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objtool: Abstract alternative special case handling

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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: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Julien Thierry <jthierry@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
This commit is contained in:
Julien Thierry 2020-09-04 16:30:22 +01:00 committed by Josh Poimboeuf
parent c8ea0d6725
commit eda3dc9058
6 changed files with 47 additions and 29 deletions
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1
tools/objtool/arch/x86/Build
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@ -1,3 +1,4 @@
objtool-y += special.o
objtool-y += decode.o
inat_tables_script = ../arch/x86/tools/gen-insn-attr-x86.awk

37
tools/objtool/arch/x86/special.c Normal file
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@ -0,0 +1,37 @@
// 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;
}
}

2
tools/objtool/objtool.h
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@ -12,6 +12,8 @@
#include "elf.h"
#define __weak __attribute__((weak))
struct objtool_file {
struct elf *elf;
struct list_head insn_list;

32
tools/objtool/special.c
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@ -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);

2
tools/objtool/special.h
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@ -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 */

2
tools/objtool/weak.c
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@ -9,8 +9,6 @@
#include <errno.h>
#include "objtool.h"
#define __weak __attribute__((weak))
#define UNSUPPORTED(name) \
({ \
fprintf(stderr, "error: objtool: " name " not implemented\n"); \