linux-kernel - Re: Getting weird TPM error after rebasing my tree to security/next-general

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Date:   Thu, 31 Jan 2019 14:26:06 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        tomas.winkler@...el.com
Subject: Re: Getting weird TPM error after rebasing my tree to
 security/next-general

On Tue, Jan 29, 2019 at 03:20:16PM +0200, Jarkko Sakkinen wrote:
> 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@...ux.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).

I think I have found the root cause:

memcpy_fromio(&__rsp_pa, &priv->regs_t->ctrl_rsp_pa, 8);

This is from crb_map_io(). This should be read as quad word.

I'll change it to ioread64() and see what happens. I don't know why it
even has used memcpy_fromio() in the first place. I guess, when I first
implemented the driver, I used that for no logical reason, and it has
worked since up until now.

/Jarkko