core.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * arch/arm/kernel/kprobes.c
 *
 * Kprobes on ARM
 *
 * Abhishek Sagar <sagar.abhishek@gmail.com>
 * Copyright (C) 2006, 2007 Motorola Inc.
 *
 * Nicolas Pitre <nico@marvell.com>
 * Copyright (C) 2007 Marvell Ltd.
 */

#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/stop_machine.h>
#include <linux/sched/debug.h>
#include <linux/stringify.h>
#include <asm/traps.h>
#include <asm/opcodes.h>
#include <asm/cacheflush.h>
#include <linux/percpu.h>
#include <linux/bug.h>
#include <asm/patch.h>
#include <asm/sections.h>

#include "../decode-arm.h"
#include "../decode-thumb.h"
#include "core.h"

#define MIN_STACK_SIZE(addr) 				\
	min((unsigned long)MAX_STACK_SIZE,		\
	    (unsigned long)current_thread_info() + THREAD_START_SP - (addr))

#define flush_insns(addr, size)				\
	flush_icache_range((unsigned long)(addr),	\
			   (unsigned long)(addr) +	\
			   (size))

DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);


int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
	kprobe_opcode_t insn;
	kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
	unsigned long addr = (unsigned long)p->addr;
	bool thumb;
	kprobe_decode_insn_t *decode_insn;
	const union decode_action *actions;
	int is;
	const struct decode_checker **checkers;

#ifdef CONFIG_THUMB2_KERNEL
	thumb = true;
	addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
	insn = __mem_to_opcode_thumb16(((u16 *)addr)[0]);
	if (is_wide_instruction(insn)) {
		u16 inst2 = __mem_to_opcode_thumb16(((u16 *)addr)[1]);
		insn = __opcode_thumb32_compose(insn, inst2);
		decode_insn = thumb32_probes_decode_insn;
		actions = kprobes_t32_actions;
		checkers = kprobes_t32_checkers;
	} else {
		decode_insn = thumb16_probes_decode_insn;
		actions = kprobes_t16_actions;
		checkers = kprobes_t16_checkers;
	}
#else /* !CONFIG_THUMB2_KERNEL */
	thumb = false;
	if (addr & 0x3)
		return -EINVAL;
	insn = __mem_to_opcode_arm(*p->addr);
	decode_insn = arm_probes_decode_insn;
	actions = kprobes_arm_actions;
	checkers = kprobes_arm_checkers;
#endif

	p->opcode = insn;
	p->ainsn.insn = tmp_insn;

	switch ((*decode_insn)(insn, &p->ainsn, true, actions, checkers)) {
	case INSN_REJECTED:	/* not supported */
		return -EINVAL;

	case INSN_GOOD:		/* instruction uses slot */
		p->ainsn.insn = get_insn_slot();
		if (!p->ainsn.insn)
			return -ENOMEM;
		for (is = 0; is < MAX_INSN_SIZE; ++is)
			p->ainsn.insn[is] = tmp_insn[is];
		flush_insns(p->ainsn.insn,
				sizeof(p->ainsn.insn[0]) * MAX_INSN_SIZE);
		p->ainsn.insn_fn = (probes_insn_fn_t *)
					((uintptr_t)p->ainsn.insn | thumb);
		break;

	case INSN_GOOD_NO_SLOT:	/* instruction doesn't need insn slot */
		p->ainsn.insn = NULL;
		break;
	}

	/*
	 * Never instrument insn like 'str r0, [sp, +/-r1]'. Also, insn likes
	 * 'str r0, [sp, #-68]' should also be prohibited.
	 * See __und_svc.
	 */
	if ((p->ainsn.stack_space < 0) ||
			(p->ainsn.stack_space > MAX_STACK_SIZE))
		return -EINVAL;

	return 0;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
	unsigned int brkp;
	void *addr;

	if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
		/* Remove any Thumb flag */
		addr = (void *)((uintptr_t)p->addr & ~1);

		if (is_wide_instruction(p->opcode))
			brkp = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION;
		else
			brkp = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION;
	} else {
		kprobe_opcode_t insn = p->opcode;

		addr = p->addr;
		brkp = KPROBE_ARM_BREAKPOINT_INSTRUCTION;

		if (insn >= 0xe0000000)
			brkp |= 0xe0000000;  /* Unconditional instruction */
		else
			brkp |= insn & 0xf0000000;  /* Copy condition from insn */
	}

