// SPDX-License-Identifier: GPL-2.0-only
/*
* linux/arch/arm/kernel/swp_emulate.c
*
* Copyright (C) 2009 ARM Limited
* __user_* functions adapted from include/asm/uaccess.h
*
* Implements emulation of the SWP/SWPB instructions using load-exclusive and
* store-exclusive for processors that have them disabled (or future ones that
* might not implement them).
*
* Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>]
* Where: Rt = destination
* Rt2 = source
* Rn = address
*/
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/syscalls.h>
#include <linux/perf_event.h>
#include <asm/opcodes.h>
#include <asm/system_info.h>
#include <asm/traps.h>
#include <linux/uaccess.h>
/*
* Error-checking SWP macros implemented using ldrex{b}/strex{b}
*/
#define __user_swpX_asm(data, addr, res, temp, B) \
__asm__ __volatile__( \
".arch armv7-a\n" \
"0: ldrex"B" %2, [%3]\n" \
"1: strex"B" %0, %1, [%3]\n" \
" cmp %0, #0\n" \
" moveq %1, %2\n" \
" movne %0, %4\n" \
"2:\n" \
" .section .text.fixup,\"ax\"\n" \
" .align 2\n" \
"3: mov %0, %5\n" \
" b 2b\n" \
" .previous\n" \
" .section __ex_table,\"a\"\n" \
" .align 3\n" \
" .long 0b, 3b\n" \
" .long 1b, 3b\n" \
" .previous" \
: "=&r" (res), "+r" (data), "=&r" (temp) \
: "r" (addr), "i" (-EAGAIN), "i" (-EFAULT) \
: "cc", "memory")
#define __user_swp_asm(data, addr, res, temp) \
__user_swpX_asm(data, addr, res, temp, "")
#define __user_swpb_asm(data, addr, res, temp) \
__user_swpX_asm(data, addr, res, temp, "b")
/*
* Macros/defines for extracting register numbers from instruction.
*/
#define EXTRACT_REG_NUM(instruction, offset) \
(((instruction) & (0xf << (offset))) >> (offset))
#define RN_OFFSET 16
#define RT_OFFSET 12
#define RT2_OFFSET 0
/*
* Bit 22 of the instruction encoding distinguishes between
* the SWP and SWPB variants (bit set means SWPB).
*/
#define TYPE_SWPB (1 << 22)
static unsigned long swpcounter;
static unsigned long swpbcounter;
static unsigned long abtcounter;
static pid_t previous_pid;
#ifdef CONFIG_PROC_FS
static int proc_status_show(struct seq_file *m, void *v)
{
seq_printf(m, "Emulated SWP:\t\t%lu\n", swpcounter);
seq_printf(m, "Emulated SWPB:\t\t%lu\n", swpbcounter);
seq_printf(m, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
if (previous_pid != 0)
seq_printf(m, "Last process:\t\t%d\n", previous_pid);
return 0;
}
#endif
/*
* Set up process info to signal segmentation fault - called on access error.
*/
static void set_segfault(struct pt_regs *regs, unsigned long addr)
{
int si_code;
mmap_read_lock(current->mm);
if (find_vma(current->mm, addr) == NULL)
si_code = SEGV_MAPERR;
else
si_code = SEGV_ACCERR;
mmap_read_unlock(current->mm);
pr_debug("SWP{B} emulation: access caused memory abort!\n");
arm_notify_die("Illegal memory access", regs,
SIGSEGV, si_code,
(void __user *)instruction_pointer(regs),
0, 0);
abtcounter++;
}
static int emulate_swpX(unsigned int address, unsigned int *data,
unsigned int type)
{
unsigned int res = 0;
if ((type != TYPE_SWPB) && (address & 0x3)) {
/* SWP to unaligned address not permitted */
pr_debug("SWP instruction on unaligned pointer!\n");
return -EFAULT;
}
while (1) {
unsigned long temp;
unsigned int __ua_flags;
__ua_flags = uaccess_save_and_enable();
if (type == TYPE_SWPB)
__user_swpb_asm(*data, address, res, temp);
else
__user_swp_asm(*data, address, res, temp);
uaccess_restore(__ua_flags);
if (likely(res != -EAGAIN) || signal_pending(current))
break;
cond_resched();
}
if (res == 0) {
if (type == TYPE_SWPB)
swpbcounter++;
else
swpcounter++;
}
return res;
}
/*
* swp_handler logs the id of calling process, dissects the instruction, sanity
* checks the memory location, calls emulate_swpX for the actual operation and
* deals with fixup/error handling before returning
*/
static int swp_handler(struct pt_regs *regs, unsigned int instr)
{
unsigned int address, destreg, data, type;
unsigned int res = 0;
perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->ARM_pc);
res = arm_check_condition(instr, regs->ARM_cpsr);
switch (res) {
case ARM_OPCODE_CONDTEST_PASS:
break;
case ARM_OPCODE_CONDTEST_FAIL:
/* Condition failed - return to next instruction */
regs->ARM_pc += 4;
return 0;
case ARM_OPCODE_CONDTEST_UNCOND:
/* If unconditional encoding - not a SWP, undef */
return -EFAULT;
default:
return -EINVAL;
}
if (current->pid != previous_pid) {
pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
current->comm, (unsigned long)current->pid);
previous_pid = current->pid;
}
address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
data = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);
type = instr & TYPE_SWPB;
pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
EXTRACT_REG_NUM(instr, RN_OFFSET), address,
destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);
/* Check access in reasonable access range for both SWP and SWPB */
if (!access_ok((void __user *)(address & ~3), 4)) {
pr_debug("SWP{B} emulation: access to %p not allowed!\n",
(void *)address);
res = -EFAULT;
} else {
res = emulate_swpX(address, &data, type);
}
if (res == 0) {
/*
* On successful emulation, revert the adjustment to the PC
* made in kernel/traps.c in order to resume execution at the
* instruction following the SWP{B}.
*/
regs->ARM_pc += 4;
regs->uregs[destreg] = data;
} else if (res == -EFAULT) {
/*
* Memory errors do not mean emulation failed.
* Set up signal info to return SEGV, then return OK
*/
set_segfault(regs, address);
}
return 0;
}
/*
* Only emulate SWP/SWPB executed in ARM state/User mode.
* The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
*/
static struct undef_hook swp_hook = {
.instr_mask = 0x0fb00ff0,
.instr_val = 0x01000090,
.cpsr_mask = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
.cpsr_val = USR_MODE,
.fn = swp_handler
};
/*
* Register handler and create status file in /proc/cpu
* Invoked as late_initcall, since not needed before init spawned.
*/
static int __init swp_emulation_init(void)
{
if (cpu_architecture() < CPU_ARCH_ARMv7)
return 0;
#ifdef CONFIG_PROC_FS
if (!proc_create_single("cpu/swp_emulation", S_IRUGO, NULL,
proc_status_show))
return -ENOMEM;
#endif /* CONFIG_PROC_FS */
pr_notice("Registering SWP/SWPB emulation handler\n");
register_undef_hook(&swp_hook);
return 0;
}
late_initcall(swp_emulation_init);