swp_emulate.c 7.3 KB

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