linux-kernel - Re: [PATCH v3 1/2] x86_64,signal: Fix SS handling for signals delivered to 64-bit programs

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Date:	Wed, 18 Mar 2015 21:13:06 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrey Wagin <avagin@...il.com>, Andy Lutomirski <luto@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andi Kleen <andi@...stfloor.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Al Viro <viro@...iv.linux.org.uk>, X86 ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...capital.net>,
	Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [PATCH v3 1/2] x86_64,signal: Fix SS handling for signals
 delivered to 64-bit programs

On Wed, Mar 18, 2015 at 06:48:43PM +0100, Oleg Nesterov wrote:
> On 03/18, Andrey Wagin wrote:
> >
> > This commit breaks CRIU. I don't have any details yet. I'm going to
> > investigate this issue and provide more details tomorrow.
> >
> > [root@...gin-fc19-cr criu]# setsid sleep 1000 &
> > [1] 1225
> > [root@...gin-fc19-cr criu]# ps -C sleep
> >   PID TTY          TIME CMD
> >  1226 ?        00:00:00 sleep
> > [root@...gin-fc19-cr criu]# ./criu dump -t 1226 -D dump --shell-job
> > [root@...gin-fc19-cr criu]# ./criu restore -D dump --shell-job
> > Error (parasite-syscall.c:923): Task is in unexpected state: b7f (SIGSEGV)
> 
> This is funny. Because currenty I am looking into criu sources for quite
> different reason (and I HATE this reason ;)
> 
> Shot in a dark afer a quick grep: restore_gpregs() should initialize ->ss?

It hasn't been needed earlier, if this would help it means abi is broken, no? :)
Otherwise I don't understand what's happening.

> perhaps something like below... obviously uncompiled/untested.
> 
> And my grep can't find the definition of UserX86RegsEntry in crtools...
> Perhaps the change below needs CPREG1(ss, anothername).
> 
> Seriously, where is UserX86RegsEntry?

It's in protobif/core-x86.proto, welcome to protobuf hell.

> 
> Oleg.
> 
> 
> --- a/arch/x86/crtools.c
> +++ b/arch/x86/crtools.c
> @@ -475,6 +475,7 @@ int restore_gpregs(struct rt_sigframe *f, UserX86RegsEntry *r)
>  	CPREG2(rip, ip);
>  	CPREG2(eflags, flags);
>  	CPREG1(cs);
> +	CPREG1(ss);
>  	CPREG1(gs);
>  	CPREG1(fs);
>  
> diff --git a/arch/x86/include/asm/restorer.h b/arch/x86/include/asm/restorer.h
> index 70199fb..c04fb94 100644
> --- a/arch/x86/include/asm/restorer.h
> +++ b/arch/x86/include/asm/restorer.h
> @@ -53,7 +53,7 @@ struct rt_sigcontext {
>  	unsigned short			cs;
>  	unsigned short			gs;
>  	unsigned short			fs;
> -	unsigned short			__pad0;
> +	unsigned short			ss;
>  	unsigned long			err;
>  	unsigned long			trapno;
>  	unsigned long			oldmask;
> 

	Cyrill
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