Re: [PATCH] x86/sgx: Remove PROT_NONE branch from sgx_encl_may_map().

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

On Tue, Mar 31, 2020 at 12:13:36AM +0300, Jarkko Sakkinen wrote:
> On Mon, Mar 30, 2020 at 09:54:52PM +0300, Jarkko Sakkinen wrote:
> > sgx_encl_may_map() always succeeding when PROT_NONE is given is not that
> > useful behaviour as one can just well as do an anonymous mapping as
> > demonstrated by the change in this patch to the test program. As a
> > consequence, remove the special case.
> > 
> > Pratically any possible way to make sure that you don't overwrite anything
> > useful in the memory, should be fine. MAP_FIXED does not care what's
> > underneath (if you want't it to care you ought to use
> > MAP_FIXED_NO_REPLACE).
> > 
> > After this change, the selftest run called sgx_mmap() only three times
> > (TCS, text, data) instead of four.
> > 
> >         test_sgx-1811  [002] ....   586.907585: sgx_mmap <-mmap_region
> >         test_sgx-1811  [002] ....   586.911752: sgx_mmap <-mmap_region
> >         test_sgx-1811  [002] ....   586.911756: sgx_mmap <-mmap_region
> > 
> > This also gives more angles to segregate enclave building and mapping as
> > the mmap()'s need to be applied only when the enclave is fully built:
> > 
> > Cc: luto@kernel.org
> > Cc: Haitao Huang <haitao.huang@linux.intel.com>
> > Cc: Sean Christopherson <sean.j.christopherson@intel.com>
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> 
> Sean, would be cool if you can try this out soonish because I'm
> building on top of this.

Two and a half weeks is soonish, right?

Anyways, finally tested this, no issues.  Just to be different than the
selftest, I used MAP_PRIVATE instead of MAP_SHARED along with MAP_ANONYMOUS
in my test code.