Commit eda3dc90 authored by Julien Thierry's avatar Julien Thierry Committed by Josh Poimboeuf
Browse files

objtool: Abstract alternative special case handling 



Some alternatives associated with a specific feature need to be treated
in a special way. Since the features and how to treat them vary from one
architecture to another, move the special case handling to arch specific
code.

Reviewed-by: default avatarMiroslav Benes <mbenes@suse.cz>
Signed-off-by: default avatarJulien Thierry <jthierry@redhat.com>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
parent c8ea0d67

tools/objtool/arch/x86/Build

+1 −0
Original line number Diff line number Diff line 
objtool-y += special.o

objtool-y += decode.o



inat_tables_script = ../arch/x86/tools/gen-insn-attr-x86.awk

tools/objtool/arch/x86/special.c

0 → 100644
+37 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0-or-later

#include "../../special.h"

#include "../../builtin.h"



#define X86_FEATURE_POPCNT (4 * 32 + 23)

#define X86_FEATURE_SMAP   (9 * 32 + 20)



void arch_handle_alternative(unsigned short feature, struct special_alt *alt)

{

	switch (feature) {

	case X86_FEATURE_SMAP:

		/*

		 * If UACCESS validation is enabled; force that alternative;

		 * otherwise force it the other way.

		 *

		 * What we want to avoid is having both the original and the

		 * alternative code flow at the same time, in that case we can

		 * find paths that see the STAC but take the NOP instead of

		 * CLAC and the other way around.

		 */

		if (uaccess)

			alt->skip_orig = true;

		else

			alt->skip_alt = true;

		break;

	case X86_FEATURE_POPCNT:

		/*

		 * It has been requested that we don't validate the !POPCNT

		 * feature path which is a "very very small percentage of

		 * machines".

		 */

		alt->skip_orig = true;

		break;

	default:

		break;

	}

}

tools/objtool/objtool.h

+2 −0
Original line number Diff line number Diff line
@@ -12,6 +12,8 @@ 


#include "elf.h"



#define __weak __attribute__((weak))



struct objtool_file {

	struct elf *elf;

	struct list_head insn_list;

tools/objtool/special.c

+5 −27
Original line number Diff line number Diff line
@@ -16,9 +16,6 @@ 
#include "warn.h"

#include "arch_special.h"



#define X86_FEATURE_POPCNT (4*32+23)

#define X86_FEATURE_SMAP   (9*32+20)



struct special_entry {

	const char *sec;

	bool group, jump_or_nop;
@@ -54,6 +51,10 @@ struct special_entry entries[] = { 
	{},

};



void __weak arch_handle_alternative(unsigned short feature, struct special_alt *alt)

{

}



static int get_alt_entry(struct elf *elf, struct special_entry *entry,

			 struct section *sec, int idx,

			 struct special_alt *alt)
@@ -78,30 +79,7 @@ static int get_alt_entry(struct elf *elf, struct special_entry *entry, 


		feature = *(unsigned short *)(sec->data->d_buf + offset +

					      entry->feature);



		/*

		 * It has been requested that we don't validate the !POPCNT

		 * feature path which is a "very very small percentage of

		 * machines".

		 */

		if (feature == X86_FEATURE_POPCNT)

			alt->skip_orig = true;



		/*

		 * If UACCESS validation is enabled; force that alternative;

		 * otherwise force it the other way.

		 *

		 * What we want to avoid is having both the original and the

		 * alternative code flow at the same time, in that case we can

		 * find paths that see the STAC but take the NOP instead of

		 * CLAC and the other way around.

		 */

		if (feature == X86_FEATURE_SMAP) {

			if (uaccess)

				alt->skip_orig = true;

			else

				alt->skip_alt = true;

		}

		arch_handle_alternative(feature, alt);

	}



	orig_reloc = find_reloc_by_dest(elf, sec, offset + entry->orig);

tools/objtool/special.h

+2 −0
Original line number Diff line number Diff line
@@ -28,4 +28,6 @@ struct special_alt { 


int special_get_alts(struct elf *elf, struct list_head *alts);



void arch_handle_alternative(unsigned short feature, struct special_alt *alt);



#endif /* _SPECIAL_H */

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