/*
* arch/arm/kernel/kprobes-common.c
*
* Copyright (C) 2011 Jon Medhurst <tixy@yxit.co.uk>.
*
* Some contents moved here from arch/arm/include/asm/kprobes-arm.c 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.
*/
#include <linux/kernel.h>
#include <linux/kprobes.h>
#include "kprobes.h"
#ifndef find_str_pc_offset
/*
* For STR and STM instructions, an ARM core may choose to use either
* a +8 or a +12 displacement from the current instruction's address.
* Whichever value is chosen for a given core, it must be the same for
* both instructions and may not change. This function measures it.
*/
int str_pc_offset;
void __init find_str_pc_offset(void)
{
int addr, scratch, ret;
__asm__ (
"sub %[ret], pc, #4 \n\t"
"str pc, %[addr] \n\t"
"ldr %[scr], %[addr] \n\t"
"sub %[ret], %[scr], %[ret] \n\t"
: [ret] "=r" (ret), [scr] "=r" (scratch), [addr] "+m" (addr));
str_pc_offset = ret;
}
#endif /* !find_str_pc_offset */
#ifndef test_load_write_pc_interworking
bool load_write_pc_interworks;
void __init test_load_write_pc_interworking(void)
{
int arch = cpu_architecture();
BUG_ON(arch == CPU_ARCH_UNKNOWN);
load_write_pc_interworks = arch >= CPU_ARCH_ARMv5T;
}
#endif /* !test_load_write_pc_interworking */
#ifndef test_alu_write_pc_interworking
bool alu_write_pc_interworks;
void __init test_alu_write_pc_interworking(void)
{
int arch = cpu_architecture();
BUG_ON(arch == CPU_ARCH_UNKNOWN);
alu_write_pc_interworks = arch >= CPU_ARCH_ARMv7;
}
#endif /* !test_alu_write_pc_interworking */
void __init arm_kprobe_decode_init(void)
{
find_str_pc_offset();
test_load_write_pc_interworking();
test_alu_write_pc_interworking();
}
static unsigned long __kprobes __check_eq(unsigned long cpsr)
{
return cpsr & PSR_Z_BIT;
}
static unsigned long __kprobes __check_ne(unsigned long cpsr)
{
return (~cpsr) & PSR_Z_BIT;
}
static unsigned long __kprobes __check_cs(unsigned long cpsr)
{
return cpsr & PSR_C_BIT;
}
static unsigned long __kprobes __check_cc(unsigned long cpsr)
{
return (~cpsr) & PSR_C_BIT;
}
static unsigned long __kprobes __check_mi(unsigned long cpsr)
{
return cpsr & PSR_N_BIT;
}
static unsigned long __kprobes __check_pl(unsigned long cpsr)
{
return (~cpsr) & PSR_N_BIT;
}
static unsigned long __kprobes __check_vs(unsigned long cpsr)
{
return cpsr & PSR_V_BIT;
}
static unsigned long __kprobes __check_vc(unsigned long cpsr)
{
return (~cpsr) & PSR_V_BIT;
}
static unsigned long __kprobes __check_hi(unsigned long cpsr)
{
cpsr &= ~(cpsr >> 1); /* PSR_C_BIT &= ~PSR_Z_BIT */
return cpsr & PSR_C_BIT;
}
static unsigned long __kprobes __check_ls(unsigned long cpsr)
{
cpsr &= ~(cpsr >> 1); /* PSR_C_BIT &= ~PSR_Z_BIT */
return (~cpsr) & PSR_C_BIT;
}
static unsigned long __kprobes __check_ge(unsigned long cpsr)
{
cpsr ^= (cpsr << 3); /* PSR_N_BIT ^= PSR_V_BIT */
return (~cpsr) & PSR_N_BIT;
}
static unsigned long __kprobes __check_lt(unsigned long cpsr)
{
cpsr ^= (cpsr << 3); /* PSR_N_BIT ^= PSR_V_BIT */
return cpsr & PSR_N_BIT;
}
static unsigned long __kprobes __check_gt(unsigned long cpsr)
{
unsigned long temp = cpsr ^ (cpsr << 3); /* PSR_N_BIT ^= PSR_V_BIT */
temp |= (cpsr << 1); /* PSR_N_BIT |= PSR_Z_BIT */
return (~temp) & PSR_N_BIT;
}
static unsigned long __kprobes __check_le(unsigned long cpsr)
{
unsigned long temp = cpsr ^ (cpsr << 3); /* PSR_N_BIT ^= PSR_V_BIT */
temp |= (cpsr << 1); /* PSR_N_BIT |= PSR_Z_BIT */
return temp & PSR_N_BIT;
}
static unsigned long __kprobes __check_al(unsigned long cpsr)
{
return true;
}
kprobe_check_cc * const kprobe_condition_checks[16] = {
&__check_eq, &__check_ne, &__check_cs, &__check_cc,
&__check_mi, &__check_pl, &__check_vs, &__check_vc,
&__check_hi, &__check_ls, &__check_ge, &__check_lt,
