[PATCH v3 35/39] objtool: Add IBT/ENDBR decoding

Peter Zijlstra
2022-03-03T11:33:16Z

Decode ENDBR instructions and WARN about NOTRACK prefixes.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
tools/objtool/arch/x86/decode.c | 34 +++++++++++++++++++++++++++++-----
tools/objtool/include/objtool/arch.h | 1 +
2 files changed, 30 insertions(+), 5 deletions(-)

--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -103,6 +103,18 @@ unsigned long arch_jump_destination(stru
#define rm_is_mem(reg) (mod_is_mem() && !is_RIP() && rm_is(reg))
#define rm_is_reg(reg) (mod_is_reg() && modrm_rm == (reg))

+static bool has_notrack_prefix(struct insn *insn)
+{
+ int i;
+
+ for (i = 0; i < insn->prefixes.nbytes; i++) {
+ if (insn->prefixes.bytes[i] == 0x3e)
+ return true;
+ }
+
+ return false;
+}
+
int arch_decode_instruction(struct objtool_file *file, const struct section *sec,
unsigned long offset, unsigned int maxlen,
unsigned int *len, enum insn_type *type,
@@ -112,7 +124,7 @@ int arch_decode_instruction(struct objto
const struct elf *elf = file->elf;
struct insn insn;
int x86_64, ret;
- unsigned char op1, op2, op3,
+ unsigned char op1, op2, op3, prefix,
rex = 0, rex_b = 0, rex_r = 0, rex_w = 0, rex_x = 0,
modrm = 0, modrm_mod = 0, modrm_rm = 0, modrm_reg = 0,
sib = 0, /* sib_scale = 0, */ sib_index = 0, sib_base = 0;
@@ -137,6 +149,8 @@ int arch_decode_instruction(struct objto
if (insn.vex_prefix.nbytes)
return 0;

+ prefix = insn.prefixes.bytes[0];
+
op1 = insn.opcode.bytes[0];
op2 = insn.opcode.bytes[1];
op3 = insn.opcode.bytes[2];
@@ -492,6 +506,12 @@ int arch_decode_instruction(struct objto
/* nopl/nopw */
*type = INSN_NOP;

+ } else if (op2 == 0x1e) {
+
+ if (prefix == 0xf3 && (modrm == 0xfa || modrm == 0xfb))
+ *type = INSN_ENDBR;
+
+
} else if (op2 == 0x38 && op3 == 0xf8) {
if (insn.prefixes.nbytes == 1 &&
insn.prefixes.bytes[0] == 0xf2) {
@@ -636,20 +656,24 @@ int arch_decode_instruction(struct objto
break;

case 0xff:
- if (modrm_reg == 2 || modrm_reg == 3)
+ if (modrm_reg == 2 || modrm_reg == 3) {

*type = INSN_CALL_DYNAMIC;
+ if (has_notrack_prefix(&insn))
+ WARN("notrack prefix found at %s:0x%lx", sec->name, offset);

- else if (modrm_reg == 4)
+ } else if (modrm_reg == 4) {

*type = INSN_JUMP_DYNAMIC;
+ if (has_notrack_prefix(&insn))
+ WARN("notrack prefix found at %s:0x%lx", sec->name, offset);

- else if (modrm_reg == 5)
+ } else if (modrm_reg == 5) {

/* jmpf */
*type = INSN_CONTEXT_SWITCH;

- else if (modrm_reg == 6) {
+ } else if (modrm_reg == 6) {

/* push from mem */
ADD_OP(op) {
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -27,6 +27,7 @@ enum insn_type {
INSN_STD,
INSN_CLD,
INSN_TRAP,
+ INSN_ENDBR,
INSN_OTHER,
};