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

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Message-ID: <CAF+s44S2Ph1_nFcZYy3j0Jr4yuHayb5zdNu1YXg8ce_Lf3TOgQ@mail.gmail.com>
Date: Thu, 22 Aug 2024 13:42:14 +0800
From: Pingfan Liu <piliu@...hat.com>
To: Lennart Poettering <mzxreary@...inter.de>
Cc: 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>, 
	Dave Young <dyoung@...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 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.

> And regarding tpm? tpms require drivers and i guess at the moment uefi
> emulator would run those aren't available anymore? but we really
> should do a separator measurement then. (also there needs to be some
> way to pass over measurement log of that measurement?)
>

It is a pity that it is a common issue persistent with kexec-reboot
kernel nowadays.
I am not familiar with TPM and have no clear idea for the time being.
(emulating Platform Configuration Registers ?).  But since this
emulator is held inside a linux kernel image, and the UKI's signature
is checked during kexec_file_load. All of them are safe from
modification, this security is not an urgent issue.

Thanks for sharing your thoughts and insights.

Best Regards,

Pingfan

> Lennart
>
> --
> Lennart Poettering, Berlin
>