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#endif
  95
  96/*
  97 * Set up process info to signal segmentation fault - called on access error.
  98 */
  99static void set_segfault(struct pt_regs *regs, unsigned long addr)
 100{
 101        int si_code;
 102
 103        down_read(&current->mm->mmap_sem);
 104        if (find_vma(current->mm, addr) == NULL)
 105                si_code = SEGV_MAPERR;
 106        else
 107                si_code = SEGV_ACCERR;
 108        up_read(&current->mm->mmap_sem);
 109
 110        pr_debug("SWP{B} emulation: access caused memory abort!\n");
 111        arm_notify_die("Illegal memory access", regs,
 112                       SIGSEGV, si_code,
 113                       (void __user *)instruction_pointer(regs),
 114                       0, 0);
 115
 116        abtcounter++;
 117}
 118
 119static int emulate_swpX(unsigned int address, unsigned int *data,
 120                        unsigned int type)
 121{
 122        unsigned int res = 0;
 123
 124        if ((type != TYPE_SWPB) && (address & 0x3)) {
 125                /* SWP to unaligned address not permitted */
 126                pr_debug("SWP instruction on unaligned pointer!\n");
 127                return -EFAULT;
 128        }
 129
 130        while (1) {
 131                unsigned long temp;
 132                unsigned int __ua_flags;
 133
 134                __ua_flags = uaccess_save_and_enable();
 135                if (type == TYPE_SWPB)
 136                        __user_swpb_asm(*data, address, res, temp);
 137                else
 138                        __user_swp_asm(*data, address, res, temp);
 139                uaccess_restore(__ua_flags);
 140
 141                if (likely(res != -EAGAIN) || signal_pending(current))
 142                        break;
 143
 144                cond_resched();
 145        }
 146
 147        if (res == 0) {
 148                if (type == TYPE_SWPB)
 149                        swpbcounter++;
 150                else
 151                        swpcounter++;
 152        }
 153
 154        return res;
 155}
 156
 157/*
 158 * swp_handler logs the id of calling process, dissects the instruction, sanity
 159 * checks the memory location, calls emulate_swpX for the actual operation and
 160 * deals with fixup/error handling before returning
 161 */
 162static int swp_handler(struct pt_regs *regs, unsigned int instr)
 163{
 164        unsigned int address, destreg, data, type;
 165        unsigned int res = 0;
 166
 167        perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
 168
 169        res = arm_check_condition(instr, regs->ARM_cpsr);
 170        switch (res) {
 171        case ARM_OPCODE_CONDTEST_PASS:
 172                break;
 173        case ARM_OPCODE_CONDTEST_FAIL:
 174                /* Condition failed - return to next instruction */
 175                regs->ARM_pc += 4;
 176                return 0;
 177        case ARM_OPCODE_CONDTEST_UNCOND:
 178                /* If unconditional encoding - not a SWP, undef */
 179                return -EFAULT;
 180        default:
 181                return -EINVAL;
 182        }
 183
 184        if (current->pid != previous_pid) {
 185                pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
 186                         current->comm, (unsigned long)current->pid);
 187                previous_pid = current->pid;
 188        }
 189
 190        address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
 191        data    = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
 192        destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
 193
 194        type = instr & TYPE_SWPB;
 195
 196        pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
 197                 EXTRACT_REG_NUM(instr, RN_OFFSET), address,
 198                 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
 199
 200        /* Check access in reasonable access range for both SWP and SWPB */
 201        if (!access_ok((address & ~3), 4)) {
 202                pr_debug("SWP{B} emulation: access to %p not allowed!\n",
 203                         (void *)address);
 204                res = -EFAULT;
 205        } else {
 206                res = emulate_swpX(address, &data, type);
 207        }
 208
 209        if (res == 0) {
 210                /*
 211                 * On successful emulation, revert the adjustment to the PC
 212                 * made in kernel/traps.c in order to resume execution at the
 213                 * instruction following the SWP{B}.
 214                 */
 215                regs->ARM_pc += 4;
 216                regs->uregs[destreg] = data;
 217        } else if (res == -EFAULT) {
 218                /*
 219                 * Memory errors do not mean emulation failed.
 220                 * Set up signal info to return SEGV, then return OK
 221                 */
 222                set_segfault(regs, address);
 223        }
 224
 225        return 0;
 226}
 227
 228/*
 229 * Only emulate SWP/SWPB executed in ARM state/User mode.
 230 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
 231 */
 232static struct undef_hook swp_hook = {
 233        .instr_mask = 0x0fb00ff0,
 234        .instr_val  = 0x01000090,
 235        .cpsr_mask  = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
 236        .cpsr_val   = USR_MODE,
 237        .fn         = swp_handler
 238};
 239
 240/*
 241 * Register handler and create status file in /proc/cpu
 242 * Invoked as late_initcall, since not needed before init spawned.
 243 */
 244static int __init swp_emulation_init(void)
 245{
 246        if (cpu_architecture() < CPU_ARCH_ARMv7)
 247                return 0;
 248
 249#ifdef CONFIG_PROC_FS
 250        if (!proc_create_single("cpu/swp_emulation", S_IRUGO, NULL,
 251                        proc_status_show))
 252                return -ENOMEM;
 253#endif /* CONFIG_PROC_FS */
 254
 255        pr_notice("Registering SWP/SWPB emulation handler\n");
 256        register_undef_hook(&swp_hook);
 257
 258        return 0;
 259}
 260
 261late_initcall(swp_emulation_init);
 262