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From: Thomas Gleixner <tglx@linutronix.de>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: "Anvin, H Peter" <h.peter.anvin@intel.com>,
	"Ye, Xiaolong" <xiaolong.ye@intel.com>,
	Ingo Molnar <mingo@kernel.org>, Andy Lutomirski <luto@kernel.org>,
	Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"tipbuild@zytor.com" <tipbuild@zytor.com>,
	"lkp@01.org" <lkp@01.org>
Subject: Re: [lkp-robot] [x86/asm] 51bad67ffb: int3:#[##]
Date: Wed, 16 May 2018 00:25:46 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1805160009230.1605@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20180515214337.GA18021@avx2>

On Wed, 16 May 2018, 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

EIP points to the second int3 because that's where a simple return would
return to. do_trap() does not handle int3 special.

>From a quick check that seems to be the only code sequence which has:

     jcc     lbl

ENTRY(foo)

and ENTRY() aligns to a 16 byte boundary. So the simple fix for that is
below. We need objtool support to detect such places ...

Thanks,

	tglx

8<-------------------

--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -338,6 +338,11 @@ END(ret_from_fork)
 	cmpl	$USER_RPL, %eax
 	jb	resume_kernel			# not returning to v8086 or userspace
 
+	/*
+	 * Jump over the alignment padding which is filled with int3 instructions
+	 */
+	jmp	resume_userspace
+
 ENTRY(resume_userspace)
 	DISABLE_INTERRUPTS(CLBR_ANY)
 	TRACE_IRQS_OFF

WARNING: multiple messages have this Message-ID (diff)
From: Thomas Gleixner <tglx@linutronix.de>
To: lkp@lists.01.org
Subject: Re: [lkp-robot] [x86/asm] 51bad67ffb: int3:#[##]
Date: Wed, 16 May 2018 00:25:46 +0200	[thread overview]
Message-ID: <alpine.DEB.2.21.1805160009230.1605@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20180515214337.GA18021@avx2>

[-- Attachment #1: Type: text/plain, Size: 1776 bytes --]

On Wed, 16 May 2018, 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

EIP points to the second int3 because that's where a simple return would
return to. do_trap() does not handle int3 special.

>From a quick check that seems to be the only code sequence which has:

     jcc     lbl

ENTRY(foo)

and ENTRY() aligns to a 16 byte boundary. So the simple fix for that is
below. We need objtool support to detect such places ...

Thanks,

	tglx

8<-------------------

--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -338,6 +338,11 @@ END(ret_from_fork)
 	cmpl	$USER_RPL, %eax
 	jb	resume_kernel			# not returning to v8086 or userspace
 
+	/*
+	 * Jump over the alignment padding which is filled with int3 instructions
+	 */
+	jmp	resume_userspace
+
 ENTRY(resume_userspace)
 	DISABLE_INTERRUPTS(CLBR_ANY)
 	TRACE_IRQS_OFF


  parent reply	other threads:[~2018-05-15 22:26 UTC|newest]

Thread overview: 61+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-15  8:00 [lkp-robot] [x86/asm] 51bad67ffb: int3:#[##] kernel test robot
2018-05-15  8:00 ` kernel test robot
2018-05-15 21:07 ` Alexey Dobriyan
2018-05-15 21:07   ` Alexey Dobriyan
2018-05-15 21:25   ` Anvin, H Peter
2018-05-15 21:43     ` Alexey Dobriyan
2018-05-15 21:43       ` Alexey Dobriyan
2018-05-15 22:22       ` Josh Poimboeuf
2018-05-15 22:22         ` Josh Poimboeuf
2018-05-15 22:26         ` Thomas Gleixner
2018-05-15 22:26           ` Thomas Gleixner
2018-05-15 22:28         ` Linus Torvalds
2018-05-15 22:28           ` Linus Torvalds
2018-05-15 22:43           ` Josh Poimboeuf
2018-05-15 22:43             ` Josh Poimboeuf
2018-05-15 22:52             ` Linus Torvalds
2018-05-15 22:52               ` Linus Torvalds
2018-05-15 23:05               ` Linus Torvalds
2018-05-15 23:05                 ` Linus Torvalds
2018-05-16  3:30                 ` Josh Poimboeuf
2018-05-16  3:30                   ` Josh Poimboeuf
2018-05-17 13:49                   ` [PATCH] objtool: Detect assembly code falling through to INT3 padding Josh Poimboeuf
2018-05-17 13:49                     ` Josh Poimboeuf
2018-05-17 14:01                     ` Peter Zijlstra
2018-05-17 14:01                       ` Peter Zijlstra
2018-05-18  7:24                       ` Ingo Molnar
2018-05-18  7:24                         ` Ingo Molnar
2018-05-18  7:18                     ` Ingo Molnar
2018-05-18  7:18                       ` Ingo Molnar
2018-05-18  7:27                       ` H. Peter Anvin
2018-05-18 16:06                         ` Borislav Petkov
2018-05-18 16:06                           ` Borislav Petkov
2018-05-18  7:27                       ` Ingo Molnar
2018-05-18  7:27                         ` Ingo Molnar
2018-05-18 17:51                       ` Alexey Dobriyan
2018-05-18 17:51                         ` Alexey Dobriyan
2018-05-19  8:18                         ` hpa
2018-05-19  7:00                 ` "interesting" entry in hibernation code was Re: [lkp-robot] [x86/asm] 51bad67ffb: int3:#[##] Pavel Machek
2018-05-19  7:00                   ` Pavel Machek
2018-05-19  8:35                   ` Rafael J. Wysocki
2018-05-19  8:35                     ` Rafael J. Wysocki
2018-05-18  7:15               ` Ingo Molnar
2018-05-18  7:15                 ` Ingo Molnar
2018-05-15 22:25       ` Thomas Gleixner [this message]
2018-05-15 22:25         ` Thomas Gleixner
2018-05-15 22:29         ` Andy Lutomirski
2018-05-15 22:29           ` Andy Lutomirski
2018-05-15 22:27       ` Linus Torvalds
2018-05-15 22:27         ` Linus Torvalds
2018-05-15 22:50         ` Alexey Dobriyan
2018-05-15 22:50           ` Alexey Dobriyan
2018-05-15 22:58           ` [PATCH v2] x86/asm: Pad assembly functions with INT3 instructions Alexey Dobriyan
2018-05-15 22:58             ` Alexey Dobriyan
2018-05-15 23:28             ` Linus Torvalds
2018-05-15 23:28               ` Linus Torvalds
2018-05-18  7:36             ` Ingo Molnar
2018-05-18  7:36               ` Ingo Molnar
2018-05-18 13:02               ` Josh Poimboeuf
2018-05-18 13:02                 ` Josh Poimboeuf
2018-05-18 17:34                 ` Alexey Dobriyan
2018-05-18 17:34                   ` Alexey Dobriyan

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