linux-kernel - Re: [PATCH v2 1/2] efi+tpm: Don't access event->count when it isn't mapped.

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Message-ID: <20190927152938.GB10545@linux.intel.com>
Date:   Fri, 27 Sep 2019 18:29:38 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        Peter Jones <pjones@...hat.com>,
        linux-efi <linux-efi@...r.kernel.org>,
        stable <stable@...r.kernel.org>, Lyude Paul <lyude@...hat.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        Bartosz Szczepanek <bsz@...ihalf.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] efi+tpm: Don't access event->count when it isn't
 mapped.

On Wed, Sep 25, 2019 at 09:41:33AM -0700, Jerry Snitselaar wrote:
> On Wed Sep 25 19, Jerry Snitselaar wrote:
> > On Wed Sep 25 19, Jarkko Sakkinen wrote:
> > > On Wed, Sep 25, 2019 at 12:25:05PM +0200, Ard Biesheuvel wrote:
> > > > On Wed, 25 Sep 2019 at 12:16, Jarkko Sakkinen
> > > > <jarkko.sakkinen@...ux.intel.com> wrote:
> > > > > 
> > > > > From: Peter Jones <pjones@...hat.com>
> > > > > 
> > > > > Some machines generate a lot of event log entries.  When we're
> > > > > iterating over them, the code removes the old mapping and adds a
> > > > > new one, so once we cross the page boundary we're unmapping the page
> > > > > with the count on it.  Hilarity ensues.
> > > > > 
> > > > > This patch keeps the info from the header in local variables so we don't
> > > > > need to access that page again or keep track of if it's mapped.
> > > > > 
> > > > > Fixes: 44038bc514a2 ("tpm: Abstract crypto agile event size calculations")
> > > > > Cc: linux-efi@...r.kernel.org
> > > > > Cc: linux-integrity@...r.kernel.org
> > > > > Cc: stable@...r.kernel.org
> > > > > Signed-off-by: Peter Jones <pjones@...hat.com>
> > > > > Tested-by: Lyude Paul <lyude@...hat.com>
> > > > > Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > > > > Acked-by: Matthew Garrett <mjg59@...gle.com>
> > > > > Acked-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> > > > > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > > > 
> > > > Thanks Jarkko.
> > > > 
> > > > Shall I take these through the EFI tree?
> > > 
> > > Would be great, if you could because I already sent one PR with fixes for
> > > v5.4-rc1 yesterday.
> > > 
> > > /Jarkko
> > 
> > My patch collides with this, so I will submit a v3 that applies on top of
> > these once I've run a test with all 3 applied on this t480s.
> 
> Tested with Peter's patches, and that was the root cause on this 480s.
> 
> I think there should still be a check for tbl_size to make sure we
> aren't sticking -1 into efi_tpm_final_log_size though, which will be
> the case right now if it fails to parse an event.

You could sent a follow up patch for that I think. The current
ones are kind of already "went through the process" and do right
things but I do agree that a sanity check would make sense just
in case.

/Jarkko