root/arch/arm/kernel/swp_emulate.c

DEFINITIONS

1. proc_status_show
2. set_segfault
3. emulate_swpX
4. swp_handler
5. swp_emulation_init

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  linux/arch/arm/kernel/swp_emulate.c
   4  *
   5  *  Copyright (C) 2009 ARM Limited
   6  *  __user_* functions adapted from include/asm/uaccess.h
   7  *
   8  *  Implements emulation of the SWP/SWPB instructions using load-exclusive and
   9  *  store-exclusive for processors that have them disabled (or future ones that
  10  *  might not implement them).
  11  *
  12  *  Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>]
  13  *  Where: Rt  = destination
  14  *         Rt2 = source
  15  *         Rn  = address
  16  */
  17 
  18 #include <linux/init.h>
  19 #include <linux/kernel.h>
  20 #include <linux/proc_fs.h>
  21 #include <linux/seq_file.h>
  22 #include <linux/sched.h>
  23 #include <linux/sched/mm.h>
  24 #include <linux/syscalls.h>
  25 #include <linux/perf_event.h>
  26 
  27 #include <asm/opcodes.h>
  28 #include <asm/system_info.h>
  29 #include <asm/traps.h>
  30 #include <linux/uaccess.h>
  31 
  32 /*
  33  * Error-checking SWP macros implemented using ldrex{b}/strex{b}
  34  */
  35 #define __user_swpX_asm(data, addr, res, temp, B)               \
  36         __asm__ __volatile__(                                   \
  37         "0:     ldrex"B"        %2, [%3]\n"                     \
  38         "1:     strex"B"        %0, %1, [%3]\n"                 \
  39         "       cmp             %0, #0\n"                       \
  40         "       moveq           %1, %2\n"                       \
  41         "       movne           %0, %4\n"                       \
  42         "2:\n"                                                  \
  43         "       .section         .text.fixup,\"ax\"\n"          \
  44         "       .align          2\n"                            \
  45         "3:     mov             %0, %5\n"                       \
  46         "       b               2b\n"                           \
  47         "       .previous\n"                                    \
  48         "       .section         __ex_table,\"a\"\n"            \
  49         "       .align          3\n"                            \
  50         "       .long           0b, 3b\n"                       \
  51         "       .long           1b, 3b\n"                       \
  52         "       .previous"                                      \
  53         : "=&r" (res), "+r" (data), "=&r" (temp)                \
  54         : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT)              \
  55         : "cc", "memory")
  56 
  57 #define __user_swp_asm(data, addr, res, temp) \
  58         __user_swpX_asm(data, addr, res, temp, "")
  59 #define __user_swpb_asm(data, addr, res, temp) \
  60         __user_swpX_asm(data, addr, res, temp, "b")
  61 
  62 /*
  63  * Macros/defines for extracting register numbers from instruction.
  64  */
  65 #define EXTRACT_REG_NUM(instruction, offset) \
  66         (((instruction) & (0xf << (offset))) >> (offset))
  67 #define RN_OFFSET  16
  68 #define RT_OFFSET  12
  69 #define RT2_OFFSET  0
  70 /*
  71  * Bit 22 of the instruction encoding distinguishes between
  72  * the SWP and SWPB variants (bit set means SWPB).
  73  */
  74 #define TYPE_SWPB (1 << 22)
  75 
  76 static unsigned long swpcounter;
  77 static unsigned long swpbcounter;
  78 static unsigned long abtcounter;
  79 static pid_t         previous_pid;
  80 
  81 #ifdef CONFIG_PROC_FS
  82 static int proc_status_show(struct seq_file *m, void *v)
  83 {
  84         seq_printf(m, "Emulated SWP:\t\t%lu\n", swpcounter);
  85         seq_printf(m, "Emulated SWPB:\t\t%lu\n", swpbcounter);
  86         seq_printf(m, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
  87         if (previous_pid != 0)
  88                 seq_printf(m, "Last process:\t\t%d\n", previous_pid);
  89         return 0;
  90 }
  91 #endif
  92 
  93 /*
  94  * Set up process info to signal segmentation fault - called on access error.
  95  */
  96 static void set_segfault(struct pt_regs *regs, unsigned long addr)
  97 {
  98         int si_code;
  99 
 100         down_read(&current->mm->mmap_sem);
 101         if (find_vma(current->mm, addr) == NULL)
 102                 si_code = SEGV_MAPERR;
 103         else
 104                 si_code = SEGV_ACCERR;
 105         up_read(&current->mm->mmap_sem);
 106 
 107         pr_debug("SWP{B} emulation: access caused memory abort!\n");
 108         arm_notify_die("Illegal memory access", regs,
 109                        SIGSEGV, si_code,
 110                        (void __user *)instruction_pointer(regs),
 111                        0, 0);
 112 
 113         abtcounter++;
 114 }
 115 
 116 static int emulate_swpX(unsigned int address, unsigned int *data,
 117                         unsigned int type)
 118 {
 119         unsigned int res = 0;
 120 
 121         if ((type != TYPE_SWPB) && (address & 0x3)) {
 122                 /* SWP to unaligned address not permitted */