	patch_text(addr, brkp);
}

/*
 * The actual disarming is done here on each CPU and synchronized using
 * stop_machine. This synchronization is necessary on SMP to avoid removing
 * a probe between the moment the 'Undefined Instruction' exception is raised
 * and the moment the exception handler reads the faulting instruction from
 * memory. It is also needed to atomically set the two half-words of a 32-bit
 * Thumb breakpoint.
 */
struct patch {
	void *addr;
	unsigned int insn;
};

static int __kprobes_remove_breakpoint(void *data)
{
	struct patch *p = data;
	__patch_text(p->addr, p->insn);
	return 0;
}

void __kprobes kprobes_remove_breakpoint(void *addr, unsigned int insn)
{
	struct patch p = {
		.addr = addr,
		.insn = insn,
	};
	stop_machine_cpuslocked(__kprobes_remove_breakpoint, &p,
				cpu_online_mask);
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
	kprobes_remove_breakpoint((void *)((uintptr_t)p->addr & ~1),
			p->opcode);
}

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
	if (p->ainsn.insn) {
		free_insn_slot(p->ainsn.insn, 0);
		p->ainsn.insn = NULL;
	}
}

static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
{
	kcb->prev_kprobe.kp = kprobe_running();
	kcb->prev_kprobe.status = kcb->kprobe_status;
}

static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
{
	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
	kcb->kprobe_status = kcb->prev_kprobe.status;
}

static void __kprobes set_current_kprobe(struct kprobe *p)
{
	__this_cpu_write(current_kprobe, p);
}

static void __kprobes
singlestep_skip(struct kprobe *p, struct pt_regs *regs)
{
#ifdef CONFIG_THUMB2_KERNEL
	regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
	if (is_wide_instruction(p->opcode))
		regs->ARM_pc += 4;
	else
		regs->ARM_pc += 2;
#else
	regs->ARM_pc += 4;
#endif
}

static inline void __kprobes
singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb)
{
	p->ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
}

/*
 * Called with IRQs disabled. IRQs must remain disabled from that point
 * all the way until processing this kprobe is complete.  The current
 * kprobes implementation cannot process more than one nested level of
 * kprobe, and that level is reserved for user kprobe handlers, so we can't
 * risk encountering a new kprobe in an interrupt handler.
 */
void __kprobes kprobe_handler(struct pt_regs *regs)
{
	struct kprobe *p, *cur;
	struct kprobe_ctlblk *kcb;

	kcb = get_kprobe_ctlblk();
	cur = kprobe_running();

#ifdef CONFIG_THUMB2_KERNEL
	/*
	 * First look for a probe which was registered using an address with
	 * bit 0 set, this is the usual situation for pointers to Thumb code.
	 * If not found, fallback to looking for one with bit 0 clear.
	 */
	p = get_kprobe((kprobe_opcode_t *)(regs->ARM_pc | 1));
	if (!p)
		p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);

#else /* ! CONFIG_THUMB2_KERNEL */
	p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
#endif

	if (p) {
		if (!p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
			/*
			 * Probe hit but conditional execution check failed,
			 * so just skip the instruction and continue as if
			 * nothing had happened.
			 * In this case, we can skip recursing check too.
			 */
			singlestep_skip(p, regs);
		} else if (cur) {
			/* Kprobe is pending, so we're recursing. */
			switch (kcb->kprobe_status) {
			case KPROBE_HIT_ACTIVE:
			case KPROBE_HIT_SSDONE:
			case KPROBE_HIT_SS:
				/* A pre- or post-handler probe got us here. */
				kprobes_inc_nmissed_count(p);
				save_previous_kprobe(kcb);
				set_current_kprobe(p);
				kcb->kprobe_status = KPROBE_REENTER;
				singlestep(p, regs, kcb);
				restore_previous_kprobe(kcb);
				break;
			case KPROBE_REENTER:
				/* A nested probe was hit in FIQ, it is a BUG */
				pr_warn("Unrecoverable kprobe detected.\n");
				dump_kprobe(p);
				fallthrough;
			default:
				/* impossible cases */
				BUG();
			}
		} else {
			/* Probe hit and conditional execution check ok. */
			set_current_kprobe(p);
			kcb->kprobe_status = KPROBE_HIT_ACTIVE;

