objtool: Revert "skip non-text sections when adding return-thunk sites"

JIRA: https://issues.redhat.com/browse/RHEL-71467
Upstream Status: RHEL only

The RHEL only commit d0fd1f5 ("objtool: skip non-text sections when
adding return-thunk sites") is based on a linux stable commit like the
linux-5.18.y's commit f7b097e ("objtool: skip non-text sections
when adding return-thunk sites") to work around an x86 linking problem
at the time.

Now the linking problem doesn't seem to be present anymore with the
latest RHEL9 source code. It is time to revert the commit as it is
causing objtool to ignore return sites in .altinstr_replacement created
by the ALTERNATIVE* macros. So these return sites never gets added to
.return.sites and thus doesn't get patched by apply_returns(). This is
bad as they can be potential security holes even if RETBleed mitigation
has been enabled. Thank Josh Poimboeuf for figuring out this bug.

Signed-off-by: Waiman Long <longman@redhat.com>

Author: Waiman-Long

tools/objtool/check.c

@@ -1458,8 +1458,7 @@ static void add_return_call(struct objtool_file *file, struct instruction *insn,
 	insn->type = INSN_RETURN;
 	insn->retpoline_safe = true;
 
-	/* Skip the non-text sections, specially .discard ones */
-	if (add && insn->sec->text)
+	if (add)
 		list_add_tail(&insn->call_node, &file->return_thunk_list);
 }