On Thu, May 30, 2019 at 11:01 AM Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote: > > On Thu, May 30, 2019 at 09:14:10AM -0700, Andy Lutomirski wrote: > > On Thu, May 30, 2019 at 8:04 AM Stephen Smalley <sds@xxxxxxxxxxxxx> wrote: > > > > > > On 5/30/19 10:31 AM, Andy Lutomirski wrote: > > > > Hi all- > > > > > > > > After an offline discussion with Sean yesterday, here are some updates > > > > to the user API parts of my proposal. > > > > > > > > Unfortunately, Sean convinced me that MAXPERM doesn't work the way I > > > > described it because, for SGX2, the enclave loader won't know at load > > > > time whether a given EAUG-ed page will ever be executed. So here's an > > > > update. > > > > > > > > First, here are the requrements as I see them, where EXECUTE, EXECMOD, > > > > and EXECMEM could be substituted with other rules at the LSM's > > > > discretion: > > > > > > > > - You can create a WX or RWX mapping if and only if you have EXECMEM. > > > > > > > > - To create an X mapping of an enclave page that has ever been W, you > > > > need EXECMOD. > > > > > > EXECMOD to what file? The enclave file from which the page's content > > > originated, the sigstruct file, or /dev/sgx/enclave? > > > > I leave that decision to you :) The user should need permission to do > > an execmod thing on an enclave, however that wants to be encoded. > > But that decision dictates how the SGX API handles sigstruct. If LSMs > want to associate EXECMOD with sigstruct, then SGX needs to take sigstruct > early and hold a reference to the file for the lifetime of the enclave. > And if we're going to do that, the whole approach of inheriting > permissions from source VMAs becomes unnecessary complexity. > > > > > > > > - To create an X mapping of an enclave page that came from EADD, you > > > > need EXECUTE on the source file. Optionally, we could also permit > > > > this if you have EXECMOD. > > > > > > What is the "source file" i.e. the target of the check? Enclave file, > > > sigstruct file, or /dev/sgx/enclave? > > > > Enclave file -- that is, the file backing the vma from which the data is loaded. > > It wasn't explicitly called out in Andy's proposal(s), but the idea is > that the SGX driver would effectively inherit permissions from the source > VMA (EADD needs a source for the initial value of the encave page). I actually meant for it to *not* work like this. I don't want the source VMA to have to be VM_EXEC. I think the LSM should just check permissions on ->vm_file.
