linux-kernel - Re: [PATCH v8 01/15] x86/boot: Place kernel

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Message-ID: <Zc3tykqH2SjSVtd1@tomti.i.net-space.pl>
Date: Thu, 15 Feb 2024 11:56:10 +0100
From: Daniel Kiper <daniel.kiper@...cle.com>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Ross Philipson <ross.philipson@...cle.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-integrity@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-crypto@...r.kernel.org,
        kexec@...ts.infradead.org, linux-efi@...r.kernel.org,
        dpsmith@...rtussolutions.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com, dave.hansen@...ux.intel.com,
        mjg59@...f.ucam.org, James.Bottomley@...senpartnership.com,
        peterhuewe@....de, jarkko@...nel.org, jgg@...pe.ca,
        luto@...capital.net, nivedita@...m.mit.edu,
        herbert@...dor.apana.org.au, davem@...emloft.net,
        kanth.ghatraju@...cle.com, trenchboot-devel@...glegroups.com
Subject: Re: [PATCH v8 01/15] x86/boot: Place kernel_info at a fixed offset

On Thu, Feb 15, 2024 at 08:56:25AM +0100, Ard Biesheuvel wrote:
> On Wed, 14 Feb 2024 at 23:31, Ross Philipson <ross.philipson@...cle.com> wrote:
> >
> > From: Arvind Sankar <nivedita@...m.mit.edu>
> >
> > There are use cases for storing the offset of a symbol in kernel_info.
> > For example, the trenchboot series [0] needs to store the offset of the
> > Measured Launch Environment header in kernel_info.
> >
>
> Why? Is this information consumed by the bootloader?

The bootloader stuffs this info, plus some offset IIRC, into special structure
and finally it is consumed by SINIT ACM after GETSEC[SENTER] call.

Sadly this data is Intel specific and it is even not compatible with AMD.
So, if I am not mistaken, we will need additional member for the AMD in
the kernel_info.

> I'd like to get away from x86 specific hacks for boot code and boot
> images, so I would like to explore if we can avoid kernel_info, or at
> least expose it in a generic way. We might just add a 32-bit offset
> somewhere in the first 64 bytes of the bootable image: this could
> co-exist with EFI bootable images, and can be implemented on arm64,
> RISC-V and LoongArch as well.

The other architectures may or may not have need for such data due to
differences in DRTM implementation. Anyway, whatever we do I want to
be sure the DRTM can be used on UEFI and non-UEFI platforms. So, I am
not entirely convinced the address/pointer to additional DRTM data
should be part of the MS-DOS and/or PE header. Though I am not against
building something generic shared among various architectures either.

Daniel