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Subject[PATCH 1/4] objtool: Improve retpoline alternative handling
Date
Currently objtool requires all retpolines to be

a) patched in with alternatives; and

b) annotated with ANNOTATE_NOSPEC_ALTERNATIVE.

If you forget to do both of the above, objtool seg faults trying to
dereference a NULL 'insn->call_dest' pointer.

Avoid that situation and print a more helpful error message:

quirks.o: warning: objtool: efi_delete_dummy_variable()+0x99: unsupported intra-function call
quirks.o: warning: objtool: If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.

Future improvements can be made to make objtool smarter with respect to
retpolines, but this is a good incremental improvement for now.

Reported-and-tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
tools/objtool/check.c | 36 ++++++++++++++++--------------------
1 file changed, 16 insertions(+), 20 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index f40d46e24bcc..bc3490d929ff 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -543,18 +543,14 @@ static int add_call_destinations(struct objtool_file *file)
dest_off = insn->offset + insn->len + insn->immediate;
insn->call_dest = find_symbol_by_offset(insn->sec,
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) {
- WARN_FUNC("can't find call dest symbol at offset 0x%lx",
- insn->sec, insn->offset, dest_off);
+
+ if (!insn->call_dest && !insn->ignore) {
+ WARN_FUNC("unsupported intra-function call",
+ insn->sec, insn->offset);
+ WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
return -1;
}
-#endif
+
} else if (rela->sym->type == STT_SECTION) {
insn->call_dest = find_symbol_by_offset(rela->sym->sec,
rela->addend+4);
@@ -648,6 +644,8 @@ static int handle_group_alt(struct objtool_file *file,

last_new_insn = insn;

+ insn->ignore = orig_insn->ignore_alts;
+
if (insn->type != INSN_JUMP_CONDITIONAL &&
insn->type != INSN_JUMP_UNCONDITIONAL)
continue;
@@ -729,10 +727,6 @@ static int add_special_section_alts(struct objtool_file *file)
goto out;
}

- /* Ignore retpoline alternatives. */
- if (orig_insn->ignore_alts)
- continue;
-
new_insn = NULL;
if (!special_alt->group || special_alt->new_len) {
new_insn = find_insn(file, special_alt->new_sec,
@@ -1089,11 +1083,11 @@ static int decode_sections(struct objtool_file *file)
if (ret)
return ret;

- ret = add_call_destinations(file);
+ ret = add_special_section_alts(file);
if (ret)
return ret;

- ret = add_special_section_alts(file);
+ ret = add_call_destinations(file);
if (ret)
return ret;

@@ -1720,10 +1714,12 @@ static int validate_branch(struct objtool_file *file, struct instruction *first,

insn->visited = true;

- list_for_each_entry(alt, &insn->alts, list) {
- ret = validate_branch(file, alt->insn, state);
- if (ret)
- return 1;
+ if (!insn->ignore_alts) {
+ list_for_each_entry(alt, &insn->alts, list) {
+ ret = validate_branch(file, alt->insn, state);
+ if (ret)
+ return 1;
+ }
}

switch (insn->type) {
--
2.14.3
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