[RFC PATCH v1 0/3] An alternative __vdso_sgx_enter_enclave() to allow enclave/host parameter passing using untrusted stack

[Cedric Xing]

The current proposed __vdso_sgx_enter_enclave() requires enclaves to preserve
%rsp, which prohibits enclaves from allocating space on the untrusted stack.
However, there are existing enclaves (e.g. those built with current Intel SGX
SDK libraries) relying on the untrusted stack for passing parameters to
untrusted functions (aka. o-calls), which requires allocating space on the
untrusted stack by enclaves. And given its simplicity and convenience, it could
be desired by future SGX applications as well.

This patchset introduces a new ABI for __vdso_sgx_enter_enclave() to anchor its
stack frame on %rbp (instead of %rsp), so as to allow enclaves to "push" onto
the untrusted stack by decrementing the untrusted %rsp. Additionally, this new
__vdso_sgx_enter_enclave() will take one more parameter - a callback function,
to be invoked upon all enclave exits (both AEX and normal exits). The
callback function will be given the value of %rsp left off by the enclave,
so that data "pushed" by the enclave (if any) could be addressed/accessed.
Please note that the callback function is optional, and if not supplied
(i.e. null), __vdso_sgx_enter_enclave() will just return (i.e. behave the
same as the current implementation) after the enclave exits (or AEX
due to exceptions).

The SGX selftest is augmented to test out the new callback interface, and to
serve as a simple example to showcase how to use the callback interface in
practice.

Reference:
* This patchset is based upon SGX1 patch v20
  (https://lkml.org/lkml/2019/4/17/344) by Jarkko Sakkinen

Cedric Xing (3):
  selftests/x86: Fixed Makefile for SGX selftest
  x86/vdso: Modify __vdso_sgx_enter_enclave() to allow parameter passing
    on untrusted stack
  selftests/x86: Augment SGX selftest to test new
    __vdso_sgx_enter_enclave() and its callback interface

 arch/x86/entry/vdso/vsgx_enter_enclave.S   | 156 ++++++++++++---------
 arch/x86/include/uapi/asm/sgx.h            |  14 +-
 tools/testing/selftests/x86/Makefile       |  12 +-
 tools/testing/selftests/x86/sgx/Makefile   |  45 +++---
 tools/testing/selftests/x86/sgx/main.c     | 123 +++++++++++++---
 tools/testing/selftests/x86/sgx/sgx_call.S |  40 +++++-
 6 files changed, 264 insertions(+), 126 deletions(-)

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2.17.1