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

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Date:   Fri, 7 Jul 2023 19:12:17 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Michael Roth <michael.roth@....com>
Cc:     Joerg Roedel <jroedel@...e.de>, Baoquan He <bhe@...hat.com>,
        Tao Liu <ltao@...hat.com>, thomas.lendacky@....com,
        tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, ardb@...nel.org,
        linux-kernel@...r.kernel.org, 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 Fri, Jul 07, 2023 at 10:25:15AM -0500, Michael Roth wrote:
> ...
> It would be unfortunate if we finally abandoned this path because of the
> issue being hit here though. I think the patch posted here is the proper
> resolution to the issue being hit, and I'm hoping at this point we've
> identified all the similar cases where EFI/setup_data-related structures
> were missing explicit mappings. But if we still think it's too much of a
> liability to access the EFI config table outside of SEV-enabled guests,
> then I can work on re-implementing things based on the above logic.

Replying here to Tom's note too...

So, I like the idea of rechecking CPUID. Yes, let's do the sev_status
check. As a result, we either fail the guest - no problem - or we boot
and we recheck. Thus, we don't run AMD code on !AMD machines, if the HV
is not a lying bastard.

Now, if we've gotten a valid setup_data SETUP_EFI entry with a valid
pointer to an EFI config table, then that should happen in the generic
path - initialize_identity_maps(), for example - like you've done in
b57feed2cc26 - not in the kexec code because kexec *happens* to need it.

We want to access the EFI config table? Sure, by all means, but make
that generic for all code.

Thx.

-- 
Regards/Gruss,
    Boris.

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