arch/arm64/kernel/armv8_deprecated.c

/*
 *  Copyright (C) 2014 ARM Limited
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/init.h>
#include <linux/list.h>
#include <linux/perf_event.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/sysctl.h>

#include <asm/insn.h>
#include <asm/opcodes.h>
#include <asm/system_misc.h>
#include <asm/traps.h>
#include <asm/uaccess.h>

/*
 * The runtime support for deprecated instruction support can be in one of
 * following three states -
 *
 * 0 = undef
 * 1 = emulate (software emulation)
 * 2 = hw (supported in hardware)
 */
enum insn_emulation_mode {
	INSN_UNDEF,
	INSN_EMULATE,
	INSN_HW,
};

enum legacy_insn_status {
	INSN_DEPRECATED,
	INSN_OBSOLETE,
};

struct insn_emulation_ops {
	const char		*name;
	enum legacy_insn_status	status;
	struct undef_hook	*hooks;
	int			(*set_hw_mode)(bool enable);
};

struct insn_emulation {
	struct list_head node;
	struct insn_emulation_ops *ops;
	int current_mode;
	int min;
	int max;
};

static LIST_HEAD(insn_emulation);
static int nr_insn_emulated;
static DEFINE_RAW_SPINLOCK(insn_emulation_lock);

static void register_emulation_hooks(struct insn_emulation_ops *ops)
{
	struct undef_hook *hook;

	BUG_ON(!ops->hooks);

	for (hook = ops->hooks; hook->instr_mask; hook++)
		register_undef_hook(hook);

	pr_notice("Registered %s emulation handler\n", ops->name);
}

static void remove_emulation_hooks(struct insn_emulation_ops *ops)
{
	struct undef_hook *hook;

	BUG_ON(!ops->hooks);

	for (hook = ops->hooks; hook->instr_mask; hook++)
		unregister_undef_hook(hook);

	pr_notice("Removed %s emulation handler\n", ops->name);
}

static int update_insn_emulation_mode(struct insn_emulation *insn,
				       enum insn_emulation_mode prev)
{
	int ret = 0;

	switch (prev) {
	case INSN_UNDEF: /* Nothing to be done */
		break;
	case INSN_EMULATE:
		remove_emulation_hooks(insn->ops);
		break;
	case INSN_HW:
		if (insn->ops->set_hw_mode) {
			insn->ops->set_hw_mode(false);
			pr_notice("Disabled %s support\n", insn->ops->name);
		}
		break;
	}

	switch (insn->current_mode) {
	case INSN_UNDEF:
		break;
	case INSN_EMULATE:
		register_emulation_hooks(insn->ops);
		break;
	case INSN_HW:
		if (insn->ops->set_hw_mode && insn->ops->set_hw_mode(true))
			pr_notice("Enabled %s support\n", insn->ops->name);
		else
			ret = -EINVAL;
		break;
	}

	return ret;
}

static void register_insn_emulation(struct insn_emulation_ops *ops)
{
	unsigned long flags;
	struct insn_emulation *insn;

	insn = kzalloc(sizeof(*insn), GFP_KERNEL);
	insn->ops = ops;
	insn->min = INSN_UNDEF;

	switch (ops->status) {
	case INSN_DEPRECATED:
		insn->current_mode = INSN_EMULATE;
		insn->max = INSN_HW;
		break;
	case INSN_OBSOLETE:
		insn->current_mode = INSN_UNDEF;
		insn->max = INSN_EMULATE;
		break;
	}

	raw_spin_lock_irqsave(&insn_emulation_lock, flags);
	list_add(&insn->node, &insn_emulation);
	nr_insn_emulated++;
	raw_spin_unlock_irqrestore(&insn_emulation_lock, flags);

	/* Register any handlers if required */
	update_insn_emulation_mode(insn, INSN_UNDEF);
}

static int emulation_proc_handler(struct ctl_table *table, int write,
				  void __user *buffer, size_t *lenp,
				  loff_t *ppos)
{
	int ret = 0;
	struct insn_emulation *insn = (struct insn_emulation *) table->data;
	enum insn_emulation_mode prev_mode = insn->current_mode;

	table->data = &insn->current_mode;
	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);

	if (ret || !write || prev_mode == insn->current_mode)
		goto ret;

	ret = update_insn_emulation_mode(insn, prev_mode);
	if (!ret) {
		/* Mode change failed, revert to previous mode. */
		insn->current_mode = prev_mode;
		update_insn_emulation_mode(insn, INSN_UNDEF);
	}
ret:
	table->data = insn;
	return ret;
}

static struct ctl_table ctl_abi[] = {
	{
		.procname = "abi",
		.mode = 0555,
	},
	{ }
};

static void register_insn_emulation_sysctl(struct ctl_table *table)
{
	unsigned long flags;
	int i = 0;
	struct insn_emulation *insn;
	struct ctl_table *insns_sysctl, *sysctl;

	insns_sysctl = kzalloc(sizeof(*sysctl) * (nr_insn_emulated + 1),
			      GFP_KERNEL);

	raw_spin_lock_irqsave(&insn_emulation_lock, flags);
	list_for_each_entry(insn, &insn_emulation, node) {
		sysctl = &insns_sysctl[i];

		sysctl->mode = 0644;
		sysctl->maxlen = sizeof(int);

		sysctl->procname = insn->ops->name;
		sysctl->data = insn;
		sysctl->extra1 = &insn->min;
		sysctl->extra2 = &insn->max;
		sysctl->proc_handler = emulation_proc_handler;
		i++;
	}
	raw_spin_unlock_irqrestore(&insn_emulation_lock, flags);

	table->child = insns_sysctl;
	register_sysctl_table(table);
}

/*
 *  Implement emulation of the SWP/SWPB instructions using load-exclusive and
 *  store-exclusive.
 *
 *  Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>]
 *  Where: Rt  = destination
 *	   Rt2 = source
 *	   Rn  = address
 */

