Re: [PATCH v8 01/15] x86/boot: Place kernel_info at a fixed offset

From: Daniel Kiper <daniel.kiper@oracle.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Ross Philipson <ross.philipson@oracle.com>,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	linux-integrity@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-crypto@vger.kernel.org, kexec@lists.infradead.org,
	linux-efi@vger.kernel.org, dpsmith@apertussolutions.com,
	tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	hpa@zytor.com, dave.hansen@linux.intel.com, mjg59@srcf.ucam.org,
	James.Bottomley@hansenpartnership.com, peterhuewe@gmx.de,
	jarkko@kernel.org, jgg@ziepe.ca, luto@amacapital.net,
	nivedita@alum.mit.edu, herbert@gondor.apana.org.au,
	davem@davemloft.net, kanth.ghatraju@oracle.com,
	trenchboot-devel@googlegroups.com
Subject: Re: [PATCH v8 01/15] x86/boot: Place kernel_info at a fixed offset
Date: Thu, 15 Feb 2024 11:56:10 +0100	[thread overview]
Message-ID: <Zc3tykqH2SjSVtd1@tomti.i.net-space.pl> (raw)
In-Reply-To: <CAMj1kXH3Gvr3vDRLDdXuc0s7ZAQYE6+D7tmCRBjJWwWt2fn4-w@mail.gmail.com>

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@oracle.com> wrote:
> >
> > From: Arvind Sankar <nivedita@alum.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

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