linux-kernel - Re: [lkp-robot] [x86/asm] 51bad67ffb: int3:#[##]

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Date:   Wed, 16 May 2018 00:26:45 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
cc:     Alexey Dobriyan <adobriyan@...il.com>,
        "Anvin, H Peter" <h.peter.anvin@...el.com>,
        "Ye, Xiaolong" <xiaolong.ye@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "tipbuild@...or.com" <tipbuild@...or.com>,
        "lkp@...org" <lkp@...org>
Subject: Re: [lkp-robot] [x86/asm] 51bad67ffb: int3:#[##]

On Tue, 15 May 2018, Josh Poimboeuf wrote:
> On Wed, May 16, 2018 at 12:43:37AM +0300, Alexey Dobriyan wrote:
> > On Tue, May 15, 2018 at 09:25:53PM +0000, Anvin, H Peter wrote:
> > > Why is that a problem?
> > > Code: 00 00 00 eb e6 cc cc cc cc cc cc cc cc cc cc cc cc cc fa 8d b6 00 00 00 00 e8 5d e8 8f ff 8b 44 24 34 83 e0 03 83 f8 03 72 28 cc &lt;cc&gt; cc cc cc cc cc cc fa 8d b6 00 00 00 00 e8 3d e8 8f ff 89 e0
> > > 
> > > EIP: ret_from_intr+0xd/0x14 SS:ESP: 0068:8603bfb4
> > > 
> > > INT3 slipped through M586 =&gt; X86_ALIGNMENT_16 :-\
> > 
> > I could make the patch x86_64 only, but!
> > 
> > It crashed into the middle of the padding.
> > 
> > 796ef8fc <ret_from_intr>:
> > 796ef8fc:       8b 44 24 34             mov    eax,DWORD PTR [esp+0x34]
> > 796ef900:       83 e0 03                and    eax,0x3
> > 796ef903:       83 f8 03                cmp    eax,0x3
> > 796ef906:       72 28                   jb     796ef930 <resume_kernel>
> > 796ef908:       cc                      int3
> > 796ef909:       cc       <========>     int3
> > 796ef90a:       cc                      int3
> > 796ef90b:       cc                      int3
> > 796ef90c:       cc                      int3
> > 796ef90d:       cc                      int3
> > 796ef90e:       cc                      int3
> > 796ef90f:       cc                      int3
> 
> The padding isn't needed there, and the resume_userspace symbol is never
> used, so wouldn't this fix it?

Gack. Right you are. I assumed that the ENTRY() is used without checking ....

> 
> diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
> index bef8e2b202a8..9e56243c984c 100644
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -338,7 +338,6 @@ ret_from_intr:
>  	cmpl	$USER_RPL, %eax
>  	jb	resume_kernel			# not returning to v8086 or userspace
>  
> -ENTRY(resume_userspace)
>  	DISABLE_INTERRUPTS(CLBR_ANY)
>  	TRACE_IRQS_OFF
>  	movl	%esp, %eax
>