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/sched/mm.h>
  27#include <linux/syscalls.h>
  28#include <linux/perf_event.h>
  29
  30#include <asm/opcodes.h>
  31#include <asm/system_info.h>
  32#include <asm/traps.h>
  33#include <linux/uaccess.h>
  34
  35/*
  36 * Error-checking SWP macros implemented using ldrex{b}/strex{b}
  37 */
  38#define __user_swpX_asm(data, addr, res, temp, B)               \
  39        __asm__ __volatile__(                                   \
  40        "0:     ldrex"B"        %2, [%3]\n"                     \
  41        "1:     strex"B"        %0, %1, [%3]\n"                 \
  42        "       cmp             %0, #0\n"                       \
  43        "       moveq           %1, %2\n"                       \
  44        "       movne           %0, %4\n"                       \
  45        "2:\n"                                                  \
  46        "       .section         .text.fixup,\"ax\"\n"          \
  47        "       .align          2\n"                            \
  48        "3:     mov             %0, %5\n"                       \
  49        "       b               2b\n"                           \
  50        "       .previous\n"                                    \
  51        "       .section         __ex_table,\"a\"\n"            \
  52        "       .align          3\n"                            \
  53        "       .long           0b, 3b\n"                       \
  54        "       .long           1b, 3b\n"                       \
  55        "       .previous"                                      \
  56        : "=&r" (res), "+r" (data), "=&r" (temp)                \
  57        : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT)              \
  58        : "cc", "memory")
  59
  60#define __user_swp_asm(data, addr, res, temp) \
  61        __user_swpX_asm(data, addr, res, temp, "")
  62#define __user_swpb_asm(data, addr, res, temp) \
  63        __user_swpX_asm(data, addr, res, temp, "b")
  64
  65/*
  66 * Macros/defines for extracting register numbers from instruction.
  67 */
  68#define EXTRACT_REG_NUM(instruction, offset) \
  69        (((instruction) & (0xf << (offset))) >> (offset))
  70#define RN_OFFSET  16
  71#define RT_OFFSET  12
  72#define RT2_OFFSET  0
  73/*
  74 * Bit 22 of the instruction encoding distinguishes between
  75 * the SWP and SWPB variants (bit set means SWPB).
  76 */
  77#define TYPE_SWPB (1 << 22)
  78
  79static unsigned long swpcounter;
  80static unsigned long swpbcounter;
  81static unsigned long abtcounter;
  82static pid_t         previous_pid;
  83
  84#ifdef CONFIG_PROC_FS
  85static int proc_status_show(struct seq_file *m, void *v)
  86{
  87        seq_printf(m, "Emulated SWP:\t\t%lu\n", swpcounter);
  88        seq_printf(m, "Emulated SWPB:\t\t%lu\n", swpbcounter);
  89        seq_printf(m, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
  90        if (previous_pid != 0)
  91                seq_printf(m, "Last process:\t\t%d\n", previous_pid);
  92        return 0;
  93}
  94
  95static int proc_status_open(struct inode *inode, struct file *file)
  96{
  97        return single_open(file, proc_status_show, PDE_DATA(inode));
  98}
  99
 100static const struct file_operations proc_status_fops = {
 101        .open           = proc_status_open,
 102        .read           = seq_read,
 103        .llseek         = seq_lseek,
 104        .release        = single_release,
 105};
 106#endif
 107
 108/*
 109 * Set up process info to signal segmentation fault - called on access error.
