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

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Message-ID: <20150915164619.GA7164@intel.com>
Date:	Tue, 15 Sep 2015 19:46:19 +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] tpm, tpm_crb: fix unaligned read of the command buffer
 address

On Tue, Sep 15, 2015 at 10:30:39AM -0600, Jason Gunthorpe wrote:
> On Tue, Sep 15, 2015 at 01:09:56PM +0300, Jarkko Sakkinen wrote:
> > However, for MMIO address the hardware might abort the entire request
> > when trying to do a 64-bit read, which causes the CPU to fill the result
> > with 1's.
> 
> Okay, yes, for iomem you can't rely on packed.
> 
> packed actually can mess up iomem loads on some arches as it also
> tells the compiler things are unaligned. I'd drop the __packed since
> the new structure is naturally packed in this case. (for other cases
> be careful to add __aligned(2) to avoid unaligned accesses)
> 
> However, I'm still confused, the original code did:
>  	memcpy_fromio(&pa, &priv->cca->cmd_pa, 8);
> 
> Which might do byte reads from the iomem cmd_pa, but there should be
> no problem with an unaligned access.
> 
> Is the real issue that you can't do memcpy_fromio to tpm control
> memory? That would not suprise me one bit. In which case the commit
> message should be revised.

Good question and point. Emprically it seems to be so. I guess you
have to do exactly 32-bit read for the field. I'll revise the commit
message.

> > This is not hypothetical bug. We are experiencing this on some platforms
> > and the proposed fix resolves the issue.
> 
> I am confused because of the memcpy_fromio:
> 
>  	memcpy_fromio(&pa, &priv->cca->cmd_pa, 8);
> -	pa = le64_to_cpu(pa);
> +
> +	pa = ((u64) le32_to_cpu(ioread32(&priv->cca->cmd_pa_high)) << 32) +
> +		(u64) le32_to_cpu(ioread32(&priv->cca->cmd_pa_low));
>  	priv->cmd = devm_ioremap_nocache(dev, pa,
>  					 ioread32(&priv->cca->cmd_size));
> 
> The code wasn't doing a direct load from cmd_pa, so the type doesn't
> matter.
> 
> BTW. Does the above even compile with that memcpy_fromio left in?

Nope :) See my own reply to the original message.

> Jason

/Jarkko
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