr_mask = 0x0fb00ff0,
 257         .instr_val  = 0x01000090,
 258         .cpsr_mask  = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
 259         .cpsr_val   = USR_MODE,
 260         .fn         = swp_handler
 261 };
 262
 263 /*
 264  * Register handler and create status file in /proc/cpu
 265  * Invoked as late_initcall, since not needed before init spawned.
 266  */
 267 static int __init swp_emulation_init(void)
 268 {
 269 #ifdef CONFIG_PROC_FS
 270         if (!proc_create("cpu/swp_emulation", S_IRUGO, NULL, &proc_status_fops))
 271                 return -ENOMEM;
 272 #endif /* CONFIG_PROC_FS */
 273
 274         printk(KERN_NOTICE "Registering SWP/SWPB emulation handler\n");
 275         register_undef_hook(&swp_hook);
 276
 277         return 0;
 278 }
 279
 280 late_initcall(swp_emulation_init);