Commit 2d12c6fb authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar
Browse files

objtool: Remove ANNOTATE_IGNORE_ALTERNATIVE from CLAC/STAC 



ANNOTATE_IGNORE_ALTERNATIVE adds additional noise to the code generated
by CLAC/STAC alternatives, hurting readability for those whose read
uaccess-related code generation on a regular basis.

Remove the annotation specifically for the "NOP patched with CLAC/STAC"
case in favor of a manual check.

Leave the other uses of that annotation in place as they're less common
and more difficult to detect.

Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/fc972ba4995d826fcfb8d02733a14be8d670900b.1744098446.git.jpoimboe@kernel.org
parent 2dbbca9b

arch/x86/include/asm/smap.h

+6 −6
Original line number Diff line number Diff line
@@ -16,23 +16,23 @@ 
#ifdef __ASSEMBLER__



#define ASM_CLAC \

	ALTERNATIVE __stringify(ANNOTATE_IGNORE_ALTERNATIVE), "clac", X86_FEATURE_SMAP

	ALTERNATIVE "", "clac", X86_FEATURE_SMAP



#define ASM_STAC \

	ALTERNATIVE __stringify(ANNOTATE_IGNORE_ALTERNATIVE), "stac", X86_FEATURE_SMAP

	ALTERNATIVE "", "stac", X86_FEATURE_SMAP



#else /* __ASSEMBLER__ */



static __always_inline void clac(void)

{

	/* Note: a barrier is implicit in alternative() */

	alternative(ANNOTATE_IGNORE_ALTERNATIVE "", "clac", X86_FEATURE_SMAP);

	alternative("", "clac", X86_FEATURE_SMAP);

}



static __always_inline void stac(void)

{

	/* Note: a barrier is implicit in alternative() */

	alternative(ANNOTATE_IGNORE_ALTERNATIVE "", "stac", X86_FEATURE_SMAP);

	alternative("", "stac", X86_FEATURE_SMAP);

}



static __always_inline unsigned long smap_save(void)
@@ -59,9 +59,9 @@ static __always_inline void smap_restore(unsigned long flags) 


/* These macros can be used in asm() statements */

#define ASM_CLAC \

	ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE "", "clac", X86_FEATURE_SMAP)

	ALTERNATIVE("", "clac", X86_FEATURE_SMAP)

#define ASM_STAC \

	ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE "", "stac", X86_FEATURE_SMAP)

	ALTERNATIVE("", "stac", X86_FEATURE_SMAP)



#define ASM_CLAC_UNSAFE \

	ALTERNATIVE("", ANNOTATE_IGNORE_ALTERNATIVE "clac", X86_FEATURE_SMAP)

tools/objtool/check.c

+29 −1
Original line number Diff line number Diff line
@@ -3505,6 +3505,34 @@ static struct instruction *next_insn_to_validate(struct objtool_file *file, 
	return next_insn_same_sec(file, alt_group->orig_group->last_insn);

}



static bool skip_alt_group(struct instruction *insn)

{

	struct instruction *alt_insn = insn->alts ? insn->alts->insn : NULL;



	/* ANNOTATE_IGNORE_ALTERNATIVE */

	if (insn->alt_group && insn->alt_group->ignore)

		return true;



	/*

	 * For NOP patched with CLAC/STAC, only follow the latter to avoid

	 * impossible code paths combining patched CLAC with unpatched STAC

	 * or vice versa.

	 *

	 * ANNOTATE_IGNORE_ALTERNATIVE could have been used here, but Linus

	 * requested not to do that to avoid hurting .s file readability

	 * around CLAC/STAC alternative sites.

	 */



	if (!alt_insn)

		return false;



	/* Don't override ASM_{CLAC,STAC}_UNSAFE */

	if (alt_insn->alt_group && alt_insn->alt_group->ignore)

		return false;



	return alt_insn->type == INSN_CLAC || alt_insn->type == INSN_STAC;

}



/*

 * Follow the branch starting at the given instruction, and recursively follow

 * any other branches (jumps).  Meanwhile, track the frame pointer state at
@@ -3625,7 +3653,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func, 
			}

		}



		if (insn->alt_group && insn->alt_group->ignore)

		if (skip_alt_group(insn))

			return 0;



		if (handle_insn_ops(insn, next_insn, &state))