Re: [PATCH] x86/sgx: Fix ELDU MAC failures

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Fri, 2019-08-23 at 16:39 +0300, Jarkko Sakkinen wrote:
> On Fri, 2019-08-23 at 16:35 +0300, Jarkko Sakkinen wrote:
> > On Thu, 2019-08-22 at 19:00 -0700, Sean Christopherson wrote:
> > > Revert a change that directly propagates the page type from SECINFO into
> > > encl_page->desc.  encl_page->desc is a packed value, jamming the SECINFO
> > > page_type sets bits that are intended for other uses.
> > > 
> > > Specifically, bits 11:3 are used to store the VA offset when a page is
> > > swapped out and are available for other uses when the page is resident
> > > in the EPC.  To allow overloading bits 11:3, the VA offset is cleared at
> > > ELDU and so is not explicitly cleared at EWB, e.g. the VA offset is OR'd
> > > into encl_page->desc.  As a result, a subsequent ELDU gets a MAC failure
> > > due to loading the wrong VA offset.
> > > 
> > > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > > ---
> > >  arch/x86/kernel/cpu/sgx/driver/ioctl.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/x86/kernel/cpu/sgx/driver/ioctl.c b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> > > index 85e36e530baf..355ce967a77f 100644
> > > --- a/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> > > +++ b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> > > @@ -140,7 +140,8 @@ static struct sgx_encl_page *sgx_encl_page_alloc(struct sgx_encl *encl,
> > >  		return ERR_PTR(-ENOMEM);
> > >  
> > >  	encl_page->desc = addr;
> > > -	encl_page->desc |= page_type;
> > > +	if (page_type == SGX_SECINFO_TCS)
> > > +		encl_page->desc |= SGX_ENCL_PAGE_TCS;
> > >  	encl_page->encl = encl;
> > 
> > Oops. How embrassing from my side. Please also ignore my original review
> > comment about unreadability. The parameter type was right and everything
> > was right. I was just blind for a while.
> > 
> > This is exactly how it should be e.g. no boolean parameter. I think with
> > most of this kind of APIs we should follow a patttern the API takes PT
> > and the function does whatever encoding we have.
> 
> In any case the issue is fixed now on my tree and I also rewrote commit
> message for the driver.

The stress test that I've been using is temporarily broken ATM so could not
exercise the code path.

/Jarkko