LXR linux/arch/arm/kernel/swp

   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
  77static unsigned long swpcounter;
  78static unsigned long swpbcounter;
  79static unsigned long abtcounter;
  80static pid_t         previous_pid;
  81
  82#ifdef CONFIG_PROC_FS
  83static 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
  93static int proc_status_open(struct inode *inode, struct file *file)
  94{
  95        return single_open(file, proc_status_show, PDE_DATA(inode));
  96}
  97
  98static 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 */
 109static 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
 130static 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 */
 185static 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 */
 255static 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 */
 267static 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
 280late_initcall(swp_emulation_init);
 281