arch/arm/kernel/swp_emulate.c

   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         ".arch armv7-a\n"                                       \
  38         "0:     ldrex"B"        %2, [%3]\n"                     \
  39         "1:     strex"B"        %0, %1, [%3]\n"                 \
  40         "       cmp             %0, #0\n"                       \
  41         "       moveq           %1, %2\n"                       \
  42         "       movne           %0, %4\n"                       \
  43         "2:\n"                                                  \
  44         "       .section         .text.fixup,\"ax\"\n"          \
  45         "       .align          2\n"                            \
  46         "3:     mov             %0, %5\n"                       \
  47         "       b               2b\n"                           \
  48         "       .previous\n"                                    \
  49         "       .section         __ex_table,\"a\"\n"            \
  50         "       .align          3\n"                            \
  51         "       .long           0b, 3b\n"                       \
  52         "       .long           1b, 3b\n"                       \
  53         "       .previous"                                      \
  54         : "=&r" (res), "+r" (data), "=&r" (temp)                \
  55         : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT)              \
  56         : "cc", "memory")
  57
  58 #define __user_swp_asm(data, addr, res, temp) \
  59         __user_swpX_asm(data, addr, res, temp, "")
  60 #define __user_swpb_asm(data, addr, res, temp) \
  61         __user_swpX_asm(data, addr, res, temp, "b")
  62
  63 /*
  64  * Macros/defines for extracting register numbers from instruction.
  65  */
  66 #define EXTRACT_REG_NUM(instruction, offset) \
  67         (((instruction) & (0xf << (offset))) >> (offset))
  68 #define RN_OFFSET  16
  69 #define RT_OFFSET  12
  70 #define RT2_OFFSET  0
  71 /*
  72  * Bit 22 of the instruction encoding distinguishes between
  73  * the SWP and SWPB variants (bit set means SWPB).
  74  */
  75 #define TYPE_SWPB (1 << 22)
  76
  77 static unsigned long swpcounter;
  78 static unsigned long swpbcounter;
  79 static unsigned long abtcounter;
  80 static pid_t         previous_pid;
  81
  82 #ifdef CONFIG_PROC_FS
  83 static int proc_status_show(struct seq_file *m, void *v)
  84 {
  85         seq_printf(m, "Emulated SWP:\t\t%lu\n", swpcounter);
  86         seq_printf(m, "Emulated SWPB:\t\t%lu\n", swpbcounter);
  87         seq_printf(m, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
  88         if (previous_pid != 0)
  89                 seq_printf(m, "Last process:\t\t%d\n", previous_pid);
  90         return 0;
  91 }
  92 #endif
  93
  94 /*
  95  * Set up process info to signal segmentation fault - called on access error.
  96  */
  97 static void set_segfault(struct pt_regs *regs, unsigned long addr)
  98 {
  99         int si_code;
 100
 101         mmap_read_lock(current->mm);
 102         if (find_vma(current->mm, addr) == NULL)
 103                 si_code = SEGV_MAPERR;
 104         else
 105                 si_code = SEGV_ACCERR;
 106         mmap_read_unlock(current->mm);
 107
 108         pr_debug("SWP{B} emulation: access caused memory abort!\n");
 109         arm_notify_die("Illegal memory access", regs,
 110                        SIGSEGV, si_code,
 111                        (void __user *)instruction_pointer(regs),
 112                        0, 0);
 113
 114         abtcounter++;
 115 }
 116
 117 static int emulate_swpX(unsigned int address, unsigned int *data,
 118                         unsigned int type)
 119 {
 120         unsigned int res = 0;
 121
 122         if ((type != TYPE_SWPB) && (address & 0x3)) {
 123                 /* SWP to unaligned address not permitted */
 124                 pr_debug("SWP instruction on unaligned pointer!\n");
 125                 return -EFAULT;
 126         }
 127
 128         while (1) {
 129                 unsigned long temp;
 130                 unsigned int __ua_flags;
 131
 132                 __ua_flags = uaccess_save_and_enable();
 133                 if (type == TYPE_SWPB)
 134                         __user_swpb_asm(*data, address, res, temp);