 110 */
 111static void set_segfault(struct pt_regs *regs, unsigned long addr)
 112{
 113        siginfo_t info;
 114
 115        down_read(&current->mm->mmap_sem);
 116        if (find_vma(current->mm, addr) == NULL)
 117                info.si_code = SEGV_MAPERR;
 118        else
 119                info.si_code = SEGV_ACCERR;
 120        up_read(&current->mm->mmap_sem);
 121
 122        info.si_signo = SIGSEGV;
 123        info.si_errno = 0;
 124        info.si_addr  = (void *) instruction_pointer(regs);
 125
 126        pr_debug("SWP{B} emulation: access caused memory abort!\n");
 127        arm_notify_die("Illegal memory access", regs, &info, 0, 0);
 128
 129        abtcounter++;
 130}
 131
 132static int emulate_swpX(unsigned int address, unsigned int *data,
 133                        unsigned int type)
 134{
 135        unsigned int res = 0;
 136
 137        if ((type != TYPE_SWPB) && (address & 0x3)) {
 138                /* SWP to unaligned address not permitted */
 139                pr_debug("SWP instruction on unaligned pointer!\n");
 140                return -EFAULT;
 141        }
 142
 143        while (1) {
 144                unsigned long temp;
 145                unsigned int __ua_flags;
 146
 147                __ua_flags = uaccess_save_and_enable();
 148                if (type == TYPE_SWPB)
 149                        __user_swpb_asm(*data, address, res, temp);
 150                else
 151                        __user_swp_asm(*data, address, res, temp);
 152                uaccess_restore(__ua_flags);
 153
 154                if (likely(res != -EAGAIN) || signal_pending(current))
 155                        break;
 156
 157                cond_resched();
 158        }
 159
 160        if (res == 0) {
 161                if (type == TYPE_SWPB)
 162                        swpbcounter++;
 163                else
 164                        swpcounter++;
 165        }
 166
 167        return res;
 168}
 169
 170/*
 171 * swp_handler logs the id of calling process, dissects the instruction, sanity
 172 * checks the memory location, calls emulate_swpX for the actual operation and
 173 * deals with fixup/error handling before returning
 174 */
 175static int swp_handler(struct pt_regs *regs, unsigned int instr)
 176{
 177        unsigned int address, destreg, data, type;
 178        unsigned int res = 0;
 179
 180        perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
 181
 182        res = arm_check_condition(instr, regs->ARM_cpsr);
 183        switch (res) {
 184        case ARM_OPCODE_CONDTEST_PASS:
 185                break;
 186        case ARM_OPCODE_CONDTEST_FAIL:
 187                /* Condition failed - return to next instruction */
 188                regs->ARM_pc += 4;
 189                return 0;
 190        case ARM_OPCODE_CONDTEST_UNCOND:
 191                /* If unconditional encoding - not a SWP, undef */
 192                return -EFAULT;
 193        default:
 194                return -EINVAL;
 195        }
 196
 197        if (current->pid != previous_pid) {
 198                pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
 199                         current->comm, (unsigned long)current->pid);
 200                previous_pid = current->pid;
 201        }
 202
 203        address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
 204        data    = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
 205        destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
 206
 207        type = instr & TYPE_SWPB;
 208
 209        pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
 210                 EXTRACT_REG_NUM(instr, RN_OFFSET), address,
 211                 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
 212
 213        /* Check access in reasonable access range for both SWP and SWPB */
 214        if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
 215                pr_debug("SWP{B} emulation: access to %p not allowed!\n",
 216                         (void *)address);
 217                res = -EFAULT;
 218        } else {
 219                res = emulate_swpX(address, &data, type);
 220        }
 221
 222        if (res == 0) {
 223                /*
 224                 * On successful emulation, revert the adjustment to the PC
 225                 * made in kernel/traps.c in order to resume execution at the
 226                 * instruction following the SWP{B}.
 227                 */
 228                regs->ARM_pc += 4;
 229                regs->uregs[destreg] = data;
 230        } else if (res == -EFAULT) {
 231                /*
 232                 * Memory errors do not mean emulation failed.
 233                 * Set up signal info to return SEGV, then return OK
 234                 */
 235                set_segfault(regs, address);
 236        }
 237
 238        return 0;
 239}
 240
 241/*
 242 * Only emulate SWP/SWPB executed in ARM state/User mode.
 243 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
 244 */
 245static struct undef_hook swp_hook = {
 246        .instr_mask = 0x0fb00ff0,
 247        .instr_val  = 0x01000090,
 248        .cpsr_mask  = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
 249        .cpsr_val   = USR_MODE,
 250        .fn         = swp_handler
 251};
 252
 253/*
 254 * Register handler and create status file in /proc/cpu
 255 * Invoked as late_initcall, since not needed before init spawned.
 256 */
 257static int __init swp_emulation_init(void)
 258{
 259        if (cpu_architecture() < CPU_ARCH_ARMv7)
 260                return 0;
 261
 262#ifdef CONFIG_PROC_FS
 263        if (!proc_create("cpu/swp_emulation", S_IRUGO, NULL, &proc_status_fops))
 264                return -ENOMEM;
 265#endif /* CONFIG_PROC_FS */
 266
 267        pr_notice("Registering SWP/SWPB emulation handler\n");
 268        register_undef_hook(&swp_hook);
 269
 270        return 0;
 271}
 272
 273late_initcall(swp_emulation_init);
 274