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Date:   Tue, 29 Jan 2019 15:20:16 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     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>
Subject: Re: Getting weird TPM error after rebasing my tree to
 security/next-general
Message-ID: <20190129132016.GA1602@linux.intel.com>
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On Thu, Jan 24, 2019 at 07:43:30AM +1300, Linus Torvalds wrote:
> On Thu, Jan 24, 2019 at 4:36 AM Jarkko Sakkinen
> <jarkko.sakkinen@linux.intel.com> wrote:
> > >
> > > Is it just that this particular hardware always happened to trigger
> > > the ERMS case (ie "rep movsb")?
> >
> > This is the particular snippet in question:
> >
> > memcpy_fromio(buf, priv->rsp, 6);
> > expected = be32_to_cpup((__be32 *) &buf[2]);
> > if (expected > count || expected < 6)
> >         return -EIO;
> 
> Ok, strange.
> 
> So what *used* to happen is that the memcpy_fromio() would just expand
> as a "memcpy()", and in this case, gcc would then inline the memcpy().
> In fact, gcc does it as a 4-byte access and a two-byte access from
> what I can tell.

I verified, and it is exactly as you stated:

   0xffffffff814aaa33 <+51>:	mov    (%rax),%edx
   0xffffffff814aaa35 <+53>:	mov    %edx,0x0(%rbp)
   0xffffffff814aaa38 <+56>:	movzwl 0x4(%rax),%eax
   0xffffffff814aaa3c <+60>:	mov    %ax,0x4(%rbp)

And your new version does exactly the same thing to the first six bytes
(with different opcode, but the same memory access pattern).

/Jarkko