 135                 else
 136                         __user_swp_asm(*data, address, res, temp);
 137                 uaccess_restore(__ua_flags);
 138
 139                 if (likely(res != -EAGAIN) || signal_pending(current))
 140                         break;
 141
 142                 cond_resched();
 143         }
 144
 145         if (res == 0) {
 146                 if (type == TYPE_SWPB)
 147                         swpbcounter++;
 148                 else
 149                         swpcounter++;
 150         }
 151
 152         return res;
 153 }
 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
 165         perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
 166
 167         res = arm_check_condition(instr, regs->ARM_cpsr);
 168         switch (res) {
 169         case ARM_OPCODE_CONDTEST_PASS:
 170                 break;
 171         case ARM_OPCODE_CONDTEST_FAIL:
 172                 /* Condition failed - return to next instruction */
 173                 regs->ARM_pc += 4;
 174                 return 0;
 175         case ARM_OPCODE_CONDTEST_UNCOND:
 176                 /* If unconditional encoding - not a SWP, undef */
 177                 return -EFAULT;
 178         default:
 179                 return -EINVAL;
 180         }
 181
 182         if (current->pid != previous_pid) {
 183                 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
 184                          current->comm, (unsigned long)current->pid);
 185                 previous_pid = current->pid;
 186         }
 187
 188         address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
 189         data    = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
 190         destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
 191
 192         type = instr & TYPE_SWPB;
 193
 194         pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
 195                  EXTRACT_REG_NUM(instr, RN_OFFSET), address,
 196                  destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
 197
 198         /* Check access in reasonable access range for both SWP and SWPB */
 199         if (!access_ok((void __user *)(address & ~3), 4)) {
 200                 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
 201                          (void *)address);
 202                 res = -EFAULT;
 203         } else {
 204                 res = emulate_swpX(address, &data, type);
 205         }
 206
 207         if (res == 0) {
 208                 /*
 209                  * On successful emulation, revert the adjustment to the PC
 210                  * made in kernel/traps.c in order to resume execution at the
 211                  * instruction following the SWP{B}.
 212                  */
 213                 regs->ARM_pc += 4;
 214                 regs->uregs[destreg] = data;
 215         } else if (res == -EFAULT) {
 216                 /*
 217                  * Memory errors do not mean emulation failed.
 218                  * Set up signal info to return SEGV, then return OK
 219                  */
 220                 set_segfault(regs, address);
 221         }
 222
 223         return 0;
 224 }
 225
 226 /*
 227  * Only emulate SWP/SWPB executed in ARM state/User mode.
 228  * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
 229  */
 230 static struct undef_hook swp_hook = {
 231         .instr_mask = 0x0fb00ff0,
 232         .instr_val  = 0x01000090,
 233         .cpsr_mask  = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
 234         .cpsr_val   = USR_MODE,
 235         .fn         = swp_handler
 236 };
 237
 238 /*
 239  * Register handler and create status file in /proc/cpu
 240  * Invoked as late_initcall, since not needed before init spawned.
 241  */
 242 static int __init swp_emulation_init(void)
 243 {
 244         if (cpu_architecture() < CPU_ARCH_ARMv7)
 245                 return 0;
 246
 247 #ifdef CONFIG_PROC_FS
 248         if (!proc_create_single("cpu/swp_emulation", S_IRUGO, NULL,
 249                         proc_status_show))
 250                 return -ENOMEM;
 251 #endif /* CONFIG_PROC_FS */
 252
 253         pr_notice("Registering SWP/SWPB emulation handler\n");
 254         register_undef_hook(&swp_hook);
 255
 256         return 0;
 257 }
 258
 259 late_initcall(swp_emulation_init);