linux/arch/arm/kernel/uprobes-arm.c

/*
 * Copyright (C) 2012 Rabin Vincent <rabin at rab.in>
 *
 * 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/kernel.h>
#include <linux/types.h>
#include <linux/stddef.h>
#include <linux/wait.h>
#include <linux/uprobes.h>
#include <linux/module.h>

#include "probes.h"
#include "probes-arm.h"
#include "uprobes.h"

static int uprobes_substitute_pc(unsigned long *pinsn, u32 oregs)
{
	probes_opcode_t insn = __mem_to_opcode_arm(*pinsn);
	probes_opcode_t temp;
	probes_opcode_t mask;
	int freereg;
	u32 free = 0xffff;
	u32 regs;

	for (regs = oregs; regs; regs >>= 4, insn >>= 4) {
		if ((regs & 0xf) == REG_TYPE_NONE)
			continue;

		free &= ~(1 << (insn & 0xf));
	}

	/* No PC, no problem */
	if (free & (1 << 15))
		return 15;

	if (!free)
		return -1;

	/*
	 * fls instead of ffs ensures that for "ldrd r0, r1, [pc]" we would
	 * pick LR instead of R1.
	 */
	freereg = free = fls(free) - 1;

	temp = __mem_to_opcode_arm(*pinsn);
	insn = temp;
	regs = oregs;
	mask = 0xf;

	for (; regs; regs >>= 4, mask <<= 4, free <<= 4, temp >>= 4) {
		if ((regs & 0xf) == REG_TYPE_NONE)
			continue;

		if ((temp & 0xf) != 15)
			continue;

		insn &= ~mask;
		insn |= free & mask;
	}

	*pinsn = __opcode_to_mem_arm(insn);
	return freereg;
}

static void uprobe_set_pc(struct arch_uprobe *auprobe,
			  struct arch_uprobe_task *autask,
			  struct pt_regs *regs)
{
	u32 pcreg = auprobe->pcreg;

	autask->backup = regs->uregs[pcreg];
	regs->uregs[pcreg] = regs->ARM_pc + 8;
}

static void uprobe_unset_pc(struct arch_uprobe *auprobe,
			    struct arch_uprobe_task *autask,
			    struct pt_regs *regs)
{
	/* PC will be taken care of by common code */
	regs->uregs[auprobe->pcreg] = autask->backup;
}

static void uprobe_aluwrite_pc(struct arch_uprobe *auprobe,
			       struct arch_uprobe_task *autask,
			       struct pt_regs *regs)
{
	u32 pcreg = auprobe->pcreg;

	alu_write_pc(regs->uregs[pcreg], regs);
	regs->uregs[pcreg] = autask->backup;
}

static void uprobe_write_pc(struct arch_uprobe *auprobe,
			    struct arch_uprobe_task *autask,
			    struct pt_regs *regs)
{
	u32 pcreg = auprobe->pcreg;

	load_write_pc(regs->uregs[pcreg], regs);
	regs->uregs[pcreg] = autask->backup;
}

enum probes_insn
decode_pc_ro(probes_opcode_t insn, struct arch_probes_insn *asi,
	     const struct decode_header *d)
{
	struct arch_uprobe *auprobe = container_of(asi, struct arch_uprobe,
						   asi);
	struct decode_emulate *decode = (struct decode_emulate *) d;
	u32 regs = decode->header.type_regs.bits >> DECODE_TYPE_BITS;
	int reg;

	reg = uprobes_substitute_pc(&auprobe->ixol[0], regs);
	if (reg == 15)
		return INSN_GOOD;

	if (reg == -1)
		return INSN_REJECTED;

	auprobe->pcreg = reg;
	auprobe->prehandler = uprobe_set_pc;
	auprobe->posthandler = uprobe_unset_pc;

	return INSN_GOOD;
}

enum probes_insn
decode_wb_pc(probes_opcode_t insn, struct arch_probes_insn *asi,
	     const struct decode_header *d, bool alu)
{
	struct arch_uprobe *auprobe = container_of(asi, struct arch_uprobe,
						   asi);
	enum probes_insn ret = decode_pc_ro(insn, asi, d);

	if (((insn >> 12) & 0xf) == 15)
		auprobe->posthandler = alu ? uprobe_aluwrite_pc
					   : uprobe_write_pc;

