Commit 258c7605 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Thomas Gleixner

objtool: Allow alternatives to be ignored

Getting objtool to understand retpolines is going to be a bit of a
challenge.  For now, take advantage of the fact that retpolines are
patched 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* the
retpoline, even if it can't yet follow what's inside.  This means the
ORC unwinder will fail to unwind from inside a retpoline, but will work
fine otherwise.
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarDavid Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: gnomes@lxorguk.ukuu.org.uk
Cc: Rik van Riel <riel@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: thomas.lendacky@amd.com
Cc: 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
parent 39b73533
...@@ -427,6 +427,40 @@ static void add_ignores(struct objtool_file *file) ...@@ -427,6 +427,40 @@ static void add_ignores(struct objtool_file *file)
} }
} }
/*
* FIXME: For now, just ignore any alternatives which add retpolines. This is
* a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
* But it at least allows objtool to understand the control flow *around* the
* retpoline.
*/
static int add_nospec_ignores(struct objtool_file *file)
{
struct section *sec;
struct rela *rela;
struct instruction *insn;
sec = find_section_by_name(file->elf, ".rela.discard.nospec");
if (!sec)
return 0;
list_for_each_entry(rela, &sec->rela_list, list) {
if (rela->sym->type != STT_SECTION) {
WARN("unexpected relocation symbol type in %s", sec->name);
return -1;
}
insn = find_insn(file, rela->sym->sec, rela->addend);
if (!insn) {
WARN("bad .discard.nospec entry");
return -1;
}
insn->ignore_alts = true;
}
return 0;
}
/* /*
* Find the destination instructions for all jumps. * Find the destination instructions for all jumps.
*/ */
...@@ -509,11 +543,18 @@ static int add_call_destinations(struct objtool_file *file) ...@@ -509,11 +543,18 @@ static int add_call_destinations(struct objtool_file *file)
dest_off = insn->offset + insn->len + insn->immediate; dest_off = insn->offset + insn->len + insn->immediate;
insn->call_dest = find_symbol_by_offset(insn->sec, insn->call_dest = find_symbol_by_offset(insn->sec,
dest_off); dest_off);
/*
* FIXME: Thanks to retpolines, it's now considered
* normal for a function to call within itself. So
* disable this warning for now.
*/
#if 0
if (!insn->call_dest) { if (!insn->call_dest) {
WARN_FUNC("can't find call dest symbol at offset 0x%lx", WARN_FUNC("can't find call dest symbol at offset 0x%lx",
insn->sec, insn->offset, dest_off); insn->sec, insn->offset, dest_off);
return -1; return -1;
} }
#endif
} else if (rela->sym->type == STT_SECTION) { } else if (rela->sym->type == STT_SECTION) {
insn->call_dest = find_symbol_by_offset(rela->sym->sec, insn->call_dest = find_symbol_by_offset(rela->sym->sec,
rela->addend+4); rela->addend+4);
...@@ -678,12 +719,6 @@ static int add_special_section_alts(struct objtool_file *file) ...@@ -678,12 +719,6 @@ static int add_special_section_alts(struct objtool_file *file)
return ret; return ret;
list_for_each_entry_safe(special_alt, tmp, &special_alts, list) { list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
alt = malloc(sizeof(*alt));
if (!alt) {
WARN("malloc failed");
ret = -1;
goto out;
}
orig_insn = find_insn(file, special_alt->orig_sec, orig_insn = find_insn(file, special_alt->orig_sec,
special_alt->orig_off); special_alt->orig_off);
...@@ -694,6 +729,10 @@ static int add_special_section_alts(struct objtool_file *file) ...@@ -694,6 +729,10 @@ static int add_special_section_alts(struct objtool_file *file)
goto out; goto out;
} }
/* Ignore retpoline alternatives. */
if (orig_insn->ignore_alts)
continue;
new_insn = NULL; new_insn = NULL;
if (!special_alt->group || special_alt->new_len) { if (!special_alt->group || special_alt->new_len) {
new_insn = find_insn(file, special_alt->new_sec, new_insn = find_insn(file, special_alt->new_sec,
...@@ -719,6 +758,13 @@ static int add_special_section_alts(struct objtool_file *file) ...@@ -719,6 +758,13 @@ static int add_special_section_alts(struct objtool_file *file)
goto out; goto out;
} }
alt = malloc(sizeof(*alt));
if (!alt) {
WARN("malloc failed");
ret = -1;
goto out;
}
alt->insn = new_insn; alt->insn = new_insn;
list_add_tail(&alt->list, &orig_insn->alts); list_add_tail(&alt->list, &orig_insn->alts);
...@@ -1035,6 +1081,10 @@ static int decode_sections(struct objtool_file *file) ...@@ -1035,6 +1081,10 @@ static int decode_sections(struct objtool_file *file)
add_ignores(file); add_ignores(file);
ret = add_nospec_ignores(file);
if (ret)
return ret;
ret = add_jump_destinations(file); ret = add_jump_destinations(file);
if (ret) if (ret)
return ret; return ret;
......
...@@ -44,7 +44,7 @@ struct instruction { ...@@ -44,7 +44,7 @@ struct instruction {
unsigned int len; unsigned int len;
unsigned char type; unsigned char type;
unsigned long immediate; unsigned long immediate;
bool alt_group, visited, dead_end, ignore, hint, save, restore; bool alt_group, visited, dead_end, ignore, hint, save, restore, ignore_alts;
struct symbol *call_dest; struct symbol *call_dest;
struct instruction *jump_dest; struct instruction *jump_dest;
struct list_head alts; struct list_head alts;
......
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