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/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
  79 static unsigned long swpcounter;
  80 static unsigned long swpbcounter;
  81 static unsigned long abtcounter;
  82 static pid_t         previous_pid;
  83
  84 #ifdef CONFIG_PROC_FS
  85 static 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
  95 static int proc_status_open(struct inode *inode, struct file *file)
  96 {
  97         return single_open(file, proc_status_show, PDE_DATA(inode));
  98 }
  99
 100 static 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  */
 111 static 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
 132 static 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  */
 175 static 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  */
 245 static 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  */
 257 static 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
 273 late_initcall(swp_emulation_init);