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

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Thu, May 17, 2018 at 08:49:34AM -0500, Josh Poimboeuf 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(-)
> >
> > 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:
>
> As noted on IRC; I got slightly confused what this was about.
>
> Other than that:
>
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

And after talking to you on IRC I added this paragraph to the changelog:

Also remove incorrect and unnecessary unwinder hints from head_64.S
which caused false positives in the new detection code.

Thanks,

Ingo

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