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#include <sys/mman.h>
#include <sys/resource.h>
#include "instrument.h"
#include "util.h"
#if defined(__x86_64__)
#define INVALID 1
#define DEFAULT_CACHE_SIZE (256ULL << 20)
gboolean instrument_cache_enabled = TRUE;
gsize instrument_cache_size = DEFAULT_CACHE_SIZE;
static gpointer *map_base = MAP_FAILED;
void instrument_cache_config(void) {
instrument_cache_enabled = (getenv("AFL_FRIDA_INST_NO_CACHE") == NULL);
if (getenv("AFL_FRIDA_INST_CACHE_SIZE") != NULL) {
if (!instrument_cache_enabled) {
FFATAL(
"AFL_FRIDA_INST_CACHE_SIZE incomatible with "
"AFL_FRIDA_INST_NO_CACHE");
}
instrument_cache_size =
util_read_address("AFL_FRIDA_INST_CACHE_SIZE", DEFAULT_CACHE_SIZE);
util_log2(instrument_cache_size);
}
}
void instrument_cache_init(void) {
FOKF(cBLU "Instrumentation" cRST " - " cGRN "cache:" cYEL " [%c]",
instrument_cache_enabled ? 'X' : ' ');
if (!instrument_cache_enabled) { return; }
FOKF(cBLU "Instrumentation" cRST " - " cGRN "cache size:" cYEL " [0x%016lX]",
instrument_cache_size);
const struct rlimit data_limit = {.rlim_cur = RLIM_INFINITY,
.rlim_max = RLIM_INFINITY};
if (setrlimit(RLIMIT_AS, &data_limit) != 0) {
FFATAL("Failed to setrlimit: %d", errno);
}
map_base =
gum_memory_allocate(NULL, instrument_cache_size, instrument_cache_size,
GUM_PAGE_READ | GUM_PAGE_WRITE);
if (map_base == MAP_FAILED) { FFATAL("Failed to map segment: %d", errno); }
FOKF(cBLU "Instrumentation" cRST " - " cGRN "cache addr:" cYEL " [0x%016lX]",
GUM_ADDRESS(map_base));
}
static gpointer *instrument_cache_get_addr(gpointer addr) {
gsize mask = (instrument_cache_size / sizeof(gpointer)) - 1;
return &map_base[GPOINTER_TO_SIZE(addr) & mask];
}
void instrument_cache_insert(gpointer real_address, gpointer code_address) {
if (!instrument_cache_enabled) { return; }
gpointer *target = instrument_cache_get_addr(real_address);
if (*target == code_address) {
return;
} else if (*target == NULL) {
*target = code_address;
} else {
*target = GSIZE_TO_POINTER(INVALID);
}
}
static gboolean instrument_cache_relocate(GumAddress old_pc, GumAddress new_pc,
gint32 old_offset,
gint32 *new_offset) {
guint64 old_target = old_pc + old_offset;
gint64 relocated = old_target - new_pc;
if (relocated > G_MAXINT32 || relocated < G_MININT32) { return FALSE; }
*new_offset = relocated;
return TRUE;
}
static void instrument_cache_rewrite_branch_insn(const cs_insn *instr,
GumStalkerOutput *output) {
GumX86Writer *cw = output->writer.x86;
cs_x86 *x86 = &instr->detail->x86;
guint8 modified[sizeof(instr->bytes)] = {0};
guint8 offset = 0;
guint8 skip = 0;
g_assert(sizeof(x86->prefix) == 4);
g_assert(sizeof(x86->opcode) == 4);
/*
* If the target is simply RAX, we can skip writing the code to load the
* RIP
*/
if (x86->operands[0].type == X86_OP_REG ||
x86->operands[0].reg == X86_REG_RAX) {
return;
}
/* Write the prefix */
for (gsize i = 0; i < sizeof(x86->prefix); i++) {
if (x86->prefix[i] != 0) {
if (x86->prefix[i] == 0xf2) {
skip++;
} else {
modified[offset++] = x86->prefix[i];
skip++;
}
}
}
/* Write the REX */
if (x86->rex == 0) {
/*
* CALL (near) and JMP (near) default to 64-bit operands, MOV does not,
* write REX.W
*/
modified[offset++] = 0x48;
} else {
if ((x86->rex & 0xF8) != 0x40) {
FATAL("Unexpected REX byte: 0x%02x", x86->rex);
}
modified[offset++] = x86->rex | 0x08;
skip++;
}
/*
* CALL is FF /2, JMP is FF /4. The remaining op-code fields should thus be
* unused
*/
if (x86->opcode[0] != 0xFF || x86->opcode[1] != 0x00 ||
x86->opcode[2] != 0x00 || x86->opcode[3] != 0x00) {
FFATAL("Unexpected Op-code: 0x%02x 0x%02x 0x%02x 0x%02x", x86->opcode[0],
x86->opcode[1], x86->opcode[2], x86->opcode[3]);
