Re: [PATCH] tpm/tpm_crb: Avoid unaligned reads in crb_recv()

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Mon, Apr 15, 2019 at 12:48:25PM +0200, Greg KH wrote:
> On Wed, Apr 10, 2019 at 04:54:32PM +0300, Jarkko Sakkinen wrote:
> > commit 3d7a850fdc1a2e4d2adbc95cc0fc962974725e88 upstream
> > 
> > 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@vger.kernel.org
> > Cc: James Morris <jmorris@namei.org>
> > Cc: Tomas Winkler <tomas.winkler@intel.com>
> > Cc: Jerry Snitselaar <jsnitsel@redhat.com>
> > Fixes: 30fc8d138e91 ("tpm: TPM 2.0 CRB Interface")
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> > Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
> > Acked-by: Tomas Winkler <tomas.winkler@intel.com>
> > ---
> > backport v4.4.178
> >  drivers/char/tpm/tpm_crb.c | 22 ++++++++++++++++------
> >  1 file changed, 16 insertions(+), 6 deletions(-)
> 
> I need a 4.9.y version first before I can take a 4.4.y version, as we do
> not want anyone to have a regression moving from 4.4.y to a newer
> kernel.

OK, will do.

/Jarkko