Re: [PATCH v2 0/3] x86/sgx: eextend ioctl

[Jethro Beekman <jethro@fortanix.com>]

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On 2021-04-14 12:52, Jarkko Sakkinen wrote:
> On Mon, Apr 12, 2021 at 10:59:56AM +0200, Raoul Strackx wrote:
>> Creation of an SGX enclave consists of three steps. First, a new enclave
>> environment is created by the ECREATE leaf function. Some enclave settings
>> are specified at this step by passing an SGX Enclave Control Structure
>> (SECS) that contains the enclave MRENCLAVE, MRSIGNER, etc. This
>> instruction also starts a cryptographic log of the enclave being built.
>> (This log should eventually result in the MRENCLAVE.) Second, pages are
>> added to the enclave. The EADD leaf function copies 4KB data to an empty
>> EPC page. The cryptographic log records (among other properties) the
>> location and access rights of the page being added. It _does not_ include
>> an entry of the page content. When the enclave writer wishes to ensure the
>> content of (a part of) the enclave page as well, she must use the EEXTEND
>> leaf function. Extending the enclave cryptographic log can only be done
>> per 256 bytes. Extending the log with a full 4K page thus requires 16
>> invocations of the EEXTEND leaf function. It is however up to the enclave
>> developer to decide if and how enclave memory is added to the 
>> cryptographic log. EEXTEND functions may be issued only for relevant parts
>> of an enclave page, may happen only after all pages have been added, and
>> so on. Finally, the enclave is finalized by the EINIT leaf function. Any
>> new invocations of the EADD or EEXTEND leaf functions will result in a
>> fault. With EINIT a number of checks are performed as well. The 
>> cryptographic hash of the final cryptographic log is compared to the
>> MRENCLAVE field of the SECS structure passed to the ECREATE leaf function
>> (see step one). The signature (MRSIGNER) over this MRENCLAVE is verified
>> as well. When all checks pass, the enclave loading is complete and it
>> enters the executable state.
> 
> Who do you expect to read this paragraph, seriously?

What do you mean? There was a request for more architectural details in the cover letter.

> 
>> The SGX driver currently only supports extending the cryptographic log as
>> part of the EADD leaf function and _must_ cover complete 4K pages.
>> Enclaves not constructed within these constraints, currently cannot be
>> loaded on the Linux platform. Trying to do so will result in a different
>> cryptographic log; the MRENCLAVE specified at enclave creation time will
>> not match the cryptographic log kept by the processor and EINIT will fail.
>> This poses practical problems:
>> - The current driver does not fully support all possible SGXv1 enclaves.
>>   It creates a separation between enclaves that run everywhere and
>>   enclaves that run everywhere, except on Linux. This includes enclaves
>>   already in use on other systems today.
>> - It limits optimizations loaders are able to perform. For example, by
>>   only measuring relevant parts of enclave pages, load time can be
>>   minimized.
>>
>> This patch set adds a new ioctl to enable userspace to execute EEXTEND
>> leaf functions per 256 bytes of enclave memory. With this patch in place,
>> Linux will be able to build all valid SGXv1 enclaves.
>>
>> See additional discussion at:
>> https://lore.kernel.org/linux-sgx/20200220221038.GA26618@linux.intel.com/
>> T/#m93597f53d354201e72e26d93a968f167fcdf5930
>>
>>
>> Raoul Strackx (3):
>>   x86/sgx: Adding eextend ioctl
>>   x86/sgx: Fix compatibility issue with OPENSSL < 1.1.0
>>   x86/sgx: eextend ioctl selftest
>>
>>  arch/x86/include/uapi/asm/sgx.h         | 11 +++++
>>  arch/x86/kernel/cpu/sgx/ioctl.c         | 81 ++++++++++++++++++++++++++++-----
>>  tools/testing/selftests/sgx/defines.h   |  1 +
>>  tools/testing/selftests/sgx/load.c      | 57 +++++++++++++++++++----
>>  tools/testing/selftests/sgx/main.h      |  1 +
>>  tools/testing/selftests/sgx/sigstruct.c | 43 ++++++++---------
>>  6 files changed, 154 insertions(+), 40 deletions(-)
>>
>> -- 
>> 2.7.4
>>
>>
> 
> /Jarkko
> 

--
Jethro Beekman | Fortanix


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