LXR linux/arch/arm/kernel/swp

   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
  76static unsigned long swpcounter;
  77static unsigned long swpbcounter;
  78static unsigned long abtcounter;
  79static pid_t         previous_pid;
  80
  81#ifdef CONFIG_PROC_FS
  82static 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 */
  96static 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
 116static 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 */
 159static 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 */
 229static 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 */
 241static 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
 258late_initcall(swp_emulation_init);
 259