kprobes.h

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/*
 * arch/arm/kernel/kprobes.h
 *
 * Copyright (C) 2011 Jon Medhurst <[email protected]>.
 *
 * Some contents moved here from arch/arm/include/asm/kprobes.h which is
 * Copyright (C) 2006, 2007 Motorola Inc.
 *
 * 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.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 */

#ifndef _ARM_KERNEL_KPROBES_H
#define _ARM_KERNEL_KPROBES_H

/*
 * These undefined instructions must be unique and
 * reserved solely for kprobes' use.
 */
#define KPROBE_ARM_BREAKPOINT_INSTRUCTION   0x07f001f8
#define KPROBE_THUMB16_BREAKPOINT_INSTRUCTION   0xde18
#define KPROBE_THUMB32_BREAKPOINT_INSTRUCTION   0xf7f0a018


enum kprobe_insn {
    INSN_REJECTED,
    INSN_GOOD,
    INSN_GOOD_NO_SLOT
};

typedef enum kprobe_insn (kprobe_decode_insn_t)(kprobe_opcode_t,
                        struct arch_specific_insn *);

#ifdef CONFIG_THUMB2_KERNEL

enum kprobe_insn thumb16_kprobe_decode_insn(kprobe_opcode_t,
                        struct arch_specific_insn *);
enum kprobe_insn thumb32_kprobe_decode_insn(kprobe_opcode_t,
                        struct arch_specific_insn *);

#else /* !CONFIG_THUMB2_KERNEL */

enum kprobe_insn arm_kprobe_decode_insn(kprobe_opcode_t,
                    struct arch_specific_insn *);
#endif

void __init arm_kprobe_decode_init(void);

extern kprobe_check_cc * const kprobe_condition_checks[16];


#if __LINUX_ARM_ARCH__ >= 7

/* str_pc_offset is architecturally defined from ARMv7 onwards */
#define str_pc_offset 8
#define find_str_pc_offset()

#else /* __LINUX_ARM_ARCH__ < 7 */

/* We need a run-time check to determine str_pc_offset */
extern int str_pc_offset;
void __init find_str_pc_offset(void);

#endif


/*
 * Update ITSTATE after normal execution of an IT block instruction.
 *
 * The 8 IT state bits are split into two parts in CPSR:
 *  ITSTATE<1:0> are in CPSR<26:25>
 *  ITSTATE<7:2> are in CPSR<15:10>
 */
static inline unsigned long it_advance(unsigned long cpsr)
    {
    if ((cpsr & 0x06000400) == 0) {
        /* ITSTATE<2:0> == 0 means end of IT block, so clear IT state */
        cpsr &= ~PSR_IT_MASK;
    } else {
        /* We need to shift left ITSTATE<4:0> */
        const unsigned long mask = 0x06001c00;  /* Mask ITSTATE<4:0> */
        unsigned long it = cpsr & mask;
        it <<= 1;
        it |= it >> (27 - 10);  /* Carry ITSTATE<2> to correct place */
        it &= mask;
        cpsr &= ~mask;
        cpsr |= it;
    }
    return cpsr;
}

static inline void __kprobes bx_write_pc(long pcv, struct pt_regs *regs)
{
    long cpsr = regs->ARM_cpsr;
    if (pcv & 0x1) {
        cpsr |= PSR_T_BIT;
        pcv &= ~0x1;
    } else {
        cpsr &= ~PSR_T_BIT;
        pcv &= ~0x2;    /* Avoid UNPREDICTABLE address allignment */
    }
    regs->ARM_cpsr = cpsr;
    regs->ARM_pc = pcv;
}


#if __LINUX_ARM_ARCH__ >= 6

/* Kernels built for >= ARMv6 should never run on <= ARMv5 hardware, so... */
#define load_write_pc_interworks true
#define test_load_write_pc_interworking()

#else /* __LINUX_ARM_ARCH__ < 6 */

/* We need run-time testing to determine if load_write_pc() should interwork. */
extern bool load_write_pc_interworks;
void __init test_load_write_pc_interworking(void);

#endif

static inline void __kprobes load_write_pc(long pcv, struct pt_regs *regs)
{
    if (load_write_pc_interworks)
        bx_write_pc(pcv, regs);
    else
        regs->ARM_pc = pcv;
}


#if __LINUX_ARM_ARCH__ >= 7

#define alu_write_pc_interworks true
#define test_alu_write_pc_interworking()

#elif __LINUX_ARM_ARCH__ <= 5

/* Kernels built for <= ARMv5 should never run on >= ARMv6 hardware, so... */
#define alu_write_pc_interworks false
#define test_alu_write_pc_interworking()

#else /* __LINUX_ARM_ARCH__ == 6 */

/* We could be an ARMv6 binary on ARMv7 hardware so we need a run-time check. */
extern bool alu_write_pc_interworks;
void __init test_alu_write_pc_interworking(void);

