[PATCH V3 5/9] objtool: Add return address unwind hints

[Alexandre Chartre]

Add the UNWIND_HINT_RADDR_DELETE and UNWIND_HINT_RADDR_ALTER unwind
hint macros to flag instructions which remove or modify return
addresses.

Signed-off-by: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
---
 arch/x86/include/asm/orc_types.h       |  2 +
 arch/x86/include/asm/unwind_hints.h    | 23 +++++++++
 tools/arch/x86/include/asm/orc_types.h |  2 +
 tools/objtool/check.c                  | 67 ++++++++++++++++++++++++++
 4 files changed, 94 insertions(+)

diff --git a/arch/x86/include/asm/orc_types.h b/arch/x86/include/asm/orc_types.h
index 6e060907c163..5c1141175d51 100644
--- a/arch/x86/include/asm/orc_types.h
+++ b/arch/x86/include/asm/orc_types.h
@@ -60,6 +60,8 @@
 #define ORC_TYPE_REGS_IRET		2
 #define UNWIND_HINT_TYPE_SAVE		3
 #define UNWIND_HINT_TYPE_RESTORE	4
+#define UNWIND_HINT_TYPE_RADDR_ALTER	6
+#define UNWIND_HINT_TYPE_RADDR_DELETE	7
 
 #ifndef __ASSEMBLY__
 /*
diff --git a/arch/x86/include/asm/unwind_hints.h b/arch/x86/include/asm/unwind_hints.h
index f5e2eb12cb71..5211d2c5b7a2 100644
--- a/arch/x86/include/asm/unwind_hints.h
+++ b/arch/x86/include/asm/unwind_hints.h
@@ -94,6 +94,23 @@
 	UNWIND_HINT type=UNWIND_HINT_TYPE_RESTORE
 .endm
 
+/*
+ * RADDR_DELETE: Used on instructions (other than ret instruction)
+ * which remove a return address from the stack. count is the number
+ * of return address which are removed.
+ */
+.macro UNWIND_HINT_RADDR_DELETE count=1
+	UNWIND_HINT type=UNWIND_HINT_TYPE_RADDR_DELETE sp_offset=\count
+.endm
+
+/*
+ * RADDR_ALTER: Used on instructions which change a return address on
+ * the stack. count is the number of return address which are changed.
+ */
+.macro UNWIND_HINT_RADDR_ALTER count=1
+	UNWIND_HINT type=UNWIND_HINT_TYPE_RADDR_ALTER sp_offset=\count
+.endm
+
 #else /* !__ASSEMBLY__ */
 
 #define UNWIND_HINT(sp_reg, sp_offset, type, end)		\
@@ -112,6 +129,12 @@
 
 #define UNWIND_HINT_RESTORE UNWIND_HINT(0, 0, UNWIND_HINT_TYPE_RESTORE, 0)
 
+#define UNWIND_HINT_RADDR_ALTER(count)	\
+	UNWIND_HINT(0, count, UNWIND_HINT_TYPE_RADDR_ALTER, 0)
+
+#define UNWIND_HINT_RADDR_DELETE(count)	\
+	UNWIND_HINT(0, count, UNWIND_HINT_TYPE_RADDR_DELETE, 0)
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_X86_UNWIND_HINTS_H */
diff --git a/tools/arch/x86/include/asm/orc_types.h b/tools/arch/x86/include/asm/orc_types.h
index 6e060907c163..5c1141175d51 100644
--- a/tools/arch/x86/include/asm/orc_types.h
+++ b/tools/arch/x86/include/asm/orc_types.h
@@ -60,6 +60,8 @@
 #define ORC_TYPE_REGS_IRET		2
 #define UNWIND_HINT_TYPE_SAVE		3
 #define UNWIND_HINT_TYPE_RESTORE	4
+#define UNWIND_HINT_TYPE_RADDR_ALTER	6
+#define UNWIND_HINT_TYPE_RADDR_DELETE	7
 
 #ifndef __ASSEMBLY__
 /*
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8b1df659cd68..0574ce8e232d 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -66,6 +66,28 @@ static bool raddr_pop(struct instruction **insn)
 	return true;
 }
 
+static bool raddr_delete(int count)
+{
+	if (raddr_count < count)
+		return false;
+
+	raddr_count -= count;
+	return true;
+}
+
+static bool raddr_alter(int count)
+{
+	int i;
+
+	if (raddr_count < count)
+		false;
+
+	for (i = 0; i < count; i++)
+		raddr_list[raddr_count - 1 - i] = RADDR_ALTERED;
+
+	return true;
+}
+
 static int validate_branch(struct objtool_file *file, struct symbol *func,
 			   struct instruction *from,
 			   struct instruction *first, struct insn_state state);
@@ -1314,6 +1336,14 @@ static int read_unwind_hints(struct objtool_file *file)
 			insn->restore = true;
 			insn->hint = true;
 			continue;
+
+		} else if (hint->type == UNWIND_HINT_TYPE_RADDR_DELETE) {
+			insn->raddr_delete = hint->sp_offset;
+			continue;
+
+		} else if (hint->type == UNWIND_HINT_TYPE_RADDR_ALTER) {
+			insn->raddr_alter = hint->sp_offset;
+			continue;
 		}
 
 		insn->hint = true;
@@ -1526,6 +1556,13 @@ static bool has_modified_stack_frame(struct insn_state *state)
 	    state->drap)
 		return true;
 
+	/*
+	 * If the stack was altered then don't check registers because
+	 * a callee-saved registers might have been pushed on the stack.
+	 */
+	if (state->stack_altered)
+		return false;
+
 	for (i = 0; i < CFI_NUM_REGS; i++)
 		if (state->regs[i].base != initial_func_cfi.regs[i].base ||
 		    state->regs[i].offset != initial_func_cfi.regs[i].offset)
@@ -2103,6 +2140,15 @@ static int validate_return_address(struct objtool_file *file,
 		if (!raddr_insn)
 			break;
 
+		/*
+		 * If this is a dynamic branch then we expect this
+		 * branch to return or not, depending on the defined
+		 * list of RA we have, so just continue the processing
+		 * of the RA list.
+		 */
+		if (raddr_insn == RADDR_ALTERED)
+			continue;
+
 		/*
 		 * If we are branching to a defined address then
 		 * just do an unconditional jump there.
@@ -2287,6 +2333,27 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 				return 0;
 		}
 
+		if (insn->raddr_delete) {
+			/* delete return address */
+			if (!raddr_delete(insn->raddr_delete)) {
+				WARN_FUNC("fail to delete %d return address",
+					  insn->sec, insn->offset,
+					  insn->raddr_delete);
+				return 1;
+			}
+			state.stack_altered = true;
+
+		} else if (insn->raddr_alter) {
+			/* alter return address */
+			if (!raddr_alter(insn->raddr_alter)) {
+				WARN_FUNC("fail to alter %d return address",
+					  insn->sec, insn->offset,
+					  insn->raddr_alter);
+				return 1;
+			}
+			state.stack_altered = true;
+		}
+
 		switch (insn->type) {
 
 		case INSN_RETURN:
-- 
2.18.2