diff options
Diffstat (limited to 'arch/x86/lib/insn-eval.c')
| -rw-r--r-- | arch/x86/lib/insn-eval.c | 151 |
1 files changed, 147 insertions, 4 deletions
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 4e385cbfd444..e03eeec55cfe 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -63,11 +63,10 @@ static bool is_string_insn(struct insn *insn) bool insn_has_rep_prefix(struct insn *insn) { insn_byte_t p; - int i; insn_get_prefixes(insn); - for_each_insn_prefix(insn, i, p) { + for_each_insn_prefix(insn, p) { if (p == 0xf2 || p == 0xf3) return true; } @@ -92,13 +91,13 @@ bool insn_has_rep_prefix(struct insn *insn) static int get_seg_reg_override_idx(struct insn *insn) { int idx = INAT_SEG_REG_DEFAULT; - int num_overrides = 0, i; + int num_overrides = 0; insn_byte_t p; insn_get_prefixes(insn); /* Look for any segment override prefixes. */ - for_each_insn_prefix(insn, i, p) { + for_each_insn_prefix(insn, p) { insn_attr_t attr; attr = inat_get_opcode_attribute(p); @@ -1676,3 +1675,147 @@ enum insn_mmio_type insn_decode_mmio(struct insn *insn, int *bytes) return type; } + +/* + * Recognise typical NOP patterns for both 32bit and 64bit. + * + * Notably: + * - NOP, but not: REP NOP aka PAUSE + * - NOPL + * - MOV %reg, %reg + * - LEA 0(%reg),%reg + * - JMP +0 + * + * Must not have false-positives; instructions identified as a NOP might be + * emulated as a NOP (uprobe) or Run Length Encoded in a larger NOP + * (alternatives). + * + * False-negatives are fine; need not be exhaustive. + */ +bool insn_is_nop(struct insn *insn) +{ + u8 b3 = 0, x3 = 0, r3 = 0; + u8 b4 = 0, x4 = 0, r4 = 0, m = 0; + u8 modrm, modrm_mod, modrm_reg, modrm_rm; + u8 sib = 0, sib_scale, sib_index, sib_base; + u8 nrex, rex; + u8 p, rep = 0; + + if ((nrex = insn->rex_prefix.nbytes)) { + rex = insn->rex_prefix.bytes[nrex-1]; + + r3 = !!X86_REX_R(rex); + x3 = !!X86_REX_X(rex); + b3 = !!X86_REX_B(rex); + if (nrex > 1) { + r4 = !!X86_REX2_R(rex); + x4 = !!X86_REX2_X(rex); + b4 = !!X86_REX2_B(rex); + m = !!X86_REX2_M(rex); + } + + } else if (insn->vex_prefix.nbytes) { + /* + * Ignore VEX encoded NOPs + */ + return false; + } + + if (insn->modrm.nbytes) { + modrm = insn->modrm.bytes[0]; + modrm_mod = X86_MODRM_MOD(modrm); + modrm_reg = X86_MODRM_REG(modrm) + 8*r3 + 16*r4; + modrm_rm = X86_MODRM_RM(modrm) + 8*b3 + 16*b4; + modrm = 1; + } + + if (insn->sib.nbytes) { + sib = insn->sib.bytes[0]; + sib_scale = X86_SIB_SCALE(sib); + sib_index = X86_SIB_INDEX(sib) + 8*x3 + 16*x4; + sib_base = X86_SIB_BASE(sib) + 8*b3 + 16*b4; + sib = 1; + + modrm_rm = sib_base; + } + + for_each_insn_prefix(insn, p) { + if (p == 0xf3) /* REPE */ + rep = 1; + } + + /* + * Opcode map munging: + * + * REX2: 0 - single byte opcode + * 1 - 0f second byte opcode + */ + switch (m) { + case 0: break; + case 1: insn->opcode.value <<= 8; + insn->opcode.value |= 0x0f; + break; + default: + return false; + } + + switch (insn->opcode.bytes[0]) { + case 0x0f: /* 2nd byte */ + break; + + case 0x89: /* MOV */ + if (modrm_mod != 3) /* register-direct */ + return false; + + /* native size */ + if (insn->opnd_bytes != 4 * (1 + insn->x86_64)) + return false; + + return modrm_reg == modrm_rm; /* MOV %reg, %reg */ + + case 0x8d: /* LEA */ + if (modrm_mod == 0 || modrm_mod == 3) /* register-indirect with disp */ + return false; + + /* native size */ + if (insn->opnd_bytes != 4 * (1 + insn->x86_64)) + return false; + + if (insn->displacement.value != 0) + return false; + + if (sib && (sib_scale != 0 || sib_index != 4)) /* (%reg, %eiz, 1) */ + return false; + + for_each_insn_prefix(insn, p) { + if (p != 0x3e) /* DS */ + return false; + } + + return modrm_reg == modrm_rm; /* LEA 0(%reg), %reg */ + + case 0x90: /* NOP */ + if (b3 || b4) /* XCHG %r{8,16,24},%rax */ + return false; + + if (rep) /* REP NOP := PAUSE */ + return false; + + return true; + + case 0xe9: /* JMP.d32 */ + case 0xeb: /* JMP.d8 */ + return insn->immediate.value == 0; /* JMP +0 */ + + default: + return false; + } + + switch (insn->opcode.bytes[1]) { + case 0x1f: + return modrm_reg == 0; /* 0f 1f /0 -- NOPL */ + + default: + return false; + } +} |