linux/arch/arm64/kernel/armv8_deprecated.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  Copyright (C) 2014 ARM Limited
 */

#include <linux/cpu.h>
#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 <linux/uaccess.h>

#include <asm/cpufeature.h>
#include <asm/insn.h>
#include <asm/sysreg.h>
#include <asm/system_misc.h>
#include <asm/traps.h>

#define CREATE_TRACE_POINTS
#include "trace-events-emulation.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,
	INSN_UNAVAILABLE,
};

struct insn_emulation {
	const char			*name;
	enum legacy_insn_status		status;
	bool				(*try_emulate)(struct pt_regs *regs,
						       u32 insn);
	int				(*set_hw_mode)(bool enable);

	int current_mode;
	int min;
	int max;

	/*
	 * sysctl for this emulation + a sentinal entry.
	 */
	struct ctl_table sysctl[2];
};

#define ARM_OPCODE_CONDTEST_FAIL   0
#define ARM_OPCODE_CONDTEST_PASS   1
#define ARM_OPCODE_CONDTEST_UNCOND 2

#define	ARM_OPCODE_CONDITION_UNCOND	0xf

static unsigned int __maybe_unused aarch32_check_condition(u32 opcode, u32 psr)
{
	u32 cc_bits  = opcode >> 28;

	if (cc_bits != ARM_OPCODE_CONDITION_UNCOND) {
		if ((*aarch32_opcode_cond_checks[cc_bits])(psr))
			return ARM_OPCODE_CONDTEST_PASS;
		else
			return ARM_OPCODE_CONDTEST_FAIL;
	}
	return ARM_OPCODE_CONDTEST_UNCOND;
}

#ifdef CONFIG_SWP_EMULATION
/*
 *  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}
 */

/* Arbitrary constant to ensure forward-progress of the LL/SC loop */
#define __SWP_LL_SC_LOOPS	4

#define __user_swpX_asm(data, addr, res, temp, temp2, B)	\
do {								\
	uaccess_enable_privileged();				\
	__asm__ __volatile__(					\
	"	mov		%w3, %w6\n"			\
	"0:	ldxr"B"		%w2, [%4]\n"			\
	"1:	stxr"B"		%w0, %w1, [%4]\n"		\
	"	cbz		%w0, 2f\n"			\
	"	sub		%w3, %w3, #1\n"			\
	"	cbnz		%w3, 0b\n"			\
	"	mov		%w0, %w5\n"			\
	"	b		3f\n"				\
	"2:\n"							\
	"	mov		%w1, %w2\n"			\
	"3:\n"							\
	_ASM_EXTABLE_UACCESS_ERR(0b, 3b, %w0)			\
	_ASM_EXTABLE_UACCESS_ERR(1b, 3b, %w0)			\
	: "=&r" (res), "+r" (data), "=&r" (temp), "=&r" (temp2)	\
	: "r" ((unsigned long)addr), "i" (-EAGAIN),		\
	  "i" (__SWP_LL_SC_LOOPS)				\
	: "memory");						\
	uaccess_disable_privileged();				\
} while (0)

#define __user_swp_asm(data, addr, res, temp, temp2) \
	__user_swpX_asm(data, addr, res, temp, temp2, "")
#define __user_swpb_asm(data, addr, res, temp, temp2) \
	__user_swpX_asm(data, addr, res, temp, temp2, "b")

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

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, temp2;

		if (type == TYPE_SWPB)
			__user_swpb_asm(*data, address, res, temp, temp2);
		else
			__user_swp_asm(*data, address, res, temp, temp2);

		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;
	const void __user *user_ptr;
	int rn, rt2, res = 0;

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

	type = instr & TYPE_SWPB;

	switch (aarch32_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 */
	user_ptr = (const void __user *)(unsigned long)(address & ~3);
	if (!access_ok(user_ptr, 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:
	if (type == TYPE_SWPB)
		trace_instruction_emulation("swpb", regs->pc);
	else
		trace_instruction_emulation("swp", regs->pc);

