linux-kernel - Re: [PATCH 0/6] kexec: A new system call to allow in kernel loading

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Message-ID: <20131121190729.GI16208@redhat.com>
Date:	Thu, 21 Nov 2013 14:07:29 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	ebiederm@...ssion.com, hpa@...or.com, mjg59@...f.ucam.org
Subject: Re: [PATCH 0/6] kexec: A new system call to allow in kernel loading

On Thu, Nov 21, 2013 at 10:58:28AM -0800, Greg KH wrote:
> On Wed, Nov 20, 2013 at 12:50:45PM -0500, Vivek Goyal wrote:
> > Current proposed secureboot implementation disables kexec/kdump because
> > it can allow unsigned kernel to run on a secureboot platform. Intial
> > idea was to sign /sbin/kexec binary and let that binary do the kernel
> > signature verification. I had posted RFC patches for this apparoach
> > here.
> > 
> > https://lkml.org/lkml/2013/9/10/560
> > 
> > Later we had discussion at Plumbers and most of the people thought
> > that signing and trusting /sbin/kexec is becoming complex. So a 
> > better idea might be let kernel do the signature verification of
> > new kernel being loaded. This calls for implementing a new system call
> > and moving lot of user space code in kernel.
> > 
> > kexec_load() system call allows loading a kexec/kdump kernel and jump
> > to that kernel at right time. Though a lot of processing is done in
> > user space which prepares a list of segments/buffers to be loaded and
> > kexec_load() works on that list of segments. It does not know what's
> > contained in those segments.
> > 
> > Now a new system call kexec_file_load() is implemented which takes
> > kernel fd and initrd fd as parameters. Now kernel should be able
> > to verify signature of newly loaded kernel. 
> > 
> > This is an early RFC patchset. I have not done signature handling
> > part yet. This is more of a minimal patch to show how new system
> > call and functionality will look like. Right now it can only handle
> > bzImage with 64bit entry point on x86_64. No EFI, no x86_32  or any
> > other architecture. Rest of the things can be added slowly as need
> > arises. In first iteration, I have tried to address most common use case
> > for us.
> 
> Very good stuff, thanks for working on this.  How have you been testing
> this on the userspace side?  Are there patches to kexec, or are you just
> using a small test program with the new syscall?

I wrote a patch for kexec-tools. One can choose to use new system call
by passing command line option --use-kexec2-syscall. I will post
that patch soon in this mail thread.

Thanks
Vivek
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