}
/* The reg field of the ModRM should be set to 2 for CALL and 4 for JMP */
guint8 reg = (x86->modrm >> 3) & 7;
if (reg != 0x4 && reg != 0x2) {
FFATAL("Unexpected Reg: 0x%02x, ModRM: 0x%02x", reg, x86->modrm);
}
/* MOV */
modified[offset++] = 0x8b;
skip++;
/* Clear the reg field (RAX) */
modified[offset++] = x86->modrm & 0xc7;
skip++;
/* Operands */
guint8 op_len = instr->size - skip;
/* If our branch was RIP relative, we'll need to fix-up the offset */
if (x86->operands[0].type == X86_OP_MEM &&
x86->operands[0].mem.base == X86_REG_RIP) {
/* RIP relative offsets should be 32-bits */
if (op_len != sizeof(gint32)) {
FFATAL("Unexpected operand length: %d\n", op_len);
}
gint32 old_offset = *(gint32 *)&instr->bytes[skip];
gint32 new_offset = 0;
if (instrument_cache_relocate(instr->address, cw->pc, old_offset,
&new_offset)) {
gint32 *output = (gint32 *)&modified[offset];
*output = new_offset;
offset += sizeof(gint32);
} else {
GumAddress target = instr->address + old_offset;
gum_x86_writer_put_mov_reg_address(cw, GUM_X86_RAX, target);
gum_x86_writer_put_mov_reg_reg_ptr(cw, GUM_X86_RAX, GUM_X86_RAX);
return;
}
} else {
for (int i = 0; i < op_len; i++) {
guint8 val = instr->bytes[i + skip];
modified[offset++] = val;
}
}
gum_x86_writer_put_bytes(cw, modified, offset);
}
static void instrument_cache_write_push_frame(GumX86Writer *cw) {
gum_x86_writer_put_mov_reg_offset_ptr_reg(
cw, GUM_X86_XSP, -(GUM_RED_ZONE_SIZE + (1 * sizeof(gpointer))),
GUM_X86_XAX);
gum_x86_writer_put_lahf(cw);
gum_x86_writer_put_mov_reg_offset_ptr_reg(
cw, GUM_X86_XSP, -(GUM_RED_ZONE_SIZE + (2 * sizeof(gpointer))),
GUM_X86_XAX);
gum_x86_writer_put_mov_reg_offset_ptr_reg(
cw, GUM_X86_XSP, -(GUM_RED_ZONE_SIZE + (3 * sizeof(gpointer))),
GUM_X86_XBX);
}
static void instrument_cache_write_pop_frame(GumX86Writer *cw) {
gum_x86_writer_put_mov_reg_reg_offset_ptr(
cw, GUM_X86_XBX, GUM_X86_XSP,
-(GUM_RED_ZONE_SIZE + (3 * sizeof(gpointer))));
gum_x86_writer_put_mov_reg_reg_offset_ptr(
cw, GUM_X86_XAX, GUM_X86_XSP,
-(GUM_RED_ZONE_SIZE + (2 * sizeof(gpointer))));
gum_x86_writer_put_sahf(cw);
gum_x86_writer_put_mov_reg_reg_offset_ptr(
cw, GUM_X86_XAX, GUM_X86_XSP,
-(GUM_RED_ZONE_SIZE + (1 * sizeof(gpointer))));
}
static void instrument_cache_write_lookup(GumX86Writer *cw) {
/* &map_base[GPOINTER_TO_SIZE(addr) & MAP_MASK]; */
gsize mask = (instrument_cache_size / sizeof(gpointer)) - 1;
gum_x86_writer_put_mov_reg_u64(cw, GUM_X86_XBX, mask);
gum_x86_writer_put_and_reg_reg(cw, GUM_X86_XAX, GUM_X86_XBX);
gum_x86_writer_put_shl_reg_u8(cw, GUM_X86_XAX, util_log2(sizeof(gpointer)));
gum_x86_writer_put_mov_reg_u64(cw, GUM_X86_XBX, GPOINTER_TO_SIZE(map_base));
gum_x86_writer_put_add_reg_reg(cw, GUM_X86_XAX, GUM_X86_XBX);
/* Read the return address lookup */
gum_x86_writer_put_mov_reg_reg_ptr(cw, GUM_X86_XAX, GUM_X86_XAX);
}
void instrument_cache_jmp_call(const cs_insn *instr, GumStalkerOutput *output) {
GumX86Writer *cw = output->writer.x86;
cs_x86 *x86 = &instr->detail->x86;
if (x86->op_count != 1) { FFATAL("Unexpected operand count"); }
if (x86->operands[0].type == X86_OP_IMM) { return; }
gconstpointer null = cw->code;
instrument_cache_write_push_frame(cw);
/*
* We are about to re-write the CALL or JMP instruction, but replace the
* op-code with that for a MOV into RAX. Since we are keeping the operand from
* the JMP exactly the same, it is imperative that the target register state
* be exactly the same as how the target left it. Since `LAHF` spoils `RAX` we
* must restore it from the stack. We also must avoid adjusting `RSP`, so we
* use `MOV` instructions to store our context into the stack beyond the
* red-zone.
