linux-kernel - Re: [PATCH v3] tpm, tpm_crb: fix unaligned read of the command buffer address

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Message-ID: <20150916133427.GA5991@intel.com>
Date:	Wed, 16 Sep 2015 16:34:27 +0300
From:	Jarkko Sakkinen <jarkko.sakkinen@...el.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
	tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	Peter Huewe <peterhuewe@....de>,
	Marcel Selhorst <tpmdd@...horst.net>
Subject: Re: [PATCH v3] tpm, tpm_crb: fix unaligned read of the command
 buffer address

On Wed, Sep 16, 2015 at 10:19:17AM +0300, Jarkko Sakkinen wrote:
> On Tue, Sep 15, 2015 at 11:22:27AM -0600, Jason Gunthorpe wrote:
> > On Tue, Sep 15, 2015 at 08:05:40PM +0300, Jarkko Sakkinen wrote:
> > > The command buffer address must be read with exactly two 32-bit reads.
> > > Otherwise, on some HW platforms, it seems that HW will abort the read
> > > operation, which causes CPU to fill the read bytes with 1's. Therefore,
> > > we cannot rely on memcpy_fromio() but must call ioread32() two times
> > > instead.
> > > 
> > > Also, this matches the PC Client Platform TPM Profile specification,
> > > which defines command buffer address with two 32-bit fields.
> > > 
> > > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > >  drivers/char/tpm/tpm_crb.c | 7 ++++---
> > >  1 file changed, 4 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c
> > > index b4564b6..c09b370 100644
> > > +++ b/drivers/char/tpm/tpm_crb.c
> > > @@ -68,7 +68,8 @@ struct crb_control_area {
> > >  	u32 int_enable;
> > >  	u32 int_sts;
> > >  	u32 cmd_size;
> > > -	u64 cmd_pa;
> > > +	u32 cmd_pa_low;
> > > +	u32 cmd_pa_high;
> > >  	u32 rsp_size;
> > >  	u64 rsp_pa;
> > 
> > What about rsp_pa?
> 
> It's naturally aligned and defined as 64-bit field in:
> 
> http://www.trustedcomputinggroup.org/developers/pc_client/specifications
> 
> Also in a platform (not available in public yet) it gets read correctly.

memcpy_64.S uses rep movsq and rep movsb for the remainder. That's why
the read failed in the case of cmd address but it does not fail with rsp
address.

See http://lxr.free-electrons.com/source/arch/x86/lib/memcpy_64.S

> > >  } __packed;
> > 
> > As I mentioned, drop the __packed.
> 
> I didn't do that because it is not mandatory for the bug fix.
> 
> I would rather submit it as a separate commit later on.
> 
> > Otherwise:
> > 
> > Reviewed-By: Jason Gunthorpe <jgunthorpe@...idianresearch.com>
> > 
> > Jason
> 
> /Jarkko

/Jarkko
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