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forked fromtorvalds/linux

Commit258c760

Browse files
jpoimboeKAGA-KOKO
authored andcommitted
objtool: Allow alternatives to be ignored
Getting objtool to understand retpolines is going to be a bit of achallenge. For now, take advantage of the fact that retpolines arepatched in with alternatives. Just read the original (sane)non-alternative instruction, and ignore the patched-in retpoline.This allows objtool to understand the control flow *around* theretpoline, even if it can't yet follow what's inside. This means theORC unwinder will fail to unwind from inside a retpoline, but will workfine otherwise.Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>Signed-off-by: Thomas Gleixner <tglx@linutronix.de>Cc: gnomes@lxorguk.ukuu.org.ukCc: Rik van Riel <riel@redhat.com>Cc: Andi Kleen <ak@linux.intel.com>Cc: thomas.lendacky@amd.comCc: Peter Zijlstra <peterz@infradead.org>Cc: Linus Torvalds <torvalds@linux-foundation.org>Cc: Jiri Kosina <jikos@kernel.org>Cc: Andy Lutomirski <luto@amacapital.net>Cc: Dave Hansen <dave.hansen@intel.com>Cc: Kees Cook <keescook@google.com>Cc: Tim Chen <tim.c.chen@linux.intel.com>Cc: Greg Kroah-Hartman <gregkh@linux-foundation.org>Cc: Paul Turner <pjt@google.com>Link:https://lkml.kernel.org/r/1515707194-20531-3-git-send-email-dwmw@amazon.co.uk
1 parent39b7353 commit258c760

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2 files changed

+57
-7
lines changed

2 files changed

+57
-7
lines changed

‎tools/objtool/check.c‎

Lines changed: 56 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -427,6 +427,40 @@ static void add_ignores(struct objtool_file *file)
427427
}
428428
}
429429

430+
/*
431+
* FIXME: For now, just ignore any alternatives which add retpolines. This is
432+
* a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
433+
* But it at least allows objtool to understand the control flow *around* the
434+
* retpoline.
435+
*/
436+
staticintadd_nospec_ignores(structobjtool_file*file)
437+
{
438+
structsection*sec;
439+
structrela*rela;
440+
structinstruction*insn;
441+
442+
sec=find_section_by_name(file->elf,".rela.discard.nospec");
443+
if (!sec)
444+
return0;
445+
446+
list_for_each_entry(rela,&sec->rela_list,list) {
447+
if (rela->sym->type!=STT_SECTION) {
448+
WARN("unexpected relocation symbol type in %s",sec->name);
449+
return-1;
450+
}
451+
452+
insn=find_insn(file,rela->sym->sec,rela->addend);
453+
if (!insn) {
454+
WARN("bad .discard.nospec entry");
455+
return-1;
456+
}
457+
458+
insn->ignore_alts= true;
459+
}
460+
461+
return0;
462+
}
463+
430464
/*
431465
* Find the destination instructions for all jumps.
432466
*/
@@ -509,11 +543,18 @@ static int add_call_destinations(struct objtool_file *file)
509543
dest_off=insn->offset+insn->len+insn->immediate;
510544
insn->call_dest=find_symbol_by_offset(insn->sec,
511545
dest_off);
546+
/*
547+
* FIXME: Thanks to retpolines, it's now considered
548+
* normal for a function to call within itself. So
549+
* disable this warning for now.
550+
*/
551+
#if0
512552
if (!insn->call_dest) {
513553
WARN_FUNC("can't find call dest symbol at offset 0x%lx",
514554
insn->sec,insn->offset,dest_off);
515555
return-1;
516556
}
557+
#endif
517558
}elseif (rela->sym->type==STT_SECTION) {
518559
insn->call_dest=find_symbol_by_offset(rela->sym->sec,
519560
rela->addend+4);
@@ -678,12 +719,6 @@ static int add_special_section_alts(struct objtool_file *file)
678719
returnret;
679720

680721
list_for_each_entry_safe(special_alt,tmp,&special_alts,list) {
681-
alt=malloc(sizeof(*alt));
682-
if (!alt) {
683-
WARN("malloc failed");
684-
ret=-1;
685-
gotoout;
686-
}
687722

688723
orig_insn=find_insn(file,special_alt->orig_sec,
689724
special_alt->orig_off);
@@ -694,6 +729,10 @@ static int add_special_section_alts(struct objtool_file *file)
694729
gotoout;
695730
}
696731

732+
/* Ignore retpoline alternatives. */
733+
if (orig_insn->ignore_alts)
734+
continue;
735+
697736
new_insn=NULL;
698737
if (!special_alt->group||special_alt->new_len) {
699738
new_insn=find_insn(file,special_alt->new_sec,
@@ -719,6 +758,13 @@ static int add_special_section_alts(struct objtool_file *file)
719758
gotoout;
720759
}
721760

761+
alt=malloc(sizeof(*alt));
762+
if (!alt) {
763+
WARN("malloc failed");
764+
ret=-1;
765+
gotoout;
766+
}
767+
722768
alt->insn=new_insn;
723769
list_add_tail(&alt->list,&orig_insn->alts);
724770

@@ -1035,6 +1081,10 @@ static int decode_sections(struct objtool_file *file)
10351081

10361082
add_ignores(file);
10371083

1084+
ret=add_nospec_ignores(file);
1085+
if (ret)
1086+
returnret;
1087+
10381088
ret=add_jump_destinations(file);
10391089
if (ret)
10401090
returnret;

‎tools/objtool/check.h‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -44,7 +44,7 @@ struct instruction {
4444
unsignedintlen;
4545
unsignedchartype;
4646
unsigned longimmediate;
47-
boolalt_group,visited,dead_end,ignore,hint,save,restore;
47+
boolalt_group,visited,dead_end,ignore,hint,save,restore,ignore_alts;
4848
structsymbol*call_dest;
4949
structinstruction*jump_dest;
5050
structlist_headalts;

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