Commit 7d209d13 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

objtool: Add IBT/ENDBR decoding 



Intel IBT requires the target of any indirect CALL or JMP instruction
to be the ENDBR instruction; optionally it allows those two
instructions to have a NOTRACK prefix in order to avoid this
requirement.

The kernel will not enable the use of NOTRACK, as such any occurence
of it in compiler generated code should be flagged.

Teach objtool to Decode ENDBR instructions and WARN about NOTRACK
prefixes.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154319.645963517@infradead.org
parent 96db4a98

tools/objtool/arch/x86/decode.c

+29 −5
Original line number Diff line number Diff line
@@ -103,6 +103,18 @@ unsigned long arch_jump_destination(struct instruction *insn) 
#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 objtool_file *file, const struct section *sec 
	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 objtool_file *file, const struct section *sec 
	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 objtool_file *file, const struct section *sec 
			/* 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 objtool_file *file, const struct section *sec 
		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) {

tools/objtool/include/objtool/arch.h

+1 −0
Original line number Diff line number Diff line
@@ -27,6 +27,7 @@ enum insn_type { 
	INSN_STD,

	INSN_CLD,

	INSN_TRAP,

	INSN_ENDBR,

	INSN_OTHER,

};