linux-kernel - Re: [PATCH 14/14] arm64: kexec_file: add vmlinux format support

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Message-ID: <20170908030750.GF17186@linaro.org>
Date:   Fri, 8 Sep 2017 12:07:51 +0900
From:   AKASHI Takahiro <takahiro.akashi@...aro.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     herbert@...dor.apana.org.au, bhe@...hat.com,
        ard.biesheuvel@...aro.org, catalin.marinas@....com,
        will.deacon@....com, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org, dhowells@...hat.com, arnd@...db.de,
        linux-arm-kernel@...ts.infradead.org, mpe@...erman.id.au,
        bauerman@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
        dyoung@...hat.com, davem@...emloft.net, vgoyal@...hat.com
Subject: Re: [PATCH 14/14] arm64: kexec_file: add vmlinux format support

On Tue, Aug 29, 2017 at 11:01:12AM +0100, Mark Rutland wrote:
> On Thu, Aug 24, 2017 at 06:30:50PM +0100, Mark Rutland wrote:
> > On Thu, Aug 24, 2017 at 05:18:11PM +0900, AKASHI Takahiro wrote:
> > > The first PT_LOAD segment, which is assumed to be "text" code, in vmlinux
> > > will be loaded at the offset of TEXT_OFFSET from the begining of system
> > > memory. The other PT_LOAD segments are placed relative to the first one.
> > 
> > I really don't like assuming things about the vmlinux ELF file.
> > 
> > > Regarding kernel verification, since there is no standard way to contain
> > > a signature within elf binary, we follow PowerPC's (not yet upstreamed)
> > > approach, that is, appending a signature right after the kernel binary
> > > itself like module signing.
> > 
> > I also *really* don't like this. It's a bizarre in-band mechanism,
> > without explcit information. It's not a nice ABI.
> > 
> > If we can load an Image, why do we need to be able to load a vmlinux?
> 
> So IIUC, the whole point of this is to be able to kexec_file_load() a
> vmlinux + signature bundle, for !CONFIG_EFI kernels.
> 
> For that, I think that we actually need a new kexec_file_load${N}
> syscall, where we can pass the signature for the kernel as a separate
> file. Ideally also with a flags argument and perhaps the ability to sign
> the initrd too.

Verifying root file system would be another topic in general.

> That way we don't ahve to come up with a magic vmlinux+signature format,
> as we can just pass a regular image and a signature for that image
> separately. That should work for PPC and others, too.

Since some discussions are to be expected around vmlinux signing,
I will drop vmlinux support in v2.

(This means, as you mentioned, that we have no way to sign
a !CONFIG_EFI kernel for now. The possible solution in future would
be to utilize file extended attributes as proposed by powerpc guys?)

Thanks,
-Takahiro AKASHI

> Thanks,
> Mark.