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

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Message-ID: <20180517140118.GT12217@hirez.programming.kicks-ass.net>
Date:   Thu, 17 May 2018 16:01:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Peter Anvin <h.peter.anvin@...el.com>,
        kernel test robot <xiaolong.ye@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Anvin <hpa@...or.com>, tipbuild@...or.com,
        LKP <lkp@...org>
Subject: Re: [PATCH] objtool: Detect assembly code falling through to INT3
 padding

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@...utronix.de>
> Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.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@...radead.org>