linux-kernel - Re: [PATCH] tpm: of: avoid __va() translation for event log address

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Message-ID: <20200925120018.GH9916@ziepe.ca>
Date:   Fri, 25 Sep 2020 09:00:18 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Huewe <peterhuewe@....de>
Subject: Re: [PATCH] tpm: of: avoid __va() translation for event log address

On Fri, Sep 25, 2020 at 01:29:20PM +0300, Jarkko Sakkinen wrote:
> On Fri, Sep 25, 2020 at 09:00:56AM +0200, Ard Biesheuvel wrote:
> > On Fri, 25 Sep 2020 at 07:56, Jarkko Sakkinen
> > <jarkko.sakkinen@...ux.intel.com> wrote:
> > >
> > > On Tue, Sep 22, 2020 at 11:41:28AM +0200, Ard Biesheuvel wrote:
> > > > The TPM event log is provided to the OS by the firmware, by loading
> > > > it into an area in memory and passing the physical address via a node
> > > > in the device tree.
> > > >
> > > > Currently, we use __va() to access the memory via the kernel's linear
> > > > map: however, it is not guaranteed that the linear map covers this
> > > > particular address, as we may be running under HIGHMEM on a 32-bit
> > > > architecture, or running firmware that uses a memory type for the
> > > > event log that is omitted from the linear map (such as EfiReserved).
> > >
> > > Makes perfect sense to the level that I wonder if this should have a
> > > fixes tag and/or needs to be backported to the stable kernels?
> > >
> > 
> > AIUI, the code was written specifically for ppc64, which is a
> > non-highmem, non-EFI architecture. However, when we start reusing this
> > driver for ARM, this issue could pop up.
> > 
> > The code itself has been refactored a couple of times, so I think it
> > will require different versions of the patch for different generations
> > of stable kernels.
> > 
> > So perhaps just add Cc: <stable@...r.kernel.org>, and wait and see how
> > far back it applies cleanly?
> 
> Yeah, I think I'll cc it with some note before the diffstat.
> 
> I'm thinking to cap it to only 5.x kernels (at least first) unless it is
> dead easy to backport below that.

I have this vauge recollection of pointing at this before and being
told that it had to be __va for some PPC reason?

Do check with the PPC people first, I see none on the CC list.

Jason