2 * linux/arch/arm/kernel/swp_emulate.c
4 * Copyright (C) 2009 ARM Limited
5 * __user_* functions adapted from include/asm/uaccess.h
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.
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).
15 * Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>]
16 * Where: Rt = destination
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>
30 #include <asm/opcodes.h>
31 #include <asm/system_info.h>
32 #include <asm/traps.h>
33 #include <linux/uaccess.h>
36 * Error-checking SWP macros implemented using ldrex{b}/strex{b}
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" \
46 " .section .text.fixup,\"ax\"\n" \
51 " .section __ex_table,\"a\"\n" \
56 : "=&r" (res), "+r" (data), "=&r" (temp) \
57 : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \
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")
66 * Macros/defines for extracting register numbers from instruction.
68 #define EXTRACT_REG_NUM(instruction, offset) \
69 (((instruction) & (0xf << (offset))) >> (offset))
74 * Bit 22 of the instruction encoding distinguishes between
75 * the SWP and SWPB variants (bit set means SWPB).
77 #define TYPE_SWPB (1 << 22)
79 static unsigned long swpcounter;
80 static unsigned long swpbcounter;
81 static unsigned long abtcounter;
82 static pid_t previous_pid;
85 static int proc_status_show(struct seq_file *m, void *v)
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);
97 * Set up process info to signal segmentation fault - called on access error.
99 static void set_segfault(struct pt_regs *regs, unsigned long addr)
103 down_read(¤t->mm->mmap_sem);
104 if (find_vma(current->mm, addr) == NULL)
105 si_code = SEGV_MAPERR;
107 si_code = SEGV_ACCERR;
108 up_read(¤t->mm->mmap_sem);
110 pr_debug("SWP{B} emulation: access caused memory abort!\n");
111 arm_notify_die("Illegal memory access", regs,
113 (void __user *)instruction_pointer(regs),
119 static int emulate_swpX(unsigned int address, unsigned int *data,
122 unsigned int res = 0;
124 if ((type != TYPE_SWPB) && (address & 0x3)) {
125 /* SWP to unaligned address not permitted */
126 pr_debug("SWP instruction on unaligned pointer!\n");
132 unsigned int __ua_flags;
134 __ua_flags = uaccess_save_and_enable();
135 if (type == TYPE_SWPB)
136 __user_swpb_asm(*data, address, res, temp);
138 __user_swp_asm(*data, address, res, temp);
139 uaccess_restore(__ua_flags);
141 if (likely(res != -EAGAIN) || signal_pending(current))
148 if (type == TYPE_SWPB)
158 * swp_handler logs the id of calling process, dissects the instruction, sanity
159 * checks the memory location, calls emulate_swpX for the actual operation and
160 * deals with fixup/error handling before returning
162 static int swp_handler(struct pt_regs *regs, unsigned int instr)
164 unsigned int address, destreg, data, type;
165 unsigned int res = 0;
167 perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
169 res = arm_check_condition(instr, regs->ARM_cpsr);
171 case ARM_OPCODE_CONDTEST_PASS:
173 case ARM_OPCODE_CONDTEST_FAIL:
174 /* Condition failed - return to next instruction */
177 case ARM_OPCODE_CONDTEST_UNCOND:
178 /* If unconditional encoding - not a SWP, undef */
184 if (current->pid != previous_pid) {
185 pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
186 current->comm, (unsigned long)current->pid);
187 previous_pid = current->pid;
190 address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
191 data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
192 destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
194 type = instr & TYPE_SWPB;
196 pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
197 EXTRACT_REG_NUM(instr, RN_OFFSET), address,
198 destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
200 /* Check access in reasonable access range for both SWP and SWPB */
201 if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
202 pr_debug("SWP{B} emulation: access to %p not allowed!\n",
206 res = emulate_swpX(address, &data, type);
211 * On successful emulation, revert the adjustment to the PC
212 * made in kernel/traps.c in order to resume execution at the
213 * instruction following the SWP{B}.
216 regs->uregs[destreg] = data;
217 } else if (res == -EFAULT) {
219 * Memory errors do not mean emulation failed.
220 * Set up signal info to return SEGV, then return OK
222 set_segfault(regs, address);
229 * Only emulate SWP/SWPB executed in ARM state/User mode.
230 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
232 static struct undef_hook swp_hook = {
233 .instr_mask = 0x0fb00ff0,
234 .instr_val = 0x01000090,
235 .cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
236 .cpsr_val = USR_MODE,
241 * Register handler and create status file in /proc/cpu
242 * Invoked as late_initcall, since not needed before init spawned.
244 static int __init swp_emulation_init(void)
246 if (cpu_architecture() < CPU_ARCH_ARMv7)
249 #ifdef CONFIG_PROC_FS
250 if (!proc_create_single("cpu/swp_emulation", S_IRUGO, NULL,
253 #endif /* CONFIG_PROC_FS */
255 pr_notice("Registering SWP/SWPB emulation handler\n");
256 register_undef_hook(&swp_hook);
261 late_initcall(swp_emulation_init);