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

	arm64_skip_faulting_instruction(regs, 4);
	return 0;

fault:
	pr_debug("SWP{B} emulation: access caused memory abort!\n");
	arm64_notify_segfault(address);

	return 0;
}

static bool try_emulate_swp(struct pt_regs *regs, u32 insn)
{
	/* SWP{B} only exists in ARM state and does not exist in Thumb */
	if (!compat_user_mode(regs) || compat_thumb_mode(regs))
		return false;

	if ((insn & 0x0fb00ff0) != 0x01000090)
		return false;

	return swp_handler(regs, insn) == 0;
}

static struct insn_emulation insn_swp = {
	.name = "swp",
	.status = INSN_OBSOLETE,
	.try_emulate = try_emulate_swp,
	.set_hw_mode = NULL,
};
#endif /* CONFIG_SWP_EMULATION */

#ifdef CONFIG_CP15_BARRIER_EMULATION
static int cp15barrier_handler(struct pt_regs *regs, u32 instr)
{
	perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->pc);

	switch (aarch32_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 barrier instruction */
		return -EFAULT;
	default:
		return -EINVAL;
	}

	switch (aarch32_insn_mcr_extract_crm(instr)) {
	case 10:
		/*
		 * dmb - mcr p15, 0, Rt, c7, c10, 5
		 * dsb - mcr p15, 0, Rt, c7, c10, 4
		 */
		if (aarch32_insn_mcr_extract_opc2(instr) == 5) {
			dmb(sy);
			trace_instruction_emulation(
				"mcr p15, 0, Rt, c7, c10, 5 ; dmb", regs->pc);
		} else {
			dsb(sy);
			trace_instruction_emulation(
				"mcr p15, 0, Rt, c7, c10, 4 ; dsb", regs->pc);
		}
		break;
	case 5:
		/*
		 * isb - mcr p15, 0, Rt, c7, c5, 4
		 *
		 * Taking an exception or returning from one acts as an
		 * instruction barrier. So no explicit barrier needed here.
		 */
		trace_instruction_emulation(
			"mcr p15, 0, Rt, c7, c5, 4 ; isb", regs->pc);
		break;
	}

ret:
	pr_warn_ratelimited("\"%s\" (%ld) uses deprecated CP15 Barrier instruction at 0x%llx\n",
			current->comm, (unsigned long)current->pid, regs->pc);

	arm64_skip_faulting_instruction(regs, 4);
	return 0;
}

static int cp15_barrier_set_hw_mode(bool enable)
{
	if (enable)
		sysreg_clear_set(sctlr_el1, 0, SCTLR_EL1_CP15BEN);
	else
		sysreg_clear_set(sctlr_el1, SCTLR_EL1_CP15BEN, 0);
	return 0;
}

static bool try_emulate_cp15_barrier(struct pt_regs *regs, u32 insn)
{
	if (!compat_user_mode(regs) || compat_thumb_mode(regs))
		return false;

	if ((insn & 0x0fff0fdf) == 0x0e070f9a)
		return cp15barrier_handler(regs, insn) == 0;

	if ((insn & 0x0fff0fff) == 0x0e070f95)
		return cp15barrier_handler(regs, insn) == 0;

	return false;
}

static struct insn_emulation insn_cp15_barrier = {
	.name = "cp15_barrier",
	.status = INSN_DEPRECATED,
	.try_emulate = try_emulate_cp15_barrier,
	.set_hw_mode = cp15_barrier_set_hw_mode,
};
#endif /* CONFIG_CP15_BARRIER_EMULATION */

