5 files changed, 93 insertions, 3 deletions

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 47cddf32aeba..53d862aee335 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -264,6 +264,10 @@ objtool_args += --no-unreachable
 else
 objtool_args += $(call cc-ifversion, -lt, 0405, --no-unreachable)
 endif
+ifdef CONFIG_RETPOLINE
+  objtool_args += --retpoline
+endif
+
 
 ifdef CONFIG_MODVERSIONS
 objtool_o = $(@D)/.tmp_$(@F)
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 8d0986d2a803..dd6bcd6097f5 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -29,7 +29,7 @@
 #include "builtin.h"
 #include "check.h"
 
-bool no_fp, no_unreachable;
+bool no_fp, no_unreachable, retpoline;
 
 static const char * const check_usage[] = {
         "objtool check [<options>] file.o",
@@ -39,6 +39,7 @@ static const char * const check_usage[] = {
 const struct option check_options[] = {
         OPT_BOOLEAN('f', "no-fp", &no_fp, "Skip frame pointer validation"),
         OPT_BOOLEAN('u', "no-unreachable", &no_unreachable, "Skip 'unreachable instruction' warnings"),
+        OPT_BOOLEAN('r', "retpoline", &retpoline, "Validate retpoline assumptions"),
         OPT_END(),
 };
 
diff --git a/tools/objtool/builtin.h b/tools/objtool/builtin.h
index f166ea1b1da2..7b6addfce045 100644
--- a/tools/objtool/builtin.h
+++ b/tools/objtool/builtin.h
@@ -20,7 +20,7 @@
 #include <subcmd/parse-options.h>
 
 extern const struct option check_options[];
-extern bool no_fp, no_unreachable;
+extern bool no_fp, no_unreachable, retpoline;
 
 extern int cmd_check(int argc, const char **argv);
 extern int cmd_orc(int argc, const char **argv);
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index ab6f0de7f90d..5e5db7b4d77b 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -497,6 +497,7 @@ static int add_jump_destinations(struct objtool_file *file)
                          * disguise, so convert them accordingly.
                          */
                         insn->type = INSN_JUMP_DYNAMIC;
+                        insn->retpoline_safe = true;
                         continue;
                 } else {
                         /* sibling call */
@@ -548,7 +549,8 @@ static int add_call_destinations(struct objtool_file *file)
                         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.");
+                                if (retpoline)
+                                        WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
                                 return -1;
                         }
 
@@ -1108,6 +1110,54 @@ static int read_unwind_hints(struct objtool_file *file)
         return 0;
 }
 
+static int read_retpoline_hints(struct objtool_file *file)
+{
+        struct section *sec, *relasec;
+        struct instruction *insn;
+        struct rela *rela;
+        int i;
+
+        sec = find_section_by_name(file->elf, ".discard.retpoline_safe");
+        if (!sec)
+                return 0;
+
+        relasec = sec->rela;
+        if (!relasec) {
+                WARN("missing .rela.discard.retpoline_safe section");
+                return -1;
+        }
+
+        if (sec->len % sizeof(unsigned long)) {
+                WARN("retpoline_safe size mismatch: %d %ld", sec->len, sizeof(unsigned long));
+                return -1;
+        }
+
+        for (i = 0; i < sec->len / sizeof(unsigned long); i++) {
+                rela = find_rela_by_dest(sec, i * sizeof(unsigned long));
+                if (!rela) {
+                        WARN("can't find rela for retpoline_safe[%d]", i);
+                        return -1;
+                }
+
+                insn = find_insn(file, rela->sym->sec, rela->addend);
+                if (!insn) {
+                        WARN("can't find insn for retpoline_safe[%d]", i);
+                        return -1;
+                }
+
+                if (insn->type != INSN_JUMP_DYNAMIC &&
+                    insn->type != INSN_CALL_DYNAMIC) {
+                        WARN_FUNC("retpoline_safe hint not a indirect jump/call",
+                                  insn->sec, insn->offset);
+                        return -1;
+                }
+
+                insn->retpoline_safe = true;
+        }
+
+        return 0;
+}
+
 static int decode_sections(struct objtool_file *file)
 {
         int ret;
@@ -1146,6 +1196,10 @@ static int decode_sections(struct objtool_file *file)
         if (ret)
                 return ret;
 
+        ret = read_retpoline_hints(file);
+        if (ret)
+                return ret;
+
         return 0;
 }
 
@@ -1891,6 +1945,29 @@ static int validate_unwind_hints(struct objtool_file *file)
         return warnings;
 }
 
+static int validate_retpoline(struct objtool_file *file)
+{
+        struct instruction *insn;
+        int warnings = 0;
+
+        for_each_insn(file, insn) {
+                if (insn->type != INSN_JUMP_DYNAMIC &&
+                    insn->type != INSN_CALL_DYNAMIC)
+                        continue;
+
+                if (insn->retpoline_safe)
+                        continue;
+
+                WARN_FUNC("indirect %s found in RETPOLINE build",
+                          insn->sec, insn->offset,
+                          insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
+
+                warnings++;
+        }
+
+        return warnings;
+}
+
 static bool is_kasan_insn(struct instruction *insn)
 {
         return (insn->type == INSN_CALL &&
@@ -2051,6 +2128,13 @@ int check(const char *_objname, bool orc)
         if (list_empty(&file.insn_list))
                 goto out;
 
+        if (retpoline) {
+                ret = validate_retpoline(&file);
+                if (ret < 0)
+                        return ret;
+                warnings += ret;
+        }
+
         ret = validate_functions(&file);
         if (ret < 0)
                 goto out;
diff --git a/tools/objtool/check.h b/tools/objtool/check.h
index 936255ba23db..c6b68fcb926f 100644
--- a/tools/objtool/check.h
+++ b/tools/objtool/check.h
@@ -45,6 +45,7 @@ struct instruction {
         unsigned char type;
         unsigned long immediate;
         bool alt_group, visited, dead_end, ignore, hint, save, restore, ignore_alts;
+        bool retpoline_safe;
         struct symbol *call_dest;
         struct instruction *jump_dest;
         struct instruction *first_jump_src;