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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 1 Feb 2019 10:04:35 -0800
Message-ID: <CAHk-=whO_TqDzQXSuSbgyZdVj9qeyRSxpjWXBQUWgvKGT2dnug@mail.gmail.com>
Subject: Re: Getting weird TPM error after rebasing my tree to security/next-general
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc:     Tomas Winkler <tomas.winkler@intel.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        James Bottomley <James.Bottomley@hansenpartnership.com>,
        linux-integrity@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>
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On Thu, Jan 31, 2019 at 12:45 PM Jarkko Sakkinen
<jarkko.sakkinen@linux.intel.com> wrote:
>
> I understand what you mean. Just surprised that this hasn't failed
> before to anyone (the same driver has been even successfully used
> on ARM64 with TrustZone based fTPM implementation). It has been in
> for three years now.

Just to finish this thread off: it turns out that both ARM and ARM64
worked fine, because neither did a memcpy(), but had explicit IO copy
routines.

And in those explicit routines, 32-bit ARM did only byte accesses, and
64-bit ARM did 8-byte accesses for the bulk transfer part, but byte
accesses for the unaligned head and tail of the IO area.

So I think it's all good. x86 used to work by luck (either because all
machines that used that TPM chip always had ERMS, or because the
people who didn't have it never cared), and ARM just worked because it
would never do unaligned IO accesses anyway (well, I guess you can
force them with "readl()" on an unaligned address, but then you just
have yourself to blame).

           Linus