#ifdef CONFIG_SETEND_EMULATION
static int setend_set_hw_mode(bool enable)
{
	if (!cpu_supports_mixed_endian_el0())
		return -EINVAL;

	if (enable)
		sysreg_clear_set(sctlr_el1, SCTLR_EL1_SED, 0);
	else
		sysreg_clear_set(sctlr_el1, 0, SCTLR_EL1_SED);
	return 0;
}

static int compat_setend_handler(struct pt_regs *regs, u32 big_endian)
{
	char *insn;

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

	if (big_endian) {
		insn = "setend be";
		regs->pstate |= PSR_AA32_E_BIT;
	} else {
		insn = "setend le";
		regs->pstate &= ~PSR_AA32_E_BIT;
	}

	trace_instruction_emulation(insn, regs->pc);
	pr_warn_ratelimited("\"%s\" (%ld) uses deprecated setend instruction at 0x%llx\n",
			current->comm, (unsigned long)current->pid, regs->pc);

	return 0;
}

static int a32_setend_handler(struct pt_regs *regs, u32 instr)
{
	int rc = compat_setend_handler(regs, (instr >> 9) & 1);
	arm64_skip_faulting_instruction(regs, 4);
	return rc;
}

static int t16_setend_handler(struct pt_regs *regs, u32 instr)
{
	int rc = compat_setend_handler(regs, (instr >> 3) & 1);
	arm64_skip_faulting_instruction(regs, 2);
	return rc;
}

static bool try_emulate_setend(struct pt_regs *regs, u32 insn)
{
	if (compat_thumb_mode(regs) &&
	    (insn & 0xfffffff7) == 0x0000b650)
		return t16_setend_handler(regs, insn) == 0;

	if (compat_user_mode(regs) &&
	    (insn & 0xfffffdff) == 0xf1010000)
		return a32_setend_handler(regs, insn) == 0;

	return false;
}

static struct insn_emulation insn_setend = {
	.name = "setend",
	.status = INSN_DEPRECATED,
	.try_emulate = try_emulate_setend,
	.set_hw_mode = setend_set_hw_mode,
};
#endif /* CONFIG_SETEND_EMULATION */

static struct insn_emulation *insn_emulations[] = {
#ifdef CONFIG_SWP_EMULATION
	&insn_swp,
#endif
#ifdef CONFIG_CP15_BARRIER_EMULATION
	&insn_cp15_barrier,
#endif
#ifdef CONFIG_SETEND_EMULATION
	&insn_setend,
#endif
};

static DEFINE_MUTEX(insn_emulation_mutex);

static void enable_insn_hw_mode(void *data)
{
	struct insn_emulation *insn = data;
	if (insn->set_hw_mode)
		insn->set_hw_mode(true);
}

static void disable_insn_hw_mode(void *data)
{
	struct insn_emulation *insn = data;
	if (insn->set_hw_mode)
		insn->set_hw_mode(false);
}

/* Run set_hw_mode(mode) on all active CPUs */
static int run_all_cpu_set_hw_mode(struct insn_emulation *insn, bool enable)
{
	if (!insn->set_hw_mode)
		return -EINVAL;
	if (enable)
		on_each_cpu(enable_insn_hw_mode, (void *)insn, true);
	else
		on_each_cpu(disable_insn_hw_mode, (void *)insn, true);
	return 0;
}

/*
 * Run set_hw_mode for all insns on a starting CPU.
 * Returns:
 *  0 		- If all the hooks ran successfully.
 * -EINVAL	- At least one hook is not supported by the CPU.
 */
static int run_all_insn_set_hw_mode(unsigned int cpu)
{
	int rc = 0;
	unsigned long flags;

