45245f51f9
As pointed out by the comment in handle_group_alt(), support of relocation for instructions in an alternative group depends on whether arch specific kernel code handles it. So, let objtool arch specific code decide whether a relocation for the alternative section should be accepted. Reviewed-by: Miroslav Benes <mbenes@suse.cz> Signed-off-by: Julien Thierry <jthierry@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
51 lines
1.3 KiB
C
51 lines
1.3 KiB
C
// 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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}
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bool arch_support_alt_relocation(struct special_alt *special_alt,
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struct instruction *insn,
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struct reloc *reloc)
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{
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/*
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* The x86 alternatives code adjusts the offsets only when it
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* encounters a branch instruction at the very beginning of the
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* replacement group.
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*/
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return insn->offset == special_alt->new_off &&
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(insn->type == INSN_CALL || is_static_jump(insn));
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}
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