#endif /* __LINUX_ARM_ARCH__ == 6 */

static inline void __kprobes alu_write_pc(long pcv, struct pt_regs *regs)
{
    if (alu_write_pc_interworks)
        bx_write_pc(pcv, regs);
    else
        regs->ARM_pc = pcv;
}


void __kprobes kprobe_simulate_nop(struct kprobe *p, struct pt_regs *regs);
void __kprobes kprobe_emulate_none(struct kprobe *p, struct pt_regs *regs);

enum kprobe_insn __kprobes
kprobe_decode_ldmstm(kprobe_opcode_t insn, struct arch_specific_insn *asi);

/*
 * Test if load/store instructions writeback the address register.
 * if P (bit 24) == 0 or W (bit 21) == 1
 */
#define is_writeback(insn) ((insn ^ 0x01000000) & 0x01200000)

/*
 * The following definitions and macros are used to build instruction
 * decoding tables for use by kprobe_decode_insn.
 *
 * These tables are a concatenation of entries each of which consist of one of
 * the decode_* structs. All of the fields in every type of decode structure
 * are of the union type decode_item, therefore the entire decode table can be
 * viewed as an array of these and declared like:
 *
 *  static const union decode_item table_name[] = {};
 *
 * In order to construct each entry in the table, macros are used to
 * initialise a number of sequential decode_item values in a layout which
 * matches the relevant struct. E.g. DECODE_SIMULATE initialise a struct
 * decode_simulate by initialising four decode_item objects like this...
 *
 *  {.bits = _type},
 *  {.bits = _mask},
 *  {.bits = _value},
 *  {.handler = _handler},
 *
 * Initialising a specified member of the union means that the compiler
 * will produce a warning if the argument is of an incorrect type.
 *
 * Below is a list of each of the macros used to initialise entries and a
 * description of the action performed when that entry is matched to an
 * instruction. A match is found when (instruction & mask) == value.
 *
 * DECODE_TABLE(mask, value, table)
 *  Instruction decoding jumps to parsing the new sub-table 'table'.
 *
 * DECODE_CUSTOM(mask, value, decoder)
 *  The custom function 'decoder' is called to the complete decoding
 *  of an instruction.
 *
 * DECODE_SIMULATE(mask, value, handler)
 *  Set the probes instruction handler to 'handler', this will be used
 *  to simulate the instruction when the probe is hit. Decoding returns
 *  with INSN_GOOD_NO_SLOT.
 *
 * DECODE_EMULATE(mask, value, handler)
 *  Set the probes instruction handler to 'handler', this will be used
 *  to emulate the instruction when the probe is hit. The modified
 *  instruction (see below) is placed in the probes instruction slot so it
 *  may be called by the emulation code. Decoding returns with INSN_GOOD.
 *
 * DECODE_REJECT(mask, value)
 *  Instruction decoding fails with INSN_REJECTED
 *
 * DECODE_OR(mask, value)
 *  This allows the mask/value test of multiple table entries to be
 *  logically ORed. Once an 'or' entry is matched the decoding action to
 *  be performed is that of the next entry which isn't an 'or'. E.g.
 *
 *      DECODE_OR   (mask1, value1)
 *      DECODE_OR   (mask2, value2)
 *      DECODE_SIMULATE (mask3, value3, simulation_handler)
 *
 *  This means that if any of the three mask/value pairs match the
 *  instruction being decoded, then 'simulation_handler' will be used
 *  for it.
 *
 * Both the SIMULATE and EMULATE macros have a second form which take an
 * additional 'regs' argument.
 *
 *  DECODE_SIMULATEX(mask, value, handler, regs)
 *  DECODE_EMULATEX (mask, value, handler, regs)
 *
 * These are used to specify what kind of CPU register is encoded in each of the
 * least significant 5 nibbles of the instruction being decoded. The regs value
 * is specified using the REGS macro, this takes any of the REG_TYPE_* values
 * from enum decode_reg_type as arguments; only the '*' part of the name is
 * given. E.g.
 *
 *  REGS(0, ANY, NOPC, 0, ANY)
 *
 * This indicates an instruction is encoded like:
 *
 *  bits 19..16 ignore
 *  bits 15..12 any register allowed here
 *  bits 11.. 8 any register except PC allowed here
 *  bits  7.. 4 ignore
 *  bits  3.. 0 any register allowed here
 *
 * This register specification is checked after a decode table entry is found to
 * match an instruction (through the mask/value test). Any invalid register then
 * found in the instruction will cause decoding to fail with INSN_REJECTED. In
 * the above example this would happen if bits 11..8 of the instruction were
 * 1111, indicating R15 or PC.
 *
 * As well as checking for legal combinations of registers, this data is also
 * used to modify the registers encoded in the instructions so that an
 * emulation routines can use it. (See decode_regs() and INSN_NEW_BITS.)
 *
 * Here is a real example which matches ARM instructions of the form
 * "AND <Rd>,<Rn>,<Rm>,<shift> <Rs>"
 *
 *  DECODE_EMULATEX (0x0e000090, 0x00000010, emulate_rd12rn16rm0rs8_rwflags,
 *                       REGS(ANY, ANY, NOPC, 0, ANY)),
 *                            ^    ^    ^        ^
 *                            Rn   Rd   Rs       Rm
 *
 * Decoding the instruction "AND R4, R5, R6, ASL R15" will be rejected because
 * Rs == R15
 *
 * Decoding the instruction "AND R4, R5, R6, ASL R7" will be accepted and the
 * instruction will be modified to "AND R0, R2, R3, ASL R1" and then placed into
 * the kprobes instruction slot. This can then be called later by the handler
 * function emulate_rd12rn16rm0rs8_rwflags in order to simulate the instruction.
 */

enum decode_type {
    DECODE_TYPE_END,
    DECODE_TYPE_TABLE,
    DECODE_TYPE_CUSTOM,
    DECODE_TYPE_SIMULATE,
    DECODE_TYPE_EMULATE,
    DECODE_TYPE_OR,
    DECODE_TYPE_REJECT,
    NUM_DECODE_TYPES /* Must be last enum */
};

