linux-kernel - Re: [PATCH 0/3] Resolve problems with kexec identity mapping

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Message-ID: <20240708190724.GIZow47G0J8vO6J3ee@fat_crate.local>
Date: Mon, 8 Jul 2024 21:07:24 +0200
From: Borislav Petkov <bp@...en8.de>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Steve Wahl <steve.wahl@....com>, Ashish Kalra <ashish.kalra@....com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Pavin Joseph <me@...injoseph.com>,
	Eric Hagberg <ehagberg@...il.com>,
	Simon Horman <horms@...ge.net.au>,
	Eric Biederman <ebiederm@...ssion.com>,
	Dave Young <dyoung@...hat.com>, Sarah Brofeldt <srhb@....dk>,
	Russ Anderson <rja@....com>, Dimitri Sivanich <sivanich@....com>,
	Hou Wenlong <houwenlong.hwl@...group.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>, Yuntao Wang <ytcoode@...il.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Joerg Roedel <jroedel@...e.de>,
	Michael Roth <michael.roth@....com>
Subject: Re: [PATCH 0/3] Resolve problems with kexec identity mapping

On Mon, Jul 08, 2024 at 08:17:43PM +0200, Ard Biesheuvel wrote:
> Happy to assist, but I'm not sure I follow the approach here.
> 
> In the context of a confidential VM, I don't think the page fault
> handler is ever an acceptable approach. kexec should filter out config
> tables that it doesn't recognize, and map the ones that it does (note
> that EFI config tables have no standardized header with a length, so
> mapping tables it does *not* recognize is not feasible to begin with).
> 
> All these games with on-demand paging may have made sense for 64-bit
> kernels booting in 32-bit mode (which can only map the first 4G of
> RAM), but in a confiidential VM context with measurement/attestation
> etc I think the cure is worse than the disease.

See upthread. I think this is about AMD server machines which support SEV
baremetal and not about SEV-ES/SNP guests which must do attestation.

Steve?

AFAIR, there was some kink that we have to parse the blob regardless which
I didn't like either but I'd need to refresh with Tom and see whether we can
solve it differently after all. Perhaps check X86_FEATURE_HYPERVISOR or so...

Thx for offering to help still - appreciated! :-)

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette