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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALCETrVuF3uL77UZNVvXTQrLpycDNmm-FiH-gXSPsWa-fb1koQ@mail.gmail.com>
Date:	Wed, 18 Mar 2015 11:32:25 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Cyrill Gorcunov <gorcunov@...il.com>,
	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>,
	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 11:25 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 03/18, Cyrill Gorcunov wrote:
>>
>> On Wed, Mar 18, 2015 at 11:06:00AM -0700, Andy Lutomirski wrote:
>> > > --- 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);
>> >
>> > Huh?  Is CRIU actually trying to build an entire sigcontext from
>> > scratch here?  I don't see how this can reliably work across kernel
>> > versions or CPU versions.
>>
>> Yes we are. And why it can't work reliably? As to CPU -- we're
>> testing that cpu features saved in image should match ones
>> provided by the kernel runtime, ie on the machine where we're
>> restoring.
>
> But, say, __USER_CS can be changed in kernel, and nobody should notice this.

This actually happens on a regular basis.  Has anyone tried
checkpointing on Xen and restoring on native?  Xen does interesting
things to cs and possibly to ss as well on x86.

You get somewhat of a free pass on ds and es because the kernel's
context switch code is very tolerant of failures there.

--Andy
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/