&__check_gt, &__check_le, &__check_al, &__check_al
};
void __kprobes kprobe_simulate_nop(struct kprobe *p, struct pt_regs *regs)
{
}
void __kprobes kprobe_emulate_none(struct kprobe *p, struct pt_regs *regs)
{
p->ainsn.insn_fn();
}
static void __kprobes simulate_ldm1stm1(struct kprobe *p, struct pt_regs *regs)
{
kprobe_opcode_t insn = p->opcode;
int rn = (insn >> 16) & 0xf;
int lbit = insn & (1 << 20);
int wbit = insn & (1 << 21);
int ubit = insn & (1 << 23);
int pbit = insn & (1 << 24);
long *addr = (long *)regs->uregs[rn];
int reg_bit_vector;
int reg_count;
reg_count = 0;
reg_bit_vector = insn & 0xffff;
while (reg_bit_vector) {
reg_bit_vector &= (reg_bit_vector - 1);
++reg_count;
}
if (!ubit)
addr -= reg_count;
addr += (!pbit == !ubit);
reg_bit_vector = insn & 0xffff;
while (reg_bit_vector) {
int reg = __ffs(reg_bit_vector);
reg_bit_vector &= (reg_bit_vector - 1);
if (lbit)
regs->uregs[reg] = *addr++;
else
*addr++ = regs->uregs[reg];
}
if (wbit) {
if (!ubit)
addr -= reg_count;
addr -= (!pbit == !ubit);
regs->uregs[rn] = (long)addr;
}
}
static void __kprobes simulate_stm1_pc(struct kprobe *p, struct pt_regs *regs)
{
regs->ARM_pc = (long)p->addr + str_pc_offset;
simulate_ldm1stm1(p, regs);
regs->ARM_pc = (long)p->addr + 4;
}
static void __kprobes simulate_ldm1_pc(struct kprobe *p, struct pt_regs *regs)
{
simulate_ldm1stm1(p, regs);
load_write_pc(regs->ARM_pc, regs);
}
static void __kprobes
emulate_generic_r0_12_noflags(struct kprobe *p, struct pt_regs *regs)
{
register void *rregs asm("r1") = regs;
register void *rfn asm("lr") = p->ainsn.insn_fn;
__asm__ __volatile__ (
"stmdb sp!, {%[regs], r11} \n\t"
"ldmia %[regs], {r0-r12} \n\t"
#if __LINUX_ARM_ARCH__ >= 6
"blx %[fn] \n\t"
#else
"str %[fn], [sp, #-4]! \n\t"
"adr lr, 1f \n\t"
"ldr pc, [sp], #4 \n\t"
"1: \n\t"
#endif
"ldr lr, [sp], #4 \n\t" /* lr = regs */
"stmia lr, {r0-r12} \n\t"
"ldr r11, [sp], #4 \n\t"
: [regs] "=r" (rregs), [fn] "=r" (rfn)
: "0" (rregs), "1" (rfn)
: "r0", "r2", "r3", "r4", "r5", "r6", "r7",
"r8", "r9", "r10", "r12", "memory", "cc"
);
}
static void __kprobes
emulate_generic_r2_14_noflags(struct kprobe *p, struct pt_regs *regs)
{
emulate_generic_r0_12_noflags(p, (struct pt_regs *)(regs->uregs+2));
}
static void __kprobes
emulate_ldm_r3_15(struct kprobe *p, struct pt_regs *regs)
{
emulate_generic_r0_12_noflags(p, (struct pt_regs *)(regs->uregs+3));
load_write_pc(regs->ARM_pc, regs);
}
enum kprobe_insn __kprobes
kprobe_decode_ldmstm(kprobe_opcode_t insn, struct arch_specific_insn *asi)
{
kprobe_insn_handler_t *handler = 0;
unsigned reglist = insn & 0xffff;
int is_ldm = insn & 0x100000;
int rn = (insn >> 16) & 0xf;
if (rn <= 12 && (reglist & 0xe000) == 0) {
/* Instruction only uses registers in the range R0..R12 */
handler = emulate_generic_r0_12_noflags;
} else if (rn >= 2 && (reglist & 0x8003) == 0) {
/* Instruction only uses registers in the range R2..R14 */
rn -= 2;
reglist >>= 2;
handler = emulate_generic_r2_14_noflags;
} else if (rn >= 3 && (reglist & 0x0007) == 0) {
/* Instruction only uses registers in the range R3..R15 */
if (is_ldm && (reglist & 0x8000)) {
rn -= 3;
reglist >>= 3;
handler = emulate_ldm_r3_15;
}
}
if (handler) {
/* We can emulate the instruction in (possibly) modified form */
asi->insn[0] = (insn & 0xfff00000) | (rn << 16) | reglist;
asi->insn_handler = handler;
return INSN_GOOD;
}
/* Fallback to slower simulation... */
if (reglist & 0x8000)
handler = is_ldm ? simulate_ldm1_pc : simulate_stm1_pc;
else
handler = simulate_ldm1stm1;
asi->insn_handler = handler;
return INSN_GOOD_NO_SLOT;
}
/*
* 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;
}
}
}