	/*
	 * Disable IRQs to serialize against an IPI from
	 * run_all_cpu_set_hw_mode(), ensuring the HW is programmed to the most
	 * recent enablement state if the two race with one another.
	 */
	local_irq_save(flags);
	for (int i = 0; i < ARRAY_SIZE(insn_emulations); i++) {
		struct insn_emulation *insn = insn_emulations[i];
		bool enable = READ_ONCE(insn->current_mode) == INSN_HW;
		if (insn->set_hw_mode && insn->set_hw_mode(enable)) {
			pr_warn("CPU[%u] cannot support the emulation of %s",
				cpu, insn->name);
			rc = -EINVAL;
		}
	}
	local_irq_restore(flags);

	return rc;
}

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:
		break;
	case INSN_HW:
		if (!run_all_cpu_set_hw_mode(insn, false))
			pr_notice("Disabled %s support\n", insn->name);
		break;
	}

	switch (insn->current_mode) {
	case INSN_UNDEF:
		break;
	case INSN_EMULATE:
		break;
	case INSN_HW:
		ret = run_all_cpu_set_hw_mode(insn, true);
		if (!ret)
			pr_notice("Enabled %s support\n", insn->name);
		break;
	}

	return ret;
}

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

	mutex_lock(&insn_emulation_mutex);
	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. */
		WRITE_ONCE(insn->current_mode, prev_mode);
		update_insn_emulation_mode(insn, INSN_UNDEF);
	}
ret:
	mutex_unlock(&insn_emulation_mutex);
	return ret;
}

static void __init register_insn_emulation(struct insn_emulation *insn)
{
	struct ctl_table *sysctl;

	insn->min = INSN_UNDEF;

	switch (insn->status) {
	case INSN_DEPRECATED:
		insn->current_mode = INSN_EMULATE;
		/* Disable the HW mode if it was turned on at early boot time */
		run_all_cpu_set_hw_mode(insn, false);
		insn->max = INSN_HW;
		break;
	case INSN_OBSOLETE:
		insn->current_mode = INSN_UNDEF;
		insn->max = INSN_EMULATE;
		break;
	case INSN_UNAVAILABLE:
		insn->current_mode = INSN_UNDEF;
		insn->max = INSN_UNDEF;
		break;
	}

	/* Program the HW if required */
	update_insn_emulation_mode(insn, INSN_UNDEF);

	if (insn->status != INSN_UNAVAILABLE) {
		sysctl = &insn->sysctl[0];

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

		sysctl->procname = insn->name;
		sysctl->data = &insn->current_mode;
		sysctl->extra1 = &insn->min;
		sysctl->extra2 = &insn->max;
		sysctl->proc_handler = emulation_proc_handler;

		register_sysctl_sz("abi", sysctl, 1);
	}
}

bool try_emulate_armv8_deprecated(struct pt_regs *regs, u32 insn)
{
	for (int i = 0; i < ARRAY_SIZE(insn_emulations); i++) {
		struct insn_emulation *ie = insn_emulations[i];

		if (ie->status == INSN_UNAVAILABLE)
			continue;

		/*
		 * A trap may race with the mode being changed
		 * INSN_EMULATE<->INSN_HW. Try to emulate the instruction to
		 * avoid a spurious UNDEF.
		 */
		if (READ_ONCE(ie->current_mode) == INSN_UNDEF)
			continue;

		if (ie->try_emulate(regs, insn))
			return true;
	}

	return false;
}

/*
 * Invoked as core_initcall, which guarantees that the instruction
 * emulation is ready for userspace.
 */
static int __init armv8_deprecated_init(void)
{
#ifdef CONFIG_SETEND_EMULATION
	if (!system_supports_mixed_endian_el0()) {
		insn_setend.status = INSN_UNAVAILABLE;
		pr_info("setend instruction emulation is not supported on this system\n");
	}

#endif
	for (int i = 0; i < ARRAY_SIZE(insn_emulations); i++) {
		struct insn_emulation *ie = insn_emulations[i];

		if (ie->status == INSN_UNAVAILABLE)
			continue;

		register_insn_emulation(ie);
	}

	cpuhp_setup_state_nocalls(CPUHP_AP_ARM64_ISNDEP_STARTING,
				  "arm64/isndep:starting",
				  run_all_insn_set_hw_mode, NULL);
	return 0;
}

core_initcall(armv8_deprecated_init);