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

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Message-ID: <32FDA47A-C87F-406F-A0B9-3AA1BB2EBAFB@zytor.com>
Date: Fri, 22 Mar 2024 07:18:58 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: "Daniel P. Smith" <dpsmith@...rtussolutions.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Ross Philipson <ross.philipson@...cle.com>
CC: 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, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, 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 March 21, 2024 6:45:48 AM PDT, "Daniel P. Smith" <dpsmith@...rtussolutions.com> wrote:
>Hi Ard!
>
>On 2/15/24 02:56, 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?
>
>Yes, the bootloader needs a standardized means to find the offset of the MLE header, which communicates a set of meta-data needed by the DCE in order to set up for and start the loaded kernel. Arm will also need to provide a similar metadata structure and alternative entry point (or a complete rewrite of the existing entry point), as the current Arm entry point is in direct conflict with Arm DRTM specification.
>
>> 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.
>
>With all due respect, I would not refer to boot params and the kern_info extension designed by the x86 maintainers as a hack. It is the well-defined boot protocol for x86, just as Arm has its own boot protocol around Device Tree.
>
>We would gladly adopt a cross arch/cross image type, zImage and bzImage, means to embedded meta-data about the kernel that can be discovered by a bootloader. Otherwise, we are relegated to doing a per arch/per image type discovery mechanism. If you have any suggestions that are cross arch/cross image type that we could explore, we would be grateful and willing to investigate how to adopt such a method.
>
>V/r,
>Daniel

To be fair, the way things are going UEFI, i.e. PE/COFF, is becoming the new standard format. Yes, ELF would have been better, but...