linux-kernel - Re: [RFC] efi/tpm: add efi.tpm_log as a reserved region in 820_table

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Message-ID: <5c525fe8f33fffebc0d275086cc7484e309dfae0.camel@HansenPartnership.com>
Date: Fri, 13 Sep 2024 08:07:18 -0400
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: Breno Leitao <leitao@...ian.org>
Cc: Ard Biesheuvel <ardb@...nel.org>, Usama Arif <usamaarif642@...il.com>, 
 linux-efi@...r.kernel.org, kexec@...ts.infradead.org,
 ebiederm@...ssion.com,  bhe@...hat.com, vgoyal@...hat.com,
 tglx@...utronix.de, dave.hansen@...ux.intel.com,  x86@...nel.org,
 linux-kernel@...r.kernel.org, rmikey@...a.com, gourry@...rry.net
Subject: Re: [RFC] efi/tpm: add efi.tpm_log as a reserved region in
 820_table_firmware

On Fri, 2024-09-13 at 04:57 -0700, Breno Leitao wrote:
> Hello James,
> 
> On Thu, Sep 12, 2024 at 12:22:01PM -0400, James Bottomley wrote:
> > On Thu, 2024-09-12 at 06:03 -0700, Breno Leitao wrote:
> > > Hello Ard,
> > > 
> > > On Thu, Sep 12, 2024 at 12:51:57PM +0200, Ard Biesheuvel wrote:
> > > > I don't see how this could be an EFI bug, given that it does
> > > > not deal with E820 tables at all.
> > > 
> > > I want to back up a little bit and make sure I am following the
> > > discussion.
> > > 
> > > From what I understand from previous discussion, we have an EFI
> > > bug as the root cause of this issue.
> > > 
> > > This happens because the EFI does NOT mark the EFI TPM event log
> > > memory region as reserved (EFI_RESERVED_TYPE). Not having an
> > > entry for the event table memory in EFI memory mapped, then
> > > libstub will ignore it completely (the TPM event log memory
> > > range) and not populate e820 table with it.
> > 
> > Wait, that's not correct.  The TPM log is in memory that doesn't
> > survive ExitBootServices (by design in case the OS doesn't care
> > about it).  So the EFI stub actually copies it over to a new
> > configuration table that is in reserved memory before it calls
> > ExitBootServices.  This new copy should be in kernel reserved
> > memory regardless of its e820 map status.
> 
> First of all, thanks for clarifying some points here.
> 
> How should the TPM log table be passed to the next kernel when
> kexecing() since it didn't surive ExitBootServices?

I've no idea.  I'm assuming you don't elaborately reconstruct the EFI
boot services, so you can't enter the EFI boot stub before
ExitBootServices is called?  So I'd guess you want to preserve the EFI
table that copied the TPM data in to kernel memory.

James