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

* Ingo Molnar <mingo@kernel.org> wrote:

>
> * Josh Poimboeuf <jpoimboe@redhat.com> 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@linutronix.de>
> > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> > ---
> > 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.

Hm, so a problem is that if we change the padding on 32-bit as well we won't have
this detection there, because objtool doesn't work on 32-bit.

Thanks,

Ingo

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