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Patch "objtool: Improve retpoline alternative handling" has been added to the 4.14-stable tree

PATCH [email protected] 1 participant 1 message Feb 5, 2018

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This is a note to let you know that I've just added the patch titled

objtool: Improve retpoline alternative handling

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
objtool_Improve_retpoline_alternative_handling.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Subject: objtool: Improve retpoline alternative handling
From: Josh Poimboeuf [email protected]
Date: Mon Jan 29 22:00:39 2018 -0600

From: Josh Poimboeuf [email protected]

commit a845c7cf4b4cb5e9e3b2823867892b27646f3a98

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 segfaults 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.

---
 tools/objtool/check.c |   36 ++++++++++++++++--------------------
 1 file changed, 16 insertions(+), 20 deletions(-)
tools/objtool/check.c +16 -20
@@ -543,18 +543,14 @@ static int add_call_destinations(struct
 			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 objto
 
 		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(stru
 			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 objtoo
 	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 objtoo
 
 		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) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/objtool_Add_support_for_alternatives_at_the_end_of_a_section.patch queue-4.14/objtool_Warn_on_stripped_section_symbol.patch queue-4.14/objtool_Improve_retpoline_alternative_handling.patch