linux-kernel - Re: Kdump with signed images

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Message-ID: <87k3tynvc0.fsf@xmission.com>
Date:	Tue, 06 Nov 2012 15:51:59 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Matthew Garrett <mjg@...hat.com>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Khalid Aziz <khalid@...ehiking.org>, kexec@...ts.infradead.org,
	horms@...ge.net.au, Dave Young <dyoung@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Dmitry Kasatkin <dmitry.kasatkin@...el.com>,
	Roberto Sassu <roberto.sassu@...ito.it>,
	Kees Cook <keescook@...omium.org>,
	Peter Jones <pjones@...hat.com>
Subject: Re: Kdump with signed images

Vivek Goyal <vgoyal@...hat.com> writes:

> On Mon, Nov 05, 2012 at 11:44:48AM -0800, Eric W. Biederman wrote:
>> Vivek Goyal <vgoyal@...hat.com> writes:
>> 
>> > On Fri, Nov 02, 2012 at 02:32:48PM -0700, Eric W. Biederman wrote:
>> >> 
>> >> It needs to be checked but /sbin/kexec should not use any functions that
>> >> trigger nss switch.  No user or password or host name lookup should be
>> >> happening.
>> >
>> > I also think that we don't call routines which trigger nss switch but
>> > be probably can't rely on that as somebody might introduce it in
>> > future. So we need more robust mechanism to prevent it than just code
>> > inspection.
>> 
>> The fact that we shouldn't use those routines is enough to let us
>> walk down a path where they are not used.  Either with a static glibc
>> linked told to use no nss modules (--enable-static-nss ?), or with
>> another more restricted libc.
>
> I installed glibc-static and built kexec-tools using gcc "-static" option.
> It built just fine and infact kdump is working with it.
>
> Size of new kexec binary is around 1.4MB.
>
> Did not get any warning w.r.t nss, so I am assuming we are not calling
> any relevant functions.
>
> I did try building my own libc using --enable-static-nss but it does not
> seem to have built static versions of libnss*. Will look more into it
> and try linking kexec with this new glibc and see if that works.
>
> Also tried playing with klibc and uclibc a bit but can't get anything
> going quickly.

Sounds good.  It has been about a year since I looked but kexec built
uclibc just fine last time I tried it.

Eric

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