/*
 * Error-checking SWP macros implemented using ldxr{b}/stxr{b}
 */
#define __user_swpX_asm(data, addr, res, temp, B)		\
	__asm__ __volatile__(					\
	"	mov		%w2, %w1\n"			\
	"0:	ldxr"B"		%w1, [%3]\n"			\
	"1:	stxr"B"		%w0, %w2, [%3]\n"		\
	"	cbz		%w0, 2f\n"			\
	"	mov		%w0, %w4\n"			\
	"2:\n"							\
	"	.pushsection	 .fixup,\"ax\"\n"		\
	"	.align		2\n"				\
	"3:	mov		%w0, %w5\n"			\
	"	b		2b\n"				\
	"	.popsection"					\
	"	.pushsection	 __ex_table,\"a\"\n"		\
	"	.align		3\n"				\
	"	.quad		0b, 3b\n"			\
	"	.quad		1b, 3b\n"			\
	"	.popsection"					\
	: "=&r" (res), "+r" (data), "=&r" (temp)		\
	: "r" (addr), "i" (-EAGAIN), "i" (-EFAULT)		\
	: "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")

/*
 * Bit 22 of the instruction encoding distinguishes between
 * the SWP and SWPB variants (bit set means SWPB).
 */
#define TYPE_SWPB (1 << 22)

/*
 * Set up process info to signal segmentation fault - called on access error.
 */
static void set_segfault(struct pt_regs *regs, unsigned long addr)
{
	siginfo_t info;

	down_read(&current->mm->mmap_sem);
	if (find_vma(current->mm, addr) == NULL)
		info.si_code = SEGV_MAPERR;
	else
		info.si_code = SEGV_ACCERR;
	up_read(&current->mm->mmap_sem);

	info.si_signo = SIGSEGV;
	info.si_errno = 0;
	info.si_addr  = (void *) instruction_pointer(regs);

	pr_debug("SWP{B} emulation: access caused memory abort!\n");
	arm64_notify_die("Illegal memory access", regs, &info, 0);
}

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;

		if (type == TYPE_SWPB)
			__user_swpb_asm(*data, address, res, temp);
		else
			__user_swp_asm(*data, address, res, temp);

		if (likely(res != -EAGAIN) || signal_pending(current))
			break;

		cond_resched();
	}

	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, u32 instr)
{
	u32 destreg, data, type, address = 0;
	int rn, rt2, res = 0;

	perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->pc);

	type = instr & TYPE_SWPB;

	switch (arm_check_condition(instr, regs->pstate)) {
	case ARM_OPCODE_CONDTEST_PASS:
		break;
	case ARM_OPCODE_CONDTEST_FAIL:
		/* Condition failed - return to next instruction */
		goto ret;
	case ARM_OPCODE_CONDTEST_UNCOND:
		/* If unconditional encoding - not a SWP, undef */
		return -EFAULT;
	default:
		return -EINVAL;
	}

	rn = aarch32_insn_extract_reg_num(instr, A32_RN_OFFSET);
	rt2 = aarch32_insn_extract_reg_num(instr, A32_RT2_OFFSET);

	address = (u32)regs->user_regs.regs[rn];
	data	= (u32)regs->user_regs.regs[rt2];
	destreg = aarch32_insn_extract_reg_num(instr, A32_RT_OFFSET);

	pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
		rn, address, destreg,
		aarch32_insn_extract_reg_num(instr, A32_RT2_OFFSET), data);

	/* Check access in reasonable access range for both SWP and SWPB */
	if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
		pr_debug("SWP{B} emulation: access to 0x%08x not allowed!\n",
			address);
		goto fault;
	}

	res = emulate_swpX(address, &data, type);
	if (res == -EFAULT)
		goto fault;
	else if (res == 0)
		regs->user_regs.regs[destreg] = data;

ret:
	pr_warn_ratelimited("\"%s\" (%ld) uses obsolete SWP{B} instruction at 0x%llx\n",
			current->comm, (unsigned long)current->pid, regs->pc);

	regs->pc += 4;
	return 0;

fault:
	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.
 */
static struct undef_hook swp_hooks[] = {
	{
		.instr_mask	= 0x0fb00ff0,
		.instr_val	= 0x01000090,
		.pstate_mask	= COMPAT_PSR_MODE_MASK,
		.pstate_val	= COMPAT_PSR_MODE_USR,
		.fn		= swp_handler
	},
	{ }
};

static struct insn_emulation_ops swp_ops = {
	.name = "swp",
	.status = INSN_OBSOLETE,
	.hooks = swp_hooks,
	.set_hw_mode = NULL,
};

/*
 * Invoked as late_initcall, since not needed before init spawned.
 */
static int __init armv8_deprecated_init(void)
{
	if (IS_ENABLED(CONFIG_SWP_EMULATION))
		register_insn_emulation(&swp_ops);

	register_insn_emulation_sysctl(ctl_abi);

	return 0;
}

late_initcall(armv8_deprecated_init);