			/*
			 * If we have no pre-handler or it returned 0, we
			 * continue with normal processing. If we have a
			 * pre-handler and it returned non-zero, it will
			 * modify the execution path and no need to single
			 * stepping. Let's just reset current kprobe and exit.
			 */
			if (!p->pre_handler || !p->pre_handler(p, regs)) {
				kcb->kprobe_status = KPROBE_HIT_SS;
				singlestep(p, regs, kcb);
				if (p->post_handler) {
					kcb->kprobe_status = KPROBE_HIT_SSDONE;
					p->post_handler(p, regs, 0);
				}
			}
			reset_current_kprobe();
		}
	} else {
		/*
		 * The probe was removed and a race is in progress.
		 * There is nothing we can do about it.  Let's restart
		 * the instruction.  By the time we can restart, the
		 * real instruction will be there.
		 */
	}
}

static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
{
	unsigned long flags;
	local_irq_save(flags);
	kprobe_handler(regs);
	local_irq_restore(flags);
	return 0;
}

int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
{
	struct kprobe *cur = kprobe_running();
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	switch (kcb->kprobe_status) {
	case KPROBE_HIT_SS:
	case KPROBE_REENTER:
		/*
		 * We are here because the instruction being single
		 * stepped caused a page fault. We reset the current
		 * kprobe and the PC to point back to the probe address
		 * and allow the page fault handler to continue as a
		 * normal page fault.
		 */
		regs->ARM_pc = (long)cur->addr;
		if (kcb->kprobe_status == KPROBE_REENTER) {
			restore_previous_kprobe(kcb);
		} else {
			reset_current_kprobe();
		}
		break;
	}

	return 0;
}

int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
				       unsigned long val, void *data)
{
	/*
	 * notify_die() is currently never called on ARM,
	 * so this callback is currently empty.
	 */
	return NOTIFY_DONE;
}

/*
 * When a retprobed function returns, trampoline_handler() is called,
 * calling the kretprobe's handler. We construct a struct pt_regs to
 * give a view of registers r0-r11 to the user return-handler.  This is
 * not a complete pt_regs structure, but that should be plenty sufficient
 * for kretprobe handlers which should normally be interested in r0 only
 * anyway.
 */
void __naked __kprobes kretprobe_trampoline(void)
{
	__asm__ __volatile__ (
		"stmdb	sp!, {r0 - r11}		\n\t"
		"mov	r0, sp			\n\t"
		"bl	trampoline_handler	\n\t"
		"mov	lr, r0			\n\t"
		"ldmia	sp!, {r0 - r11}		\n\t"
#ifdef CONFIG_THUMB2_KERNEL
		"bx	lr			\n\t"
#else
		"mov	pc, lr			\n\t"
#endif
		: : : "memory");
}

/* Called from kretprobe_trampoline */
static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
{
	return (void *)kretprobe_trampoline_handler(regs, &kretprobe_trampoline,
						    (void *)regs->ARM_fp);
}

void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
				      struct pt_regs *regs)
{
	ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
	ri->fp = (void *)regs->ARM_fp;

	/* Replace the return addr with trampoline addr. */
	regs->ARM_lr = (unsigned long)&kretprobe_trampoline;
}

int __kprobes arch_trampoline_kprobe(struct kprobe *p)
{
	return 0;
}

#ifdef CONFIG_THUMB2_KERNEL

static struct undef_hook kprobes_thumb16_break_hook = {
	.instr_mask	= 0xffff,
	.instr_val	= KPROBE_THUMB16_BREAKPOINT_INSTRUCTION,
	.cpsr_mask	= MODE_MASK,
	.cpsr_val	= SVC_MODE,
	.fn		= kprobe_trap_handler,
};

static struct undef_hook kprobes_thumb32_break_hook = {
	.instr_mask	= 0xffffffff,
	.instr_val	= KPROBE_THUMB32_BREAKPOINT_INSTRUCTION,
	.cpsr_mask	= MODE_MASK,
	.cpsr_val	= SVC_MODE,
	.fn		= kprobe_trap_handler,
};

#else  /* !CONFIG_THUMB2_KERNEL */

static struct undef_hook kprobes_arm_break_hook = {
	.instr_mask	= 0x0fffffff,
	.instr_val	= KPROBE_ARM_BREAKPOINT_INSTRUCTION,
	.cpsr_mask	= MODE_MASK,
	.cpsr_val	= SVC_MODE,
	.fn		= kprobe_trap_handler,
};

#endif /* !CONFIG_THUMB2_KERNEL */

int __init arch_init_kprobes()
{
	arm_probes_decode_init();
#ifdef CONFIG_THUMB2_KERNEL
	register_undef_hook(&kprobes_thumb16_break_hook);
	register_undef_hook(&kprobes_thumb32_break_hook);
#else
	register_undef_hook(&kprobes_arm_break_hook);
#endif
	return 0;
}

bool arch_within_kprobe_blacklist(unsigned long addr)
{
	void *a = (void *)addr;

	return __in_irqentry_text(addr) ||
	       in_entry_text(addr) ||
	       in_idmap_text(addr) ||
	       memory_contains(__kprobes_text_start, __kprobes_text_end, a, 1);
}