[PATCH v4 00/13] selftests/sgx: Fix compilation errors

[Jo Van Bulck <jo.vanbulck@cs.kuleuven.be>]

Hi,

This is the fourth iteration of a patch series to ensure that all SGX selftests
succeed when compiling with optimizations (as tested with -O{0,1,2,3,s} for
both gcc 11.3.0 and clang 14.0.0). The aim of the patches is to avoid reliance
on undefined, compiler-specific behavior that can make the test results
fragile.

This series appends 4 new commits compared to the previous series (do let me
know if appending commits to this series is not the preferred way to handle
these?):

1. Another fix for possibly uninitialized pointer dereferences in
   encl_get_entry. Note that this was only brought up as a compiler warning
   when compiling the loader itself (i.e., not only the enclave) with
   optimizations. Also not that the uninitialized pointers shouldn't show up
   for "well-formed" enclave ELF files that properly contain a symbol table
   section, but I considered it is nevertheless good practice to harden the
   code against this (unlikely) case.
2. Split off the ".dyn*" and ".gnu.hash" discarding in a separate commit, as
   suggested by Kay [1].
3. Split off the removal of the redundant push/pop pair in a separate commit,
   as suggested by Kai [2].
4. Remove all (incomplete) CPU register cleansing assembly code on enclave
   exit, reflecting earlier discussions that highlight that the test enclave
   should *not* be confused with exemplary, security-hardened enclave code, and
   in line with Dave's suggestion to make the test enclave more *obviously*
   insecure [3].

If useful, I can also include an elementary wrapper shell script to compile and
run the tests for different compilers (gcc/clang) and optimization levels.
Reference output below:

.. Testing gcc   -O0    [OK]
.. Testing gcc   -O1    [OK]
.. Testing gcc   -O2    [OK]
.. Testing gcc   -O3    [OK]
.. Testing gcc   -Os    [OK]
.. Testing gcc   -Ofast [OK]
.. Testing gcc   -Og    [OK]
.. Testing clang -O0    [OK]
.. Testing clang -O1    [OK]
.. Testing clang -O2    [OK]
.. Testing clang -O3    [OK]
.. Testing clang -Os    [OK]
.. Testing clang -Ofast [OK]
.. Testing clang -Og    [OK]

Changelog
---------

v4
  - Remove redundant -nostartfiles compiler flag (Jarkko)
  - Split dynamic symbol table removal in separate commit (Kai)
  - Split redundant push/pop elimination in separate commit (Kai)
  - Remove (incomplete) register cleansing on enclave exit
  - Fix possibly uninitialized pointer dereferences in load.c

v3
  - Refactor encl_op_array declaration and indexing (Jarkko)
  - Annotate encl_buffer with "used" attribute (Kai)
  - Split encl_buffer size and placement commits (Kai)

v2
  - Add additional check for NULL pointer (Kai)
  - Refine to produce proper static-pie executable
  - Fix linker script assertions
  - Specify memory clobber for inline asm instead of volatile (Kai)
  - Clarify why encl_buffer non-static (Jarkko, Kai)
  - Clarify -ffreestanding (Jarkko)

References
----------

[1] https://lore.kernel.org/all/90ad8638bc1c26505e33b3f436fdbc22c8d74ba9.camel@intel.com/
[2] https://lore.kernel.org/all/71ad6389da7db8541dada0276db33f98e2a4fdcf.camel@intel.com/
[3] https://lore.kernel.org/all/da0cfb1e-e347-f7f2-ac72-aec0ee0d867d@intel.com/

Best,
Jo


Jo Van Bulck (13):
  selftests/sgx: Fix uninitialized pointer dereference in error path
  selftests/sgx: Produce static-pie executable for test enclave
  selftests/sgx: Handle relocations in test enclave
  selftests/sgx: Fix linker script asserts
  selftests/sgx: Include memory clobber for inline asm in test enclave
  selftests/sgx: Ensure test enclave buffer is entirely preserved
  selftests/sgx: Ensure expected location of test enclave buffer
  selftests/sgx: Separate linker options
  selftests/sgx: Specify freestanding environment for enclave
    compilation
  selftests/sgx: Fix uninitialized pointer dereferences
  selftests/sgx: Discard unsupported ELF sections
  selftests/sgx: Remove redundant enclave base address save/restore
  selftests/sgx: Remove incomplete ABI sanitization code in test enclave

 tools/testing/selftests/sgx/Makefile          | 14 ++--
 tools/testing/selftests/sgx/defines.h         |  2 +
 tools/testing/selftests/sgx/load.c            |  9 ++-
 tools/testing/selftests/sgx/sigstruct.c       |  5 +-
 tools/testing/selftests/sgx/test_encl.c       | 65 ++++++++++++-------
 tools/testing/selftests/sgx/test_encl.lds     | 10 +--
 .../selftests/sgx/test_encl_bootstrap.S       | 28 +++-----
 7 files changed, 76 insertions(+), 57 deletions(-)

-- 
2.25.1