Re: [RFC PATCH v2 4/5] LSM: x86/sgx: Introduce ->enclave_load() hook for Intel SGX

From: Jarkko Sakkinen
Date: Mon Jun 10 2019 - 12:09:51 EST

On Wed, Jun 05, 2019 at 07:11:44PM -0700, Sean Christopherson wrote:
> enclave_load() is roughly analogous to the existing file_mprotect().
> Due to the nature of SGX and its Enclave Page Cache (EPC), all enclave
> VMAs are backed by a single file, i.e. /dev/sgx/enclave, that must be
> MAP_SHARED. Furthermore, all enclaves need read, write and execute
> VMAs. As a result, the existing/standard call to file_mprotect() does
> not provide any meaningful security for enclaves since an LSM can only
> deny/grant access to the EPC as a whole.
> security_enclave_load() is called when SGX is first loading an enclave
> page, i.e. copying a page from normal memory into the EPC. Although
> the prototype for enclave_load() is similar to file_mprotect(), e.g.
> SGX could theoretically use file_mprotect() and set reqprot=prot, a
> separate hook is desirable as the semantics of an enclave's protection
> bits are different than those of vmas, e.g. an enclave page tracks the
> maximal set of protections, whereas file_mprotect() operates on the
> actual protections being provided. In other words, LSMs will likely
> want to implement different policies for enclave page protections.
> Note, extensive discussion yielded no sane alternative to some form of
> SGX specific LSM hook[1].
> [1]
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>

4/5 and 5/5 should only be added after upstreaming SGX.