Commit 1cc1e4c8 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Borislav Petkov
Browse files

objtool: Add straight-line-speculation validation 



Teach objtool to validate the straight-line-speculation constraints:

 - speculation trap after indirect calls
 - speculation trap after RET

Notable: when an instruction is annotated RETPOLINE_SAFE, indicating
  speculation isn't a problem, also don't care about sls for that
  instruction.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20211204134908.023037659@infradead.org
parent b17c2baa

tools/objtool/arch/x86/decode.c

+9 −4
Original line number Diff line number Diff line
@@ -531,6 +531,11 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec 
		}

		break;



	case 0xcc:

		/* int3 */

		*type = INSN_TRAP;

		break;



	case 0xe3:

		/* jecxz/jrcxz */

		*type = INSN_JUMP_CONDITIONAL;
@@ -697,10 +702,10 @@ const char *arch_ret_insn(int len) 
{

	static const char ret[5][5] = {

		{ BYTE_RET },

		{ BYTE_RET, BYTES_NOP1 },

		{ BYTE_RET, BYTES_NOP2 },

		{ BYTE_RET, BYTES_NOP3 },

		{ BYTE_RET, BYTES_NOP4 },

		{ BYTE_RET, 0xcc },

		{ BYTE_RET, 0xcc, BYTES_NOP1 },

		{ BYTE_RET, 0xcc, BYTES_NOP2 },

		{ BYTE_RET, 0xcc, BYTES_NOP3 },

	};



	if (len < 1 || len > 5) {

tools/objtool/builtin-check.c

+2 −1
Original line number Diff line number Diff line
@@ -20,7 +20,7 @@ 
#include <objtool/objtool.h>



bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,

     validate_dup, vmlinux, mcount, noinstr, backup;

     validate_dup, vmlinux, mcount, noinstr, backup, sls;



static const char * const check_usage[] = {

	"objtool check [<options>] file.o",
@@ -45,6 +45,7 @@ const struct option check_options[] = { 
	OPT_BOOLEAN('l', "vmlinux", &vmlinux, "vmlinux.o validation"),

	OPT_BOOLEAN('M', "mcount", &mcount, "generate __mcount_loc"),

	OPT_BOOLEAN('B', "backup", &backup, "create .orig files before modification"),

	OPT_BOOLEAN('S', "sls", &sls, "validate straight-line-speculation"),

	OPT_END(),

};

tools/objtool/check.c

+14 −0
Original line number Diff line number Diff line
@@ -3084,6 +3084,12 @@ static int validate_branch(struct objtool_file *file, struct symbol *func, 
		switch (insn->type) {



		case INSN_RETURN:

			if (next_insn && next_insn->type == INSN_TRAP) {

				next_insn->ignore = true;

			} else if (sls && !insn->retpoline_safe) {

				WARN_FUNC("missing int3 after ret",

					  insn->sec, insn->offset);

			}

			return validate_return(func, insn, &state);



		case INSN_CALL:
@@ -3127,6 +3133,14 @@ static int validate_branch(struct objtool_file *file, struct symbol *func, 
			break;



		case INSN_JUMP_DYNAMIC:

			if (next_insn && next_insn->type == INSN_TRAP) {

				next_insn->ignore = true;

			} else if (sls && !insn->retpoline_safe) {

				WARN_FUNC("missing int3 after indirect jump",

					  insn->sec, insn->offset);

			}



			/* fallthrough */

		case INSN_JUMP_DYNAMIC_CONDITIONAL:

			if (is_sibling_call(insn)) {

				ret = validate_sibling_call(file, insn, &state);

tools/objtool/include/objtool/arch.h

+1 −0
Original line number Diff line number Diff line
@@ -26,6 +26,7 @@ enum insn_type { 
	INSN_CLAC,

	INSN_STD,

	INSN_CLD,

	INSN_TRAP,

	INSN_OTHER,

};

tools/objtool/include/objtool/builtin.h

+1 −1
Original line number Diff line number Diff line
@@ -9,7 +9,7 @@ 


extern const struct option check_options[];

extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,

            validate_dup, vmlinux, mcount, noinstr, backup;

            validate_dup, vmlinux, mcount, noinstr, backup, sls;



extern int cmd_parse_options(int argc, const char **argv, const char * const usage[]);