*/
gum_x86_writer_put_mov_reg_reg_offset_ptr(
cw, GUM_X86_XAX, GUM_X86_XSP,
-(GUM_RED_ZONE_SIZE + (1 * sizeof(gpointer))));
instrument_cache_rewrite_branch_insn(instr, output);
instrument_cache_write_lookup(cw);
/* Test if its set*/
gum_x86_writer_put_cmp_reg_i32(cw, GUM_X86_XAX, INVALID);
gum_x86_writer_put_jcc_short_label(cw, X86_INS_JLE, null, GUM_UNLIKELY);
/* If it's set, then stash the address beyond the red-zone */
gum_x86_writer_put_mov_reg_offset_ptr_reg(
cw, GUM_X86_XSP, -(GUM_RED_ZONE_SIZE + (4 * sizeof(gpointer))),
GUM_X86_XAX);
if (instr->id == X86_INS_JMP) {
instrument_cache_write_pop_frame(cw);
gum_x86_writer_put_jmp_reg_offset_ptr(
cw, GUM_X86_XSP, -(GUM_RED_ZONE_SIZE + (4 * sizeof(gpointer))));
} else {
gum_x86_writer_put_mov_reg_address(
cw, GUM_X86_XAX, GUM_ADDRESS(instr->address + instr->size));
gum_x86_writer_put_mov_reg_offset_ptr_reg(cw, GUM_X86_XSP,
-sizeof(gpointer), GUM_X86_XAX);
instrument_cache_write_pop_frame(cw);
gum_x86_writer_put_lea_reg_reg_offset(cw, GUM_X86_XSP, GUM_X86_XSP,
-sizeof(gpointer));
gum_x86_writer_put_jmp_reg_offset_ptr(
cw, GUM_X86_XSP, -(GUM_RED_ZONE_SIZE + ((4 - 1) * sizeof(gpointer))));
}
/* Tidy up our mess and let FRIDA handle it */
gum_x86_writer_put_label(cw, null);
instrument_cache_write_pop_frame(cw);
}
void instrument_cache_ret(const cs_insn *instr, GumStalkerOutput *output) {
GumX86Writer *cw = output->writer.x86;
cs_x86 *x86 = &instr->detail->x86;
guint16 n = 0;
if (x86->op_count != 0) {
if (x86->operands[0].type != X86_OP_IMM) {
FFATAL("Unexpected operand type");
}
n = x86->operands[0].imm;
}
gconstpointer null = cw->code;
instrument_cache_write_push_frame(cw);
gum_x86_writer_put_mov_reg_reg_ptr(cw, GUM_X86_XAX, GUM_X86_XSP);
instrument_cache_write_lookup(cw);
/* Test if its set*/
gum_x86_writer_put_cmp_reg_i32(cw, GUM_X86_XAX, INVALID);
gum_x86_writer_put_jcc_short_label(cw, X86_INS_JLE, null, GUM_UNLIKELY);
/* If it's set, then overwrite our return address and return */
gum_x86_writer_put_mov_reg_ptr_reg(cw, GUM_X86_XSP, GUM_X86_XAX);
instrument_cache_write_pop_frame(cw);
if (n == 0) {
gum_x86_writer_put_ret(cw);
} else {
gum_x86_writer_put_ret_imm(cw, n);
}
/* Tidy up our mess and let FRIDA handle it */
gum_x86_writer_put_label(cw, null);
instrument_cache_write_pop_frame(cw);
}
void instrument_cache(const cs_insn *instr, GumStalkerOutput *output) {
if (!instrument_cache_enabled) { return; }
switch (instr->id) {
case X86_INS_RET:
instrument_cache_ret(instr, output);
break;
case X86_INS_CALL:
case X86_INS_JMP:
instrument_cache_jmp_call(instr, output);
break;
default:
return;
}
}
#endif
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