Re: [PATCH v3] tpm/tpm_crb: Avoid unaligned reads in crb_recv()

From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: "Winkler, Tomas" <tomas.winkler@intel.com>
Cc: "linux-integrity@vger.kernel.org"
	<linux-integrity@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-security-module@vger.kernel.org" 
	<linux-security-module@vger.kernel.org>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>,
	James Morris <jmorris@namei.org>,
	Jerry Snitselaar <jsnitsel@redhat.com>
Subject: Re: [PATCH v3] tpm/tpm_crb: Avoid unaligned reads in crb_recv()
Date: Tue, 5 Feb 2019 16:35:41 +0200	[thread overview]
Message-ID: <20190205143541.GA18330@linux.intel.com> (raw)
In-Reply-To: <5B8DA87D05A7694D9FA63FD143655C1B9DA90A8B@hasmsx108.ger.corp.intel.com>

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@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>
> > ---
> > 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.

/Jarkko