objtool: Fully validate the stack frame

A valid stack frame should contain both the return address and the
previous frame pointer value.

On x86, the return value is placed on the stack by the calling
instructions. On other architectures, the callee needs to explicitly
save the return address on the stack.

Add the necessary checks to verify a function properly sets up all the
elements of the stack frame.

Signed-off-by: Julien Thierry <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>

1 files changed, 11 insertions, 4 deletions

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 5f8d3eed78a1..88210b0856f7 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1733,12 +1733,20 @@ static bool has_modified_stack_frame(struct instruction *insn, struct insn_state
 	return false;
 }
 
+static bool check_reg_frame_pos(const struct cfi_reg *reg,
+				int expected_offset)
+{
+	return reg->base == CFI_CFA &&
+	       reg->offset == expected_offset;
+}
+
 static bool has_valid_stack_frame(struct insn_state *state)
 {
 	struct cfi_state *cfi = &state->cfi;
 
-	if (cfi->cfa.base == CFI_BP && cfi->regs[CFI_BP].base == CFI_CFA &&
-	    cfi->regs[CFI_BP].offset == -16)
+	if (cfi->cfa.base == CFI_BP &&
+	    check_reg_frame_pos(&cfi->regs[CFI_BP], -cfi->cfa.offset) &&
+	    check_reg_frame_pos(&cfi->regs[CFI_RA], -cfi->cfa.offset + 8))
 		return true;
 
 	if (cfi->drap && cfi->regs[CFI_BP].base == CFI_BP)
@@ -1867,8 +1875,7 @@ static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
 		case OP_SRC_REG:
 			if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
 			    cfa->base == CFI_SP &&
-			    regs[CFI_BP].base == CFI_CFA &&
-			    regs[CFI_BP].offset == -cfa->offset) {
+			    check_reg_frame_pos(&regs[CFI_BP], -cfa->offset)) {
 
 				/* mov %rsp, %rbp */
 				cfa->base = op->dest.reg;