Re: [PATCH] objtool: Detect assembly code falling through to INT3 padding

[Ingo Molnar]

* Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:

> With the following commit:
> 
>   51bad67ffbce ("x86/asm: Pad assembly functions with INT3 instructions")
> 
> ... asm function alignments are padded with INT3, so it's no longer safe
> to fall through to an aligned function.  Make sure we catch any such
> cases with objtool.
> 
> Note this only adds checking for 64-bit, since objtool doesn't support
> x86-32.
> 
> Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> ---
>  arch/x86/kernel/head_64.S       |  2 --
>  tools/objtool/arch.h            |  3 ++-
>  tools/objtool/arch/x86/decode.c |  2 +-
>  tools/objtool/check.c           | 11 ++++++++++-
>  4 files changed, 13 insertions(+), 5 deletions(-)

Ok, this is cool, it addresses the robustness problem that INT3 padding introduced 
very nicely.

The concept of built-in kernel tooling working at the machine code level is just 
so powerful - we should have added our own KCC compiler 20 years ago.

Thanks,

	Ingo