linux-kernel - Re: [PATCH v2] x86/kexec: Add EFI config table identity mapping for kexec kernel

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Message-ID: <20230802155146.GCZMp7ksDdN2ETVzKV@fat_crate.local>
Date:   Wed, 2 Aug 2023 17:51:46 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Ard Biesheuvel <ardb@...nel.org>,
        Jörg Rödel <joro@...tes.org>
Cc:     Tom Lendacky <thomas.lendacky@....com>, Tao Liu <ltao@...hat.com>,
        Michael Roth <michael.roth@....com>, tglx@...utronix.de,
        mingo@...hat.com, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, linux-kernel@...r.kernel.org, bhe@...hat.com,
        dyoung@...hat.com, kexec@...ts.infradead.org,
        linux-efi@...r.kernel.org
Subject: Re: [PATCH v2] x86/kexec: Add EFI config table identity mapping for
 kexec kernel

On Wed, Aug 02, 2023 at 04:55:27PM +0200, Ard Biesheuvel wrote:
> ... because now, entering via startup_32 is broken, given that it only
> maps the kernel image itself and relies on the #PF handling for
> everything else it accesses, including firmware tables.
> 
> AFAICT this also means that entering via startup_32 is broken entirely
> for any configuration that enables the cc blob config table check,
> regardless of the platform.

Lemme brain-dump what Tom and I just talked on IRC.

That startup_32 entry path for SNP guests was used with old grubs which
used to enter through there and not anymore, reportedly. Which means,
that must've worked at some point but Joerg would know. CCed.

Newer grubs enter through the 64-bit entry point and thus are fine
- otherwise we would be seeing explosions left and right.

So dependent on what we wanna do, if we kill the 32-bit path, we can
kill the 32-bit C-bit verif code. But that's for later and an item on my
TODO list.

Thx.

-- 
Regards/Gruss,
    Boris.

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