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/system_info.h>
  31 #include <asm/traps.h>
  32 #include <asm/uaccess.h>
  33
  34 /*
  35  * Error-checking SWP macros implemented using ldrex{b}/strex{b}
  36  */
  37 #define __user_swpX_asm(data, addr, res, temp, B)               \
  38         __asm__ __volatile__(                                   \
  39         "       mov             %2, %1\n"                       \
  40         "0:     ldrex"B"        %1, [%3]\n"                     \
  41         "1:     strex"B"        %0, %2, [%3]\n"                 \
  42         "       cmp             %0, #0\n"                       \
  43         "       movne           %0, %4\n"                       \
  44         "2:\n"                                                  \
  45         "       .section         .text.fixup,\"ax\"\n"          \
  46         "       .align          2\n"                            \
  47         "3:     mov             %0, %5\n"                       \
  48         "       b               2b\n"                           \
  49         "       .previous\n"                                    \
  50         "       .section         __ex_table,\"a\"\n"            \
  51         "       .align          3\n"                            \
  52         "       .long           0b, 3b\n"                       \
  53         "       .long           1b, 3b\n"                       \
  54         "       .previous"                                      \
  55         : "=&r" (res), "+r" (data), "=&r" (temp)                \
  56         : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT)              \
  57         : "cc", "memory")
  58
  59 #define __user_swp_asm(data, addr, res, temp) \
  60         __user_swpX_asm(data, addr, res, temp, "")
  61 #define __user_swpb_asm(data, addr, res, temp) \
  62         __user_swpX_asm(data, addr, res, temp, "b")
  63
  64 /*
  65  * Macros/defines for extracting register numbers from instruction.
  66  */
  67 #define EXTRACT_REG_NUM(instruction, offset) \
  68         (((instruction) & (0xf << (offset))) >> (offset))
  69 #define RN_OFFSET  16
  70 #define RT_OFFSET  12
  71 #define RT2_OFFSET  0
  72 /*
  73  * Bit 22 of the instruction encoding distinguishes between
  74  * the SWP and SWPB variants (bit set means SWPB).
  75  */
  76 #define TYPE_SWPB (1 << 22)
  77
  78 static unsigned long swpcounter;
  79 static unsigned long swpbcounter;
  80 static unsigned long abtcounter;
  81 static pid_t         previous_pid;
  82
  83 #ifdef CONFIG_PROC_FS
  84 static int proc_status_show(struct seq_file *m, void *v)
  85 {
  86         seq_printf(m, "Emulated SWP:\t\t%lu\n", swpcounter);
  87         seq_printf(m, "Emulated SWPB:\t\t%lu\n", swpbcounter);
  88         seq_printf(m, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
  89         if (previous_pid != 0)
  90                 seq_printf(m, "Last process:\t\t%d\n", previous_pid);
  91         return 0;
  92 }
  93
  94 static int proc_status_open(struct inode *inode, struct file *file)
  95 {
  96         return single_open(file, proc_status_show, PDE_DATA(inode));
  97 }
  98
  99 static const struct file_operations proc_status_fops = {
 100         .open           = proc_status_open,
 101         .read           = seq_read,
 102         .llseek         = seq_lseek,
 103         .release        = single_release,
 104 };
 105 #endif
 106
 107 /*
 108  * Set up process info to signal segmentation fault - called on access error.
