RE: [PATCH v20 00/28] Intel SGX1 support
From: Xing, Cedric
Date: Fri May 10 2019 - 14:58:03 EST
> ELF files are explicitly designed such that you can map them (with mmap)
> in 4096-byte chunks. However, sometimes there's overlap and you will
> sometimes see that a particular offset is mapped twice because the first
> half of the page in the file belongs to an RX range and the second half
> to an R-only range. Also, ELF files don't (normally) describe stack,
> heap, etc. which you do need for enclaves.
You have probably misread my email. By mmap(), I meant the enclave file would be mapped via *multiple* mmap() calls, in the same way as what dlopen() would do in loading regular shared object. The intention here is to make the enclave file subject to the same checks as regular shared objects.
The other enclave components (e.g. TCS, heap, stack, etc.) will be created from writable pages within the calling process's address space as before. Similar to heaps/stacks in a regular process, those components don't have to be backed by disk files.
The core idea is for SGX driver to "copy" not only the content but also permissions from a source page to the target EPC page. Given the existence of the source page, it can be concluded that the combination of content and permissions of that page has passed all IMA/LSM checks applicable to that page, hence "copying" that page to EPC with the same (or less) permission is *not* a circumvention of IMA/LSM policies.