[PATCH v3 2/3] objtool: Add support for intra-function calls

[Rui Qi]

From: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>

commit 8aa8eb2a8f5b3305a95f39957dd2b715fa668e21 upstream.

Change objtool to support intra-function calls. On x86, an intra-function
call is represented in objtool as a push onto the stack (of the return
address), and a jump to the destination address. That way the stack
information is correctly updated and the call flow is still accurate.

Signed-off-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Miroslav Benes <mbenes@xxxxxxx>
Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200414103618.12657-4-alexandre.chartre@xxxxxxxxxx
Signed-off-by: Rui Qi <qirui.001@xxxxxxxxxxxxx>
---
 include/linux/frame.h                         | 11 ++++
 .../Documentation/stack-validation.txt        |  8 +++
 tools/objtool/arch/x86/decode.c               |  6 ++
 tools/objtool/check.c                         | 62 +++++++++++++++++--
 4 files changed, 83 insertions(+), 4 deletions(-)

diff --git a/include/linux/frame.h b/include/linux/frame.h
index 02d3ca2d9598..303cda600e56 100644
--- a/include/linux/frame.h
+++ b/include/linux/frame.h
@@ -15,9 +15,20 @@
 	static void __used __section(.discard.func_stack_frame_non_standard) \
 		*__func_stack_frame_non_standard_##func = func
 
+/*
+ * This macro indicates that the following intra-function call is valid.
+ * Any non-annotated intra-function call will cause objtool to issue a warning.
+ */
+#define ANNOTATE_INTRA_FUNCTION_CALL				\
+	999:							\
+	.pushsection .discard.intra_function_calls;		\
+	.long 999b;						\
+	.popsection;
+
 #else /* !CONFIG_STACK_VALIDATION */
 
 #define STACK_FRAME_NON_STANDARD(func)
+#define ANNOTATE_INTRA_FUNCTION_CALL
 
 #endif /* CONFIG_STACK_VALIDATION */
 
diff --git a/tools/objtool/Documentation/stack-validation.txt b/tools/objtool/Documentation/stack-validation.txt
index de094670050b..ee26bb382b70 100644
--- a/tools/objtool/Documentation/stack-validation.txt
+++ b/tools/objtool/Documentation/stack-validation.txt
@@ -290,6 +290,14 @@ they mean, and suggestions for how to fix them.
       https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646
 
 
+11. file.o: warning: unannotated intra-function call
+
+   This warning means that a direct call is done to a destination which
+   is not at the beginning of a function. If this is a legit call, you
+   can remove this warning by putting the ANNOTATE_INTRA_FUNCTION_CALL
+   directive right before the call.
+
+
 If the error doesn't seem to make sense, it could be a bug in objtool.
 Feel free to ask the objtool maintainer for help.
 
diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index a62e032863a8..c3ff62c085c8 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -437,6 +437,12 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
 
 	case 0xe8:
 		*type = INSN_CALL;
+		/*
+		 * For the impact on the stack, a CALL behaves like
+		 * a PUSH of an immediate value (the return address).
+		 */
+			op->src.type = OP_SRC_CONST;
+			op->dest.type = OP_DEST_PUSH;
 		break;
 
 	case 0xfc:
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 71a24fd46dbd..0fa414869f45 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -645,6 +645,7 @@ static int add_jump_destinations(struct objtool_file *file)
 	return 0;
 }
 
+
 /*
  * Find the destination instructions for all calls.
  */
@@ -666,10 +667,7 @@ static int add_call_destinations(struct objtool_file *file)
 								dest_off);
 
 			if (!insn->call_dest && !insn->ignore) {
-				WARN_FUNC("unsupported intra-function call",
-					  insn->sec, insn->offset);
-				if (retpoline)
-					WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
+				WARN_FUNC("unannotated intra-function call", insn->sec, insn->offset);
 				return -1;
 			}
 
@@ -1291,6 +1289,58 @@ static int read_retpoline_hints(struct objtool_file *file)
 	return 0;
 }
 
+
+static int read_intra_function_calls(struct objtool_file *file)
+{
+	struct instruction *insn;
+	struct section *sec;
+	struct rela *rela;
+
+	sec = find_section_by_name(file->elf, ".rela.discard.intra_function_calls");
+	if (!sec)
+		return 0;
+
+	list_for_each_entry(rela, &sec->rela_list, list) {
+		unsigned long dest_off;
+
+		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.intra_function_call entry");
+			return -1;
+		}
+
+		if (insn->type != INSN_CALL) {
+			WARN_FUNC("intra_function_call not a direct call",
+				  insn->sec, insn->offset);
+			return -1;
+		}
+
+		/*
+		 * Treat intra-function CALLs as JMPs, but with a stack_op.
+		 * See add_call_destinations(), which strips stack_ops from
+		 * normal CALLs.
+		 */
+		insn->type = INSN_JUMP_UNCONDITIONAL;
+
+		dest_off = insn->offset + insn->len + insn->immediate;
+		insn->jump_dest = find_insn(file, insn->sec, dest_off);
+		if (!insn->jump_dest) {
+			WARN_FUNC("can't find call dest at %s+0x%lx",
+				  insn->sec, insn->offset,
+				  insn->sec->name, dest_off);
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
 static void mark_rodata(struct objtool_file *file)
 {
 	struct section *sec;
@@ -1346,6 +1396,10 @@ static int decode_sections(struct objtool_file *file)
 	if (ret)
 		return ret;
 
+	ret = read_intra_function_calls(file);
+	if (ret)
+		return ret;
+
 	ret = add_call_destinations(file);
 	if (ret)
 		return ret;
-- 
2.20.1