Commit b735bd3e authored by Josh Poimboeuf's avatar Josh Poimboeuf
Browse files

objtool: Combine UNWIND_HINT_RET_OFFSET and UNWIND_HINT_FUNC 



The ORC metadata generated for UNWIND_HINT_FUNC isn't actually very
func-like.  With certain usages it can cause stack state mismatches
because it doesn't set the return address (CFI_RA).

Also, users of UNWIND_HINT_RET_OFFSET no longer need to set a custom
return stack offset.  Instead they just need to specify a func-like
situation, so the current ret_offset code is hacky for no good reason.

Solve both problems by simplifying the RET_OFFSET handling and
converting it into a more useful UNWIND_HINT_FUNC.

If we end up needing the old 'ret_offset' functionality again in the
future, we should be able to support it pretty easily with the addition
of a custom 'sp_offset' in UNWIND_HINT_FUNC.

Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/db9d1f5d79dddfbb3725ef6d8ec3477ad199948d.1611263462.git.jpoimboe@redhat.com
parent 081df943

arch/x86/include/asm/unwind_hints.h

+2 −11
Original line number Diff line number Diff line
@@ -48,17 +48,8 @@ 
	UNWIND_HINT_REGS base=\base offset=\offset partial=1

.endm



.macro UNWIND_HINT_FUNC sp_offset=8

	UNWIND_HINT sp_reg=ORC_REG_SP sp_offset=\sp_offset type=UNWIND_HINT_TYPE_CALL

.endm



/*

 * RET_OFFSET: Used on instructions that terminate a function; mostly RETURN

 * and sibling calls. On these, sp_offset denotes the expected offset from

 * initial_func_cfi.

 */

.macro UNWIND_HINT_RET_OFFSET sp_offset=8

	UNWIND_HINT sp_reg=ORC_REG_SP type=UNWIND_HINT_TYPE_RET_OFFSET sp_offset=\sp_offset

.macro UNWIND_HINT_FUNC

	UNWIND_HINT sp_reg=ORC_REG_SP sp_offset=8 type=UNWIND_HINT_TYPE_FUNC

.endm



#endif /* __ASSEMBLY__ */

arch/x86/kernel/ftrace_64.S

+1 −1
Original line number Diff line number Diff line
@@ -277,7 +277,7 @@ SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL) 
	restore_mcount_regs 8

	/* Restore flags */

	popfq

	UNWIND_HINT_RET_OFFSET

	UNWIND_HINT_FUNC

	jmp	ftrace_epilogue



SYM_FUNC_END(ftrace_regs_caller)

arch/x86/lib/retpoline.S

+1 −1
Original line number Diff line number Diff line
@@ -28,7 +28,7 @@ SYM_FUNC_START_NOALIGN(__x86_retpoline_\reg) 
	jmp	.Lspec_trap_\@

.Ldo_rop_\@:

	mov	%\reg, (%_ASM_SP)

	UNWIND_HINT_RET_OFFSET

	UNWIND_HINT_FUNC

	ret

SYM_FUNC_END(__x86_retpoline_\reg)

include/linux/objtool.h

+4 −1
Original line number Diff line number Diff line
@@ -29,11 +29,14 @@ struct unwind_hint { 
 *

 * UNWIND_HINT_TYPE_REGS_PARTIAL: Used in entry code to indicate that

 * sp_reg+sp_offset points to the iret return frame.

 *

 * UNWIND_HINT_FUNC: Generate the unwind metadata of a callable function.

 * Useful for code which doesn't have an ELF function annotation.

 */

#define UNWIND_HINT_TYPE_CALL		0

#define UNWIND_HINT_TYPE_REGS		1

#define UNWIND_HINT_TYPE_REGS_PARTIAL	2

#define UNWIND_HINT_TYPE_RET_OFFSET	3

#define UNWIND_HINT_TYPE_FUNC		3



#ifdef CONFIG_STACK_VALIDATION

tools/include/linux/objtool.h

+4 −1
Original line number Diff line number Diff line
@@ -29,11 +29,14 @@ struct unwind_hint { 
 *

 * UNWIND_HINT_TYPE_REGS_PARTIAL: Used in entry code to indicate that

 * sp_reg+sp_offset points to the iret return frame.

 *

 * UNWIND_HINT_FUNC: Generate the unwind metadata of a callable function.

 * Useful for code which doesn't have an ELF function annotation.

 */

#define UNWIND_HINT_TYPE_CALL		0

#define UNWIND_HINT_TYPE_REGS		1

#define UNWIND_HINT_TYPE_REGS_PARTIAL	2

#define UNWIND_HINT_TYPE_RET_OFFSET	3

#define UNWIND_HINT_TYPE_FUNC		3



#ifdef CONFIG_STACK_VALIDATION