 123                 pr_debug("SWP instruction on unaligned pointer!\n");
 124                 return -EFAULT;
 125         }
 126 
 127         while (1) {
 128                 unsigned long temp;
 129                 unsigned int __ua_flags;
 130 
 131                 __ua_flags = uaccess_save_and_enable();
 132                 if (type == TYPE_SWPB)
 133                         __user_swpb_asm(*data, address, res, temp);
 134                 else
 135                         __user_swp_asm(*data, address, res, temp);
 136                 uaccess_restore(__ua_flags);
 137 
 138                 if (likely(res != -EAGAIN) || signal_pending(current))
 139                         break;
 140 
 141                 cond_resched();
 142         }
 143 
 144         if (res == 0) {
 145                 if (type == TYPE_SWPB)
 146                         swpbcounter++;
 147                 else
 148                         swpcounter++;
 149         }
 150 
 151         return res;
 152 }
 153 
 154 /*
 155  * swp_handler logs the id of calling process, dissects the instruction, sanity
 156  * checks the memory location, calls emulate_swpX for the actual operation and
 157  * deals with fixup/error handling before returning
 158  */
 159 static int swp_handler(struct pt_regs *regs, unsigned int instr)
 160 {
 161         unsigned int address, destreg, data, type;
 162         unsigned int res = 0;
 163 
 164         perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
 165 
 166         res = arm_check_condition(instr, regs->ARM_cpsr);
 167         switch (res) {
 168         case ARM_OPCODE_CONDTEST_PASS:
 169                 break;
 170         case ARM_OPCODE_CONDTEST_FAIL:
 171                 /* Condition failed - return to next instruction */
 172                 regs->ARM_pc += 4;
 173                 return 0;
 174         case ARM_OPCODE_CONDTEST_UNCOND:
 175                 /* If unconditional encoding - not a SWP, undef */
 176                 return -EFAULT;
 177         default:
 178                 return -EINVAL;
 179         }
 180 
 181         if (current->pid != previous_pid) {
 182                 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
 183                          current->comm, (unsigned long)current->pid);
 184                 previous_pid = current->pid;
 185         }
 186 
 187         address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
 188         data    = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
 189         destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
 190 
 191         type = instr & TYPE_SWPB;
 192 
 193         pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
 194                  EXTRACT_REG_NUM(instr, RN_OFFSET), address,
 195                  destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
 196 
 197         /* Check access in reasonable access range for both SWP and SWPB */
 198         if (!access_ok((address & ~3), 4)) {
 199                 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
 200                          (void *)address);
 201                 res = -EFAULT;
 202         } else {
 203                 res = emulate_swpX(address, &data, type);
 204         }
 205 
 206         if (res == 0) {
 207                 /*
 208                  * On successful emulation, revert the adjustment to the PC
 209                  * made in kernel/traps.c in order to resume execution at the
 210                  * instruction following the SWP{B}.
 211                  */
 212                 regs->ARM_pc += 4;
 213                 regs->uregs[destreg] = data;
 214         } else if (res == -EFAULT) {
 215                 /*
 216                  * Memory errors do not mean emulation failed.
 217                  * Set up signal info to return SEGV, then return OK
 218                  */
 219                 set_segfault(regs, address);
 220         }
 221 
 222         return 0;
 223 }
 224 
 225 /*
 226  * Only emulate SWP/SWPB executed in ARM state/User mode.
 227  * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
 228  */
 229 static struct undef_hook swp_hook = {
 230         .instr_mask = 0x0fb00ff0,
 231         .instr_val  = 0x01000090,
 232         .cpsr_mask  = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
 233         .cpsr_val   = USR_MODE,
 234         .fn         = swp_handler
 235 };
 236 
 237 /*
 238  * Register handler and create status file in /proc/cpu
 239  * Invoked as late_initcall, since not needed before init spawned.
 240  */
 241 static int __init swp_emulation_init(void)
 242 {
 243         if (cpu_architecture() < CPU_ARCH_ARMv7)
 244                 return 0;
 245 
 246 #ifdef CONFIG_PROC_FS
 247         if (!proc_create_single("cpu/swp_emulation", S_IRUGO, NULL,
 248                         proc_status_show))
 249                 return -ENOMEM;
 250 #endif /* CONFIG_PROC_FS */
 251 
 252         pr_notice("Registering SWP/SWPB emulation handler\n");
 253         register_undef_hook(&swp_hook);
 254 
 255         return 0;
 256 }
 257 
 258 late_initcall(swp_emulation_init);