On Fri, May 17, 2019 at 11:04:22AM -0700, Linus Torvalds wrote: > On Fri, May 17, 2019 at 10:55 AM Sean Christopherson > <sean.j.christopherson@xxxxxxxxx> wrote: > > > > In this snippet, IS_PRIVATE() is true for anon inodes, false for > > /dev/sgx/enclave. Because EPC memory is always shared, SELinux will never > > check PROCESS__EXECMEM for mprotect() on/dev/sgx/enclave. > > Why _does_ the memory have to be shared? Shared mmap() is > fundamentally less secure than private mmap, since by definition it > means "oh, somebody else has access to it too and might modify it > under us". > > Why does the SGX logic care about things like that? Normal executables > are just private mappings of an underlying file, I'm not sure why the > SGX interface has to have that shared thing, and why the interface has > to have a device node in the first place when you have system calls > for setup anyway. > > So why don't the system calls just work on perfectly normal anonymous > mmap's? Why a device node, and why must it be shared to begin with? I agree that conceptually EPC is private memory, but because EPC is managed as a separate memory pool, SGX tags it VM_PFNMAP and manually inserts PFNs, i.e. EPC effectively it gets classified as IO memory. And vmf_insert_pfn_prot() doesn't like writable private IO mappings: BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
