diff options
| -rw-r--r-- | arch/arm/kernel/kprobes-common.c | 258 | ||||
| -rw-r--r-- | arch/arm/kernel/kprobes.h | 248 |
2 files changed, 505 insertions, 1 deletions
diff --git a/arch/arm/kernel/kprobes-common.c b/arch/arm/kernel/kprobes-common.c index 87e91ce..1cb6a82 100644 --- a/arch/arm/kernel/kprobes-common.c +++ b/arch/arm/kernel/kprobes-common.c @@ -140,3 +140,261 @@ kprobe_check_cc * const kprobe_condition_checks[16] = { &__check_hi, &__check_ls, &__check_ge, &__check_lt, &__check_gt, &__check_le, &__check_al, &__check_al }; + + +/* + * Prepare an instruction slot to receive an instruction for emulating. + * This is done by placing a subroutine return after the location where the + * instruction will be placed. We also modify ARM instructions to be + * unconditional as the condition code will already be checked before any + * emulation handler is called. + */ +static kprobe_opcode_t __kprobes +prepare_emulated_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi, + bool thumb) +{ +#ifdef CONFIG_THUMB2_KERNEL + if (thumb) { + u16 *thumb_insn = (u16 *)asi->insn; + thumb_insn[1] = 0x4770; /* Thumb bx lr */ + thumb_insn[2] = 0x4770; /* Thumb bx lr */ + return insn; + } + asi->insn[1] = 0xe12fff1e; /* ARM bx lr */ +#else + asi->insn[1] = 0xe1a0f00e; /* mov pc, lr */ +#endif + /* Make an ARM instruction unconditional */ + if (insn < 0xe0000000) + insn = (insn | 0xe0000000) & ~0x10000000; + return insn; +} + +/* + * Write a (probably modified) instruction into the slot previously prepared by + * prepare_emulated_insn + */ +static void __kprobes +set_emulated_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi, + bool thumb) +{ +#ifdef CONFIG_THUMB2_KERNEL + if (thumb) { + u16 *ip = (u16 *)asi->insn; + if (is_wide_instruction(insn)) + *ip++ = insn >> 16; + *ip++ = insn; + return; + } +#endif + asi->insn[0] = insn; +} + +/* + * When we modify the register numbers encoded in an instruction to be emulated, + * the new values come from this define. For ARM and 32-bit Thumb instructions + * this gives... + * + * bit position 16 12 8 4 0 + * ---------------+---+---+---+---+---+ + * register r2 r0 r1 -- r3 + */ +#define INSN_NEW_BITS 0x00020103 + +/* Each nibble has same value as that at INSN_NEW_BITS bit 16 */ +#define INSN_SAMEAS16_BITS 0x22222222 + +/* + * Validate and modify each of the registers encoded in an instruction. + * + * Each nibble in regs contains a value from enum decode_reg_type. For each + * non-zero value, the corresponding nibble in pinsn is validated and modified + * according to the type. + */ +static bool __kprobes decode_regs(kprobe_opcode_t* pinsn, u32 regs) +{ + kprobe_opcode_t insn = *pinsn; + kprobe_opcode_t mask = 0xf; /* Start at least significant nibble */ + + for (; regs != 0; regs >>= 4, mask <<= 4) { + + kprobe_opcode_t new_bits = INSN_NEW_BITS; + + switch (regs & 0xf) { + + case REG_TYPE_NONE: + /* Nibble not a register, skip to next */ + continue; + + case REG_TYPE_ANY: + /* Any register is allowed */ + break; + + case REG_TYPE_SAMEAS16: + /* Replace register with same as at bit position 16 */ + new_bits = INSN_SAMEAS16_BITS; + break; + + case REG_TYPE_SP: + /* Only allow SP (R13) */ + if ((insn ^ 0xdddddddd) & mask) + goto reject; + break; + + case REG_TYPE_PC: + /* Only allow PC (R15) */ + if ((insn ^ 0xffffffff) & mask) + goto reject; + break; + + case REG_TYPE_NOSP: + /* Reject SP (R13) */ + if (((insn ^ 0xdddddddd) & mask) == 0) + goto reject; + break; + + case REG_TYPE_NOSPPC: + case REG_TYPE_NOSPPCX: + /* Reject SP and PC (R13 and R15) */ + if (((insn ^ 0xdddddddd) & 0xdddddddd & mask) == 0) + goto reject; + break; + + case REG_TYPE_NOPCWB: + if (!is_writeback(insn)) + break; /* No writeback, so any register is OK */ + /* fall through... */ + case REG_TYPE_NOPC: + case REG_TYPE_NOPCX: + /* Reject PC (R15) */ + if (((insn ^ 0xffffffff) & mask) == 0) + goto reject; + break; + } + + /* Replace value of nibble with new register number... */ + insn &= ~mask; + insn |= new_bits & mask; + } + + *pinsn = insn; + return true; + +reject: + return false; +} + +static const int decode_struct_sizes[NUM_DECODE_TYPES] = { + [DECODE_TYPE_TABLE] = sizeof(struct decode_table), + [DECODE_TYPE_CUSTOM] = sizeof(struct decode_custom), + [DECODE_TYPE_SIMULATE] = sizeof(struct decode_simulate), + [DECODE_TYPE_EMULATE] = sizeof(struct decode_emulate), + [DECODE_TYPE_OR] = sizeof(struct decode_or), + [DECODE_TYPE_REJECT] = sizeof(struct decode_reject) +}; + +/* + * kprobe_decode_insn operates on data tables in order to decode an ARM + * architecture instruction onto which a kprobe has been placed. + * + * These instruction decoding tables are a concatenation of entries each + * of which consist of one of the following structs: + * + * decode_table + * decode_custom + * decode_simulate + * decode_emulate + * decode_or + * decode_reject + * + * Each of these starts with a struct decode_header which has the following + * fields: + * + * type_regs + * mask + * value + * + * The least significant DECODE_TYPE_BITS of type_regs contains a value + * from enum decode_type, this indicates which of the decode_* structs + * the entry contains. The value DECODE_TYPE_END indicates the end of the + * table. + * + * When the table is parsed, each entry is checked in turn to see if it + * matches the instruction to be decoded using the test: + * + * (insn & mask) == value + * + * If no match is found before the end of the table is reached then decoding + * fails with INSN_REJECTED. + * + * When a match is found, decode_regs() is called to validate and modify each + * of the registers encoded in the instruction; the data it uses to do this + * is (type_regs >> DECODE_TYPE_BITS). A validation failure will cause decoding + * to fail with INSN_REJECTED. + * + * Once the instruction has passed the above tests, further processing + * depends on the type of the table entry's decode struct. + * + */ +int __kprobes +kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi, + const union decode_item *table, bool thumb) +{ + const struct decode_header *h = (struct decode_header *)table; + const struct decode_header *next; + bool matched = false; + + insn = prepare_emulated_insn(insn, asi, thumb); + + for (;; h = next) { + enum decode_type type = h->type_regs.bits & DECODE_TYPE_MASK; + u32 regs = h->type_regs.bits >> DECODE_TYPE_BITS; + + if (type == DECODE_TYPE_END) + return INSN_REJECTED; + + next = (struct decode_header *) + ((uintptr_t)h + decode_struct_sizes[type]); + + if (!matched && (insn & h->mask.bits) != h->value.bits) + continue; + + if (!decode_regs(&insn, regs)) + return INSN_REJECTED; + + switch (type) { + + case DECODE_TYPE_TABLE: { + struct decode_table *d = (struct decode_table *)h; + next = (struct decode_header *)d->table.table; + break; + } + + case DECODE_TYPE_CUSTOM: { + struct decode_custom *d = (struct decode_custom *)h; + return (*d->decoder.decoder)(insn, asi); + } + + case DECODE_TYPE_SIMULATE: { + struct decode_simulate *d = (struct decode_simulate *)h; + asi->insn_handler = d->handler.handler; + return INSN_GOOD_NO_SLOT; + } + + case DECODE_TYPE_EMULATE: { + struct decode_emulate *d = (struct decode_emulate *)h; + asi->insn_handler = d->handler.handler; + set_emulated_insn(insn, asi, thumb); + return INSN_GOOD; + } + + case DECODE_TYPE_OR: + matched = true; + break; + + case DECODE_TYPE_REJECT: + default: + return INSN_REJECTED; + } + } + } diff --git a/arch/arm/kernel/kprobes.h b/arch/arm/kernel/kprobes.h index e3803c6..c00681c 100644 --- a/arch/arm/kernel/kprobes.h +++ b/arch/arm/kernel/kprobes.h @@ -1,7 +1,9 @@ /* * arch/arm/kernel/kprobes.h * - * Contents moved from arch/arm/include/asm/kprobes.h which is + * Copyright (C) 2011 Jon Medhurst <tixy@yxit.co.uk>. + * + * 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 @@ -99,4 +101,248 @@ static inline unsigned long it_advance(unsigned long cpsr) */ #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) + + +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 */ |