	return ret;
}

enum probes_insn
decode_rd12rn16rm0rs8_rwflags(probes_opcode_t insn,
			      struct arch_probes_insn *asi,
			      const struct decode_header *d)
{
	return decode_wb_pc(insn, asi, d, true);
}

enum probes_insn
decode_ldr(probes_opcode_t insn, struct arch_probes_insn *asi,
	   const struct decode_header *d)
{
	return decode_wb_pc(insn, asi, d, false);
}

enum probes_insn
uprobe_decode_ldmstm(probes_opcode_t insn,
		     struct arch_probes_insn *asi,
		     const struct decode_header *d)
{
	struct arch_uprobe *auprobe = container_of(asi, struct arch_uprobe,
						   asi);
	unsigned reglist = insn & 0xffff;
	int rn = (insn >> 16) & 0xf;
	int lbit = insn & (1 << 20);
	unsigned used = reglist | (1 << rn);

	if (rn == 15)
		return INSN_REJECTED;

	if (!(used & (1 << 15)))
		return INSN_GOOD;

	if (used & (1 << 14))
		return INSN_REJECTED;

	/* Use LR instead of PC */
	insn ^= 0xc000;

	auprobe->pcreg = 14;
	auprobe->ixol[0] = __opcode_to_mem_arm(insn);

	auprobe->prehandler = uprobe_set_pc;
	if (lbit)
		auprobe->posthandler = uprobe_write_pc;
	else
		auprobe->posthandler = uprobe_unset_pc;

	return INSN_GOOD;
}

const union decode_action uprobes_probes_actions[] = {
	[PROBES_EMULATE_NONE] = {.handler = probes_simulate_nop},
	[PROBES_SIMULATE_NOP] = {.handler = probes_simulate_nop},
	[PROBES_PRELOAD_IMM] = {.handler = probes_simulate_nop},
	[PROBES_PRELOAD_REG] = {.handler = probes_simulate_nop},
	[PROBES_BRANCH_IMM] = {.handler = simulate_blx1},
	[PROBES_MRS] = {.handler = simulate_mrs},
	[PROBES_BRANCH_REG] = {.handler = simulate_blx2bx},
	[PROBES_CLZ] = {.handler = probes_simulate_nop},
	[PROBES_SATURATING_ARITHMETIC] = {.handler = probes_simulate_nop},
	[PROBES_MUL1] = {.handler = probes_simulate_nop},
	[PROBES_MUL2] = {.handler = probes_simulate_nop},
	[PROBES_SWP] = {.handler = probes_simulate_nop},
	[PROBES_LDRSTRD] = {.decoder = decode_pc_ro},
	[PROBES_LOAD_EXTRA] = {.decoder = decode_pc_ro},
	[PROBES_LOAD] = {.decoder = decode_ldr},
	[PROBES_STORE_EXTRA] = {.decoder = decode_pc_ro},
	[PROBES_STORE] = {.decoder = decode_pc_ro},
	[PROBES_MOV_IP_SP] = {.handler = simulate_mov_ipsp},
	[PROBES_DATA_PROCESSING_REG] = {
		.decoder = decode_rd12rn16rm0rs8_rwflags},
	[PROBES_DATA_PROCESSING_IMM] = {
		.decoder = decode_rd12rn16rm0rs8_rwflags},
	[PROBES_MOV_HALFWORD] = {.handler = probes_simulate_nop},
	[PROBES_SEV] = {.handler = probes_simulate_nop},
	[PROBES_WFE] = {.handler = probes_simulate_nop},
	[PROBES_SATURATE] = {.handler = probes_simulate_nop},
	[PROBES_REV] = {.handler = probes_simulate_nop},
	[PROBES_MMI] = {.handler = probes_simulate_nop},
	[PROBES_PACK] = {.handler = probes_simulate_nop},
	[PROBES_EXTEND] = {.handler = probes_simulate_nop},
	[PROBES_EXTEND_ADD] = {.handler = probes_simulate_nop},
	[PROBES_MUL_ADD_LONG] = {.handler = probes_simulate_nop},
	[PROBES_MUL_ADD] = {.handler = probes_simulate_nop},
	[PROBES_BITFIELD] = {.handler = probes_simulate_nop},
	[PROBES_BRANCH] = {.handler = simulate_bbl},
	[PROBES_LDMSTM] = {.decoder = uprobe_decode_ldmstm}
};