On Tue, May 15, 2018 at 04:05:33PM -0700, Linus Torvalds wrote:
> I wonder if there's some way to add a test for "ENTRY only works in a code
> section"?
I suppose we could add a discardable annotation to the ENTRY macro and
have objtool validate that it's in a text section. I'm not sure whether
it's worth it, but I could do it if you think it's a good idea.
Below is a tentative objtool patch which catches asm code falling
through to INT3 padding, though objtool is 64-bit only so there won't be
any 32-bit coverage. It found zero hits on my config. I'll clean it up
and submit it tomorrow-ish.
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 8344dd2f310a..3ed8cec6e765 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -285,11 +285,9 @@ ENTRY(early_idt_handler_array)
.endif
pushq $i # 72(%rsp) Vector number
jmp early_idt_handler_common
- UNWIND_HINT_IRET_REGS
i = i + 1
.fill early_idt_handler_array + i*EARLY_IDT_HANDLER_SIZE - ., 1, 0xcc
.endr
- UNWIND_HINT_IRET_REGS offset=16
END(early_idt_handler_array)
early_idt_handler_common:
diff --git a/tools/objtool/arch.h b/tools/objtool/arch.h
index b0d7dc3d71b5..6eb058a8ac00 100644
--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h
@@ -33,7 +33,8 @@
#define INSN_STACK 8
#define INSN_BUG 9
#define INSN_NOP 10
-#define INSN_OTHER 11
+#define INSN_PADDING 11
+#define INSN_OTHER 12
#define INSN_LAST INSN_OTHER
enum op_dest_type {
diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 7e86a743f851..82b41bb93c02 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -421,7 +421,7 @@ int arch_decode_instruction(struct elf *elf, struct section
*sec,
case 0xcc:
/* int3: used for asm function padding by the __ALIGN macro */
- *type = INSN_NOP;
+ *type = INSN_PADDING;
break;
case 0xe3:
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index f4bbce838433..8a83a0d1693a 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1936,6 +1936,14 @@ static int validate_branch(struct objtool_file *file,
struct instruction *first,
}
return 0;
+ case INSN_PADDING:
+ if (!func) {
+ WARN_FUNC("code falls through to INT3 padding",
+ insn->sec, insn->offset);
+ return 1;
+ }
+ break;
+
case INSN_STACK:
if (update_insn_state(insn, &state))
return 1;
@@ -2032,7 +2040,8 @@ static bool ignore_unreachable_insn(struct instruction
*insn)
{
int i;
- if (insn->ignore || insn->type == INSN_NOP)
+ if (insn->ignore || insn->type == INSN_NOP ||
+ insn->type == INSN_PADDING)
return true;
/*