#define DECODE_TYPE_BITS    4
#define DECODE_TYPE_MASK    ((1 << DECODE_TYPE_BITS) - 1)

enum decode_reg_type {
    REG_TYPE_NONE = 0, /* Not a register, ignore */
    REG_TYPE_ANY,      /* Any register allowed */
    REG_TYPE_SAMEAS16, /* Register should be same as that at bits 19..16 */
    REG_TYPE_SP,       /* Register must be SP */
    REG_TYPE_PC,       /* Register must be PC */
    REG_TYPE_NOSP,     /* Register must not be SP */
    REG_TYPE_NOSPPC,   /* Register must not be SP or PC */
    REG_TYPE_NOPC,     /* Register must not be PC */
    REG_TYPE_NOPCWB,   /* No PC if load/store write-back flag also set */

    /* The following types are used when the encoding for PC indicates
     * another instruction form. This distiction only matters for test
     * case coverage checks.
     */
    REG_TYPE_NOPCX,    /* Register must not be PC */
    REG_TYPE_NOSPPCX,  /* Register must not be SP or PC */

    /* Alias to allow '0' arg to be used in REGS macro. */
    REG_TYPE_0 = REG_TYPE_NONE
};

#define REGS(r16, r12, r8, r4, r0)  \
    ((REG_TYPE_##r16) << 16) +  \
    ((REG_TYPE_##r12) << 12) +  \
    ((REG_TYPE_##r8) << 8) +    \
    ((REG_TYPE_##r4) << 4) +    \
    (REG_TYPE_##r0)

union decode_item {
    u32         bits;
    const union decode_item *table;
    kprobe_insn_handler_t   *handler;
    kprobe_decode_insn_t    *decoder;
};


#define DECODE_END          \
    {.bits = DECODE_TYPE_END}


struct decode_header {
    union decode_item   type_regs;
    union decode_item   mask;
    union decode_item   value;
};

#define DECODE_HEADER(_type, _mask, _value, _regs)      \
    {.bits = (_type) | ((_regs) << DECODE_TYPE_BITS)},  \
    {.bits = (_mask)},                  \
    {.bits = (_value)}


struct decode_table {
    struct decode_header    header;
    union decode_item   table;
};

#define DECODE_TABLE(_mask, _value, _table)         \
    DECODE_HEADER(DECODE_TYPE_TABLE, _mask, _value, 0), \
    {.table = (_table)}


struct decode_custom {
    struct decode_header    header;
    union decode_item   decoder;
};

#define DECODE_CUSTOM(_mask, _value, _decoder)          \
    DECODE_HEADER(DECODE_TYPE_CUSTOM, _mask, _value, 0),    \
    {.decoder = (_decoder)}


struct decode_simulate {
    struct decode_header    header;
    union decode_item   handler;
};

#define DECODE_SIMULATEX(_mask, _value, _handler, _regs)        \
    DECODE_HEADER(DECODE_TYPE_SIMULATE, _mask, _value, _regs),  \
    {.handler = (_handler)}

#define DECODE_SIMULATE(_mask, _value, _handler)    \
    DECODE_SIMULATEX(_mask, _value, _handler, 0)


struct decode_emulate {
    struct decode_header    header;
    union decode_item   handler;
};

#define DECODE_EMULATEX(_mask, _value, _handler, _regs)         \
    DECODE_HEADER(DECODE_TYPE_EMULATE, _mask, _value, _regs),   \
    {.handler = (_handler)}

#define DECODE_EMULATE(_mask, _value, _handler)     \
    DECODE_EMULATEX(_mask, _value, _handler, 0)


struct decode_or {
    struct decode_header    header;
};

#define DECODE_OR(_mask, _value)                \
    DECODE_HEADER(DECODE_TYPE_OR, _mask, _value, 0)


struct decode_reject {
    struct decode_header    header;
};

#define DECODE_REJECT(_mask, _value)                \
    DECODE_HEADER(DECODE_TYPE_REJECT, _mask, _value, 0)


#ifdef CONFIG_THUMB2_KERNEL
extern const union decode_item kprobe_decode_thumb16_table[];
extern const union decode_item kprobe_decode_thumb32_table[];
#else
extern const union decode_item kprobe_decode_arm_table[];
#endif


int kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi,
            const union decode_item *table, bool thumb16);


#endif /* _ARM_KERNEL_KPROBES_H */