 109  */
 110 static void set_segfault(struct pt_regs *regs, unsigned long addr)
 111 {
 112         siginfo_t info;
 113
 114         down_read(&current->mm->mmap_sem);
 115         if (find_vma(current->mm, addr) == NULL)
 116                 info.si_code = SEGV_MAPERR;
 117         else
 118                 info.si_code = SEGV_ACCERR;
 119         up_read(&current->mm->mmap_sem);
 120
 121         info.si_signo = SIGSEGV;
 122         info.si_errno = 0;
 123         info.si_addr  = (void *) instruction_pointer(regs);
 124
 125         pr_debug("SWP{B} emulation: access caused memory abort!\n");
 126         arm_notify_die("Illegal memory access", regs, &info, 0, 0);
 127
 128         abtcounter++;
 129 }
 130
 131 static int emulate_swpX(unsigned int address, unsigned int *data,
 132                         unsigned int type)
 133 {
 134         unsigned int res = 0;
 135
 136         if ((type != TYPE_SWPB) && (address & 0x3)) {
 137                 /* SWP to unaligned address not permitted */
 138                 pr_debug("SWP instruction on unaligned pointer!\n");
 139                 return -EFAULT;
 140         }
 141
 142         while (1) {
 143                 unsigned long temp;
 144                 unsigned int __ua_flags;
 145
 146                 __ua_flags = uaccess_save_and_enable();
 147                 if (type == TYPE_SWPB)
 148                         __user_swpb_asm(*data, address, res, temp);
 149                 else
 150                         __user_swp_asm(*data, address, res, temp);
 151                 uaccess_restore(__ua_flags);
 152
 153                 if (likely(res != -EAGAIN) || signal_pending(current))
 154                         break;
 155
 156                 cond_resched();
 157         }
 158
 159         if (res == 0) {
 160                 if (type == TYPE_SWPB)
 161                         swpbcounter++;
 162                 else
 163                         swpcounter++;
 164         }
 165
 166         return res;
 167 }
 168
 169 /*
 170  * swp_handler logs the id of calling process, dissects the instruction, sanity
 171  * checks the memory location, calls emulate_swpX for the actual operation and
 172  * deals with fixup/error handling before returning
 173  */
 174 static int swp_handler(struct pt_regs *regs, unsigned int instr)
 175 {
 176         unsigned int address, destreg, data, type;
 177         unsigned int res = 0;
 178
 179         perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
 180
 181         res = arm_check_condition(instr, regs->ARM_cpsr);
 182         switch (res) {
 183         case ARM_OPCODE_CONDTEST_PASS:
 184                 break;
 185         case ARM_OPCODE_CONDTEST_FAIL:
 186                 /* Condition failed - return to next instruction */
 187                 regs->ARM_pc += 4;
 188                 return 0;
 189         case ARM_OPCODE_CONDTEST_UNCOND:
 190                 /* If unconditional encoding - not a SWP, undef */
 191                 return -EFAULT;
 192         default:
 193                 return -EINVAL;
 194         }
 195
 196         if (current->pid != previous_pid) {
 197                 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
 198                          current->comm, (unsigned long)current->pid);
 199                 previous_pid = current->pid;
 200         }
 201
 202         address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
 203         data    = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
 204         destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
 205
 206         type = instr & TYPE_SWPB;
 207
 208         pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
 209                  EXTRACT_REG_NUM(instr, RN_OFFSET), address,
 210                  destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
 211
 212         /* Check access in reasonable access range for both SWP and SWPB */
 213         if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
 214                 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
 215                          (void *)address);
 216                 res = -EFAULT;
 217         } else {
 218                 res = emulate_swpX(address, &data, type);
 219         }
 220
 221         if (res == 0) {
 222                 /*
 223                  * On successful emulation, revert the adjustment to the PC
 224                  * made in kernel/traps.c in order to resume execution at the
 225                  * instruction following the SWP{B}.
 226                  */
 227                 regs->ARM_pc += 4;
 228                 regs->uregs[destreg] = data;
 229         } else if (res == -EFAULT) {
 230                 /*
 231                  * Memory errors do not mean emulation failed.
 232                  * Set up signal info to return SEGV, then return OK
 233                  */
 234                 set_segfault(regs, address);
 235         }
 236
 237         return 0;
 238 }
 239
 240 /*
 241  * Only emulate SWP/SWPB executed in ARM state/User mode.
 242  * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
 243  */
 244 static struct undef_hook swp_hook = {
 245         .instr_mask = 0x0fb00ff0,
 246         .instr_val  = 0x01000090,
 247         .cpsr_mask  = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
 248         .cpsr_val   = USR_MODE,
 249         .fn         = swp_handler
 250 };
 251
 252 /*
 253  * Register handler and create status file in /proc/cpu
 254  * Invoked as late_initcall, since not needed before init spawned.
 255  */
 256 static int __init swp_emulation_init(void)
 257 {
 258         if (cpu_architecture() < CPU_ARCH_ARMv7)
 259                 return 0;
 260
 261 #ifdef CONFIG_PROC_FS
 262         if (!proc_create("cpu/swp_emulation", S_IRUGO, NULL, &proc_status_fops))
 263                 return -ENOMEM;
 264 #endif /* CONFIG_PROC_FS */
 265
 266         pr_notice("Registering SWP/SWPB emulation handler\n");
 267         register_undef_hook(&swp_hook);
 268
 269         return 0;
 270 }
 271
 272 late_initcall(swp_emulation_init);