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

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Date:   Fri, 25 Sep 2020 09:00:56 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     linux-integrity <linux-integrity@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>
Subject: Re: [PATCH] tpm: of: avoid __va() translation for event log address

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?


> > So instead, use memremap(), which will reuse the linear mapping if
> > it is valid, or create another mapping otherwise.
> >
> > Cc: Peter Huewe <peterhuewe@....de>
> > Cc: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > Cc: Jason Gunthorpe <jgg@...pe.ca>
> > Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> > ---
> >  drivers/char/tpm/eventlog/of.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/char/tpm/eventlog/of.c b/drivers/char/tpm/eventlog/of.c
> > index a9ce66d09a75..9178547589a3 100644
> > --- a/drivers/char/tpm/eventlog/of.c
> > +++ b/drivers/char/tpm/eventlog/of.c
> > @@ -11,6 +11,7 @@
> >   */
> >
> >  #include <linux/slab.h>
> > +#include <linux/io.h>
> >  #include <linux/of.h>
> >  #include <linux/tpm_eventlog.h>
> >
> > @@ -25,6 +26,7 @@ int tpm_read_log_of(struct tpm_chip *chip)
> >       struct tpm_bios_log *log;
> >       u32 size;
> >       u64 base;
> > +     void *p;
>
> I'd just use 'ptr' for readability sake.
>

If you prefer

> >       log = &chip->log;
> >       if (chip->dev.parent && chip->dev.parent->of_node)
> > @@ -65,7 +67,11 @@ int tpm_read_log_of(struct tpm_chip *chip)
> >               return -EIO;
> >       }
> >
> > -     log->bios_event_log = kmemdup(__va(base), size, GFP_KERNEL);
> > +     p = memremap(base, size, MEMREMAP_WB);
> > +     if (!p)
> > +             return -ENOMEM;
> > +     log->bios_event_log = kmemdup(p, size, GFP_KERNEL);
> > +     memunmap(p);
> >       if (!log->bios_event_log)
> >               return -ENOMEM;
> >
> > --
> > 2.17.1
> >
>
> This is a really great catch!
>
> I'm a bit late of my PR a bit because of SGX upstreaming madness
> (sending v39 soon). If you can answer to my question above, I can do
> that nitpick change to patch and get it to my v5.10 PR.
>

Yes, please.

> PS. Just so that you know, once I've applied it, it will be available
> here:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd.git
>
> I'll include MAINTAINERS update to that PR.
>
> /Jarkko