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/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        "0:     ldrex"B"        %2, [%3]\n"                     \
  40        "1:     strex"B"        %0, %1, [%3]\n"                 \
  41        "       cmp             %0, #0\n"                       \
  42        "       moveq           %1, %2\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
  78static unsigned long swpcounter;
  79static unsigned long swpbcounter;
  80static unsigned long abtcounter;
  81static pid_t         previous_pid;
  82
  83#ifdef CONFIG_PROC_FS
  84static 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
  94static int proc_status_open(struct inode *inode, struct file *file)
  95{
  96        return single_open(file, proc_status_show, PDE_DATA(inode));
  97}
  98
  99static 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 */
 110static 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
 131static 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 */
 174static 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 */
 244static 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 */
 256static 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
 272late_initcall(swp_emulation_init);
 273