Re: [PATCH v3] tpm/tpm_crb: Avoid unaligned reads in crb_recv()
From: Jarkko Sakkinen
Date: Tue Feb 05 2019 - 15:57:28 EST
On Tue, Feb 05, 2019 at 02:56:02PM +0000, Winkler, Tomas wrote:
> > -----Original Message-----
> > From: Jarkko Sakkinen [mailto:jarkko.sakkinen@xxxxxxxxxxxxxxx]
> > Sent: Tuesday, February 05, 2019 16:36
> > To: Winkler, Tomas <tomas.winkler@xxxxxxxxx>
> > Cc: linux-integrity@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-
> > security-module@xxxxxxxxxxxxxxx; stable@xxxxxxxxxxxxxxx; James Morris
> > <jmorris@xxxxxxxxx>; Jerry Snitselaar <jsnitsel@xxxxxxxxxx>
> > Subject: Re: [PATCH v3] tpm/tpm_crb: Avoid unaligned reads in crb_recv()
> > On Tue, Feb 05, 2019 at 11:07:16AM +0000, Winkler, Tomas wrote:
> > > > The current approach to read first 6 bytes from the response and
> > > > then tail of the response, can cause the 2nd memcpy_fromio() to do
> > > > an unaligned read (e.g. read 32-bit word from address aligned to a
> > > > 16-bits), depending on how
> > > > memcpy_fromio() is implemented. If this happens, the read will fail
> > > > and the memory controller will fill the read with 1's.
> > > >
> > > > This was triggered by 170d13ca3a2f, which should be probably refined
> > > > to check and react to the address alignment. Before that commit, on
> > > > x86
> > > > memcpy_fromio() turned out to be memcpy(). By a luck GCC has done
> > > > the right thing (from tpm_crb's perspective) for us so far, but we should not
> > rely on that.
> > > > Thus, it makes sense to fix this also in tpm_crb, not least because
> > > > the fix can be then backported to stable kernels and make them more
> > > > robust when compiled in differing environments.
> > > >
> > > > Cc: stable@xxxxxxxxxxxxxxx
> > > > Cc: James Morris <jmorris@xxxxxxxxx>
> > > > Cc: Tomas Winkler <tomas.winkler@xxxxxxxxx>
> > > > Cc: Jerry Snitselaar <jsnitsel@xxxxxxxxxx>
> > > > Fixes: 30fc8d138e91 ("tpm: TPM 2.0 CRB Interface")
> > > > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
> > > > Reviewed-by: Jerry Snitselaar <jsnitsel@xxxxxxxxxx>
> > > > ---
> > > > v3:
> > > > * Fix typo i.e. %s/reminding/remaining/g
> > >
> > > Why you haven't fixed all the typos I've pointed out? I think you missed that.
> > I saw only comment about remaining. Was there something else? Can fix.
> 1. unrecovable -> unrecoverable
> 2. /* Read 8 bytes (not just 6 bytes, which would cover the tag and the response length
> > + * fields) in order to make sure that the remaining memory accesses */
Thanks and apologies for missing these.