linux-kernel - Re: [RFCv2 0/9] UEFI emulator for kexec

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Message-ID: <CAF+s44TCvG3knnqyRbw=reaCRfh0_J76HO=ykF+J=ZFyoYZOCA@mail.gmail.com>
Date: Thu, 22 Aug 2024 18:51:02 +0800
From: Pingfan Liu <piliu@...hat.com>
To: Dave Young <dyoung@...hat.com>
Cc: Lennart Poettering <mzxreary@...inter.de>, Ard Biesheuvel <ardb@...nel.org>, 
	Jan Hendrik Farr <kernel@...rr.cc>, Philipp Rudo <prudo@...hat.com>, Jarkko Sakkinen <jarkko@...nel.org>, 
	Eric Biederman <ebiederm@...ssion.com>, Baoquan He <bhe@...hat.com>, 
	Mark Rutland <mark.rutland@....com>, Will Deacon <will@...nel.org>, 
	Catalin Marinas <catalin.marinas@....com>, kexec@...ts.infradead.org, 
	linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFCv2 0/9] UEFI emulator for kexec

On Thu, Aug 22, 2024 at 2:17 PM Dave Young <dyoung@...hat.com> wrote:
>
> On Thu, 22 Aug 2024 at 13:42, Pingfan Liu <piliu@...hat.com> wrote:
> >
> > On Wed, Aug 21, 2024 at 10:27 PM Lennart Poettering
> > <mzxreary@...inter.de> wrote:
> > >
> > > On Mo, 19.08.24 22:53, Pingfan Liu (piliu@...hat.com) wrote:
> > >
> > > > *** Background ***
> > > >
> > > > As more PE format kernel images are introduced, it post challenge to kexec to
> > > > cope with the new format.
> > > >
> > > > In my attempt to add support for arm64 zboot image in the kernel [1],
> > > > Ard suggested using an emulator to tackle this issue.  Last year, when
> > > > Jan tried to introduce UKI support in the kernel [2], Ard mentioned the
> > > > emulator approach again [3]
> > >
> > > Hmm, systemd's systemd-stub code tries to load certain "side-car"
> > > files placed next to the UKI, via the UEFI file system APIs. What's
> > > your intention with the UEFI emulator regarding that? The sidecars are
> > > somewhat important, because that's how we parameterize otherwise
> > > strictly sealed, immutable UKIs.
> > >
> > IIUC, you are referring to UKI addons.
> >
> > > Hence, what's the story there? implement some form of fs driver (for
> > > what fs precisely?) in the emulator too?
> > >
> > As for addon, that is a missing part in this series. I have overlooked
> > this issue. Originally, I thought that there was no need to implement
> > a disk driver and vfat file system, just preload them into memory, and
> > finally present them through the uefi API. I will take a closer look
> > at it and chew on it.
> >
>
> Hi Pingfan,
>
> If more and more stuff needs coming in,  not only the limited boot
> services then it will be way too complicated and hard to maintain and
> debug,  also the two kexec code paths are duplicated somehow. It is
> really bad..
>
OK, I will try to keep things easier. And what do you mean about " two
kexec code paths"?

> I forgot why we can not just extract the kernel from UKI and then load
> it directly,  if the embedded kernel is also signed it should be good?
>

I think the main concern is about the signature.

Thanks,

Pingfan