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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: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Julien Thierry <jthierry@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
authored by
Julien Thierry
and committed by
Josh Poimboeuf
eda3dc90
c8ea0d67
+47
-29
+1
tools/objtool/arch/x86/Build
+1
tools/objtool/arch/x86/Build
+37
tools/objtool/arch/x86/special.c
+37
tools/objtool/arch/x86/special.c
···
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// SPDX-License-Identifier: GPL-2.0-or-later
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#include "../../special.h"
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#include "../../builtin.h"
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#define X86_FEATURE_POPCNT (4 * 32 + 23)
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#define X86_FEATURE_SMAP (9 * 32 + 20)
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void arch_handle_alternative(unsigned short feature, struct special_alt *alt)
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{
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switch (feature) {
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case X86_FEATURE_SMAP:
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/*
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* If UACCESS validation is enabled; force that alternative;
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* otherwise force it the other way.
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*
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* What we want to avoid is having both the original and the
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* alternative code flow at the same time, in that case we can
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* find paths that see the STAC but take the NOP instead of
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* CLAC and the other way around.
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*/
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if (uaccess)
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alt->skip_orig = true;
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else
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alt->skip_alt = true;
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break;
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case X86_FEATURE_POPCNT:
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/*
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* It has been requested that we don't validate the !POPCNT
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* feature path which is a "very very small percentage of
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* machines".
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*/
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alt->skip_orig = true;
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break;
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default:
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break;
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}
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}
+2
tools/objtool/objtool.h
+2
tools/objtool/objtool.h
+5
-27
tools/objtool/special.c
+5
-27
tools/objtool/special.c
···
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#include "warn.h"
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#include "arch_special.h"
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#define X86_FEATURE_POPCNT (4*32+23)
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#define X86_FEATURE_SMAP (9*32+20)
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-
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struct special_entry {
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const char *sec;
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bool group, jump_or_nop;
···
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{},
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};
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void __weak arch_handle_alternative(unsigned short feature, struct special_alt *alt)
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{
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}
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static int get_alt_entry(struct elf *elf, struct special_entry *entry,
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struct section *sec, int idx,
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struct special_alt *alt)
···
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feature = *(unsigned short *)(sec->data->d_buf + offset +
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entry->feature);
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-
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/*
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* It has been requested that we don't validate the !POPCNT
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* feature path which is a "very very small percentage of
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* machines".
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*/
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if (feature == X86_FEATURE_POPCNT)
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alt->skip_orig = true;
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/*
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* If UACCESS validation is enabled; force that alternative;
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* otherwise force it the other way.
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*
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* What we want to avoid is having both the original and the
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* alternative code flow at the same time, in that case we can
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* find paths that see the STAC but take the NOP instead of
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* CLAC and the other way around.
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*/
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if (feature == X86_FEATURE_SMAP) {
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if (uaccess)
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alt->skip_orig = true;
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else
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alt->skip_alt = true;
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}
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arch_handle_alternative(feature, alt);
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}
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orig_reloc = find_reloc_by_dest(elf, sec, offset + entry->orig);
+2
tools/objtool/special.h
+2
tools/objtool/special.h