// SPDX-License-Identifier: GPL-2.0-only
/*
* arch/arm/probes/decode.c
*
* Copyright (C) 2011 Jon Medhurst <[email protected]>.
*
* Some contents moved here from arch/arm/include/asm/kprobes-arm.c which is
* Copyright (C) 2006, 2007 Motorola Inc.
*/
#include <linux/kernel.h>
#include <linux/types.h>
#include <asm/system_info.h>
#include <asm/ptrace.h>
#include <linux/bug.h>
#include "decode.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_probes_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;
}
probes_check_cc * const probes_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 probes_simulate_nop(probes_opcode_t opcode,
struct arch_probes_insn *asi,
struct pt_regs *regs)
{
}
void __kprobes probes_emulate_none(probes_opcode_t opcode,
struct arch_probes_insn *asi,
struct pt_regs *regs)
{
asi->insn_fn();
}
/*
* 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 probes_opcode_t __kprobes
prepare_emulated_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
bool thumb)
{
#ifdef CONFIG_THUMB2_KERNEL
if (thumb) {
u16 *thumb_insn = (u16 *)asi->insn;
/* Thumb bx lr */
thumb_insn[1] = __opcode_to_mem_thumb16(0x4770);
thumb_insn[2] = __opcode_to_mem_thumb16(0x4770);
return insn;
}
asi->insn[1] = __opcode_to_mem_arm(0xe12fff1e); /* ARM bx lr */
#else
asi->insn[1] = __opcode_to_mem_arm(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(probes_opcode_t insn, struct arch_probes_insn *asi,
bool thumb)
{
#ifdef CONFIG_THUMB2_KERNEL
if (thumb) {
u16 *ip = (u16 *)asi->insn;
if (is_wide_instruction(insn))
*ip++ = __opcode_to_mem_thumb16(insn >> 16);
*ip++ = __opcode_to_mem_thumb16(insn);
return;
}
#endif
asi->insn[0] = __opcode_to_mem_arm(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(probes_opcode_t *pinsn, u32 regs, bool modify)
{
probes_opcode_t insn = *pinsn;
probes_opcode_t mask = 0xf; /* Start at least significant nibble */
for (; regs != 0; regs >>= 4, mask <<= 4) {
probes_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 */
fallthrough;
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;
}
if (modify)
*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)
};
static int run_checkers(const struct decode_checker *checkers[],
int action, probes_opcode_t insn,
struct arch_probes_insn *asi,
const struct decode_header *h)
{
const struct decode_checker **p;
if (!checkers)
return INSN_GOOD;
p = checkers;
while (*p != NULL) {
int retval;
probes_check_t *checker_func = (*p)[action].checker;
retval = INSN_GOOD;
if (checker_func)
retval = checker_func(insn, asi, h);
if (retval == INSN_REJECTED)
return retval;
p++;
}
return INSN_GOOD;
}
/*
* probes_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
probes_decode_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
const union decode_item *table, bool thumb,
bool emulate, const union decode_action *actions,
const struct decode_checker *checkers[])
{
const struct decode_header *h = (struct decode_header *)table;
const struct decode_header *next;
bool matched = false;
/*
* @insn can be modified by decode_regs. Save its original
* value for checkers.
*/
probes_opcode_t origin_insn = insn;
/*
* stack_space is initialized to 0 here. Checker functions
* should update is value if they find this is a stack store
* instruction: positive value means bytes of stack usage,
* negitive value means unable to determine stack usage
* statically. For instruction doesn't store to stack, checker
* do nothing with it.
*/
asi->stack_space = 0;
/*
* Similarly to stack_space, register_usage_flags is filled by
* checkers. Its default value is set to ~0, which is 'all
* registers are used', to prevent any potential optimization.
*/
asi->register_usage_flags = ~0UL;
if (emulate)
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, emulate))
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: {
int err;
struct decode_custom *d = (struct decode_custom *)h;
int action = d->decoder.action;
err = run_checkers(checkers, action, origin_insn, asi, h);
if (err == INSN_REJECTED)
return INSN_REJECTED;
return actions[action].decoder(insn, asi, h);
}
case DECODE_TYPE_SIMULATE: {
int err;
struct decode_simulate *d = (struct decode_simulate *)h;
int action = d->handler.action;
err = run_checkers(checkers, action, origin_insn, asi, h);
if (err == INSN_REJECTED)
return INSN_REJECTED;
asi->insn_handler = actions[action].handler;
return INSN_GOOD_NO_SLOT;
}
case DECODE_TYPE_EMULATE: {
int err;
struct decode_emulate *d = (struct decode_emulate *)h;
int action = d->handler.action;
err = run_checkers(checkers, action, origin_insn, asi, h);
if (err == INSN_REJECTED)
return INSN_REJECTED;
if (!emulate)
return actions[action].decoder(insn, asi, h);
asi->insn_handler = actions[action].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;
}
}
}
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