Re: [PATCH V4 15/31] x86/sgx: Support restricting of enclave page permissions

[Jarkko Sakkinen]

On Thu, 2022-04-14 at 14:19 +0300, Jarkko Sakkinen wrote:
> On Wed, 2022-04-13 at 14:10 -0700, Reinette Chatre wrote:
> > In the initial (SGX1) version of SGX, pages in an enclave need to be
> > created with permissions that support all usages of the pages, from the
> > time the enclave is initialized until it is unloaded. For example,
> > pages used by a JIT compiler or when code needs to otherwise be
> > relocated need to always have RWX permissions.
> > 
> > SGX2 includes a new function ENCLS[EMODPR] that is run from the kernel
> > and can be used to restrict the EPCM permissions of regular enclave
> > pages within an initialized enclave.
> > 
> > Introduce ioctl() SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS to support
> > restricting EPCM permissions. With this ioctl() the user specifies
> > a page range and the EPCM permissions to be applied to all pages in
> > the provided range. ENCLS[EMODPR] is run to restrict the EPCM
> > permissions followed by the ENCLS[ETRACK] flow that will ensure
> > no cached linear-to-physical address mappings to the changed
> > pages remain.
> > 
> > It is possible for the permission change request to fail on any
> > page within the provided range, either with an error encountered
> > by the kernel or by the SGX hardware while running
> > ENCLS[EMODPR]. To support partial success the ioctl() returns an
> > error code based on failures encountered by the kernel as well
> > as two result output parameters: one for the number of pages
> > that were successfully changed and one for the SGX return code.
> > 
> > The page table entry permissions are not impacted by the EPCM
> > permission changes. VMAs and PTEs will continue to allow the
> > maximum vetted permissions determined at the time the pages
> > are added to the enclave. The SGX error code in a page fault
> > will indicate if it was an EPCM permission check that prevented
> > an access attempt.
> > 
> > No checking is done to ensure that the permissions are actually
> > being restricted. This is because the enclave may have relaxed
> > the EPCM permissions from within the enclave without the kernel
> > knowing. An attempt to relax permissions using this call will
> > be ignored by the hardware.
> > 
> > Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> 
> Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

Also for this:

Tested-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

BR, Jarkko