Re: [PATCH 1/4] x86/sgx: Ensure enclave state is visible before marking it created

[Sean Christopherson <sean.j.christopherson@intel.com>]

On Tue, Aug 27, 2019 at 02:20:44PM +0300, Jarkko Sakkinen wrote:
> On Mon, Aug 26, 2019 at 05:11:25PM -0700, Sean Christopherson wrote:
> > Add a memory barrier pair to ensure all enclave state is visible in
> > memory prior to SGX_ENCL_CREATED being set.  Without the barries, adding
> > pages and/or initializing the enclaves could theoretically consume stale
> > data.
> > 
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > ---
> >  arch/x86/kernel/cpu/sgx/ioctl.c | 16 +++++++++++++---
> >  1 file changed, 13 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> > index 911ff3b0f061..7134d68aecb3 100644
> > --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> > +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> > @@ -163,6 +163,15 @@ static struct sgx_encl_page *sgx_encl_page_alloc(struct sgx_encl *encl,
> >  	return encl_page;
> >  }
> >  
> > +static bool is_encl_created(struct sgx_encl *encl)
> > +{
> > +	bool created = encl->flags & SGX_ENCL_CREATED;
> > +
> > +	/* Pairs with smp_wmb() in sgx_encl_create(). */
> > +	smp_rmb();
> > +	return created;
> > +}
> 
> what if you just convert the flags to atomic_t? That would fix this
> issue and would prevent analogous issues from occuring.

I thought about that too, but originally discarded the idea because I
was worried doing so would negatively impact the other uses of flags.
After actually implementing the change, I think the positives outweigh
the negatives, so I'll send a v2 with this suggestion.