[PATCH v8 0/3] x86/sgx: fine grained SGX MCA behavior

Zhiquan Li
2022-09-13T15:47:21Z

V7: https://lore.kernel.org/linux-sgx/YxEyRT2SbfBdYNfm@kernel.org/T/#t

Changes since V7:
- Enrich the motivation for renaming in commit message of patch 01 with
the explanation from Kai.
- Add Acked-by from Jarkko.
Link: https://lore.kernel.org/linux-sgx/YxEyRT2SbfBdYNfm@kernel.org/T/#mc1c93e7d9643588b27cefa9540f988a070469b5b
- Add Acked-by from Kai Huang at patch 01.

V6: https://lore.kernel.org/linux-sgx/20220826160503.1576966-1-zhiquan1.li@intel.com/T/#t

Changes since V6:
- Revise the commit message of patch 01 suggested by Jarkko.
- Fix build warning due to type changes.

V5: https://lore.kernel.org/linux-sgx/Yrf27fugD7lkyaek@kernel.org/T/#t

Changes since V5:
- Rename the 'owner' field as 'encl_owner' and update the references
as a separate patch.
- To prevent casting the 'encl_owner' field, introduce a union with
another field - "vepc_vaddr", suggested by Dave Hansen.
- Clean up the commit message of patch 02 suggested by Dave Hansen.
- Remove patch 03 unless we have better reason to keep it.
- Add Reviewed-by from Jarkko.
Link: https://lore.kernel.org/linux-sgx/Yrf27fugD7lkyaek@kernel.org/T/#m379d00fc7f1d43726a42b3884637532061a8c0d1

V4: https://lore.kernel.org/linux-sgx/20220608032654.1764936-1-zhiquan1.li@intel.com/T/#t

Changes since V4:
- Switch the order of the two variables at patch 02 so all of variables
are in reverse Christmas style.
- Do not initialize 'ret' because it will be overridden by the return
value of force_sig_mceerr() unconditionally.
- Add Co-developed-by and Signed-off-by from Cathy Zhang at patch 01.
- Add Acked-by from Kai Huang at patch 01.

V3: https://lore.kernel.org/linux-sgx/41704e5d4c03b49fcda12e695595211d950cfb08.camel@kernel.org/T/#t

Changes since V3:
- Take the definition of EPC page flag SGX_EPC_PAGE_KVM_GUEST from
Cathy Zhang's third patch of SGX rebootless recovery patch set but
discard irrelevant portion, since it might need some time to re-forge
and these are two different features.
Link: https://lore.kernel.org/linux-sgx/41704e5d4c03b49fcda12e695595211d950cfb08.camel@kernel.org/T/#m9782d23496cacecb7da07a67daa79f4b322ae170

V2: https://lore.kernel.org/linux-sgx/694234d7-6a0d-e85f-f2f9-e52b4a61e1ec@intel.com/T/#t

Changes since V2:
- Repurpose the owner field as the virtual address of virtual EPC page
- Remove struct sgx_vepc_page and relevant code.
- Remove patch 01 as the changes are not necessary in new design.
- Rework patch 02 suggested by Jarkko.
- Adapt patch 03 and 04 since struct sgx_vepc_page was discarded.
- Replace EPC page flag SGX_EPC_PAGE_IS_VEPC with
SGX_EPC_PAGE_KVM_GUEST as they are duplicated.
Link: https://lore.kernel.org/linux-sgx/eb95b32ecf3d44a695610cf7f2816785@intel.com/T/#u

V1: https://lore.kernel.org/linux-sgx/443cb425-009c-2784-56f4-5e707122de76@intel.com/T/#t

Changes since V1:
- Updated cover letter and commit messages, added valuable
information from Jarkko, Tony and Kai's comments.
- Added documentations for struct struct sgx_vepc and
struct sgx_vepc_page.

Hi everyone,

This series contains a few patches to fine grained SGX MCA behavior.
Today, if a guest accesses an SGX EPC page with memory failure,
the kernel behavior will kill the entire guest. This blast radius is
too large. It would be idea to kill only the SGX application inside
the guest.

To fix this, send a SIGBUS to host userspace (like QEMU) which can
follow up by injecting a #MC to the guest.
However, when a page triggers a machine check, it only reports the
PFN. But in order to inject #MC into hypervisor, the virtual address
is required. The 'encl_owner' field is useless in virtualization
case, then repurpose it as 'vepc_vaddr' - the virtual address of the
virtual EPC page for such case so that arch_memory_failure() can easily
retrieve it.

Suppose an enclave is shared by multiple processes, when an enclave
page triggers a machine check, the enclave will be disabled so that
it couldn't be entered again. Killing other processes with the same
enclave mapped would perhaps be overkill, but they are going to find
that the enclave is "dead" next time they try to use it. Thanks for
Jarkko’s head up and Tony’s clarification on this point.
Unlike host enclaves, virtual EPC instance cannot be shared by multiple
VMs. It is because how enclaves are created is totally up to the guest.
Sharing virtual EPC instance will be very likely to unexpectedly break
enclaves in all VMs.

SGX virtual EPC driver doesn't explicitly prevent virtual EPC instance
being shared by multiple VMs via fork(). However KVM doesn't support
running a VM across multiple mm structures, and the de facto userspace
hypervisor (Qemu) doesn't use fork() to create a new VM, so in practice
this should not happen.

This series is based on tip/x86/sgx.

Tests:
1. MCE injection test for SGX in VM.
As we expected, the application was killed and VM was alive.
2. Kernel selftest/sgx: PASS
3. Internal SGX stress test: PASS
4. kmemleak test: No memory leakage detected.

Much appreciate your feedback.

Best Regards,
Zhiquan

Zhiquan Li (3):
x86/sgx: Rename the owner field of struct sgx_epc_page as encl_owner
x86/sgx: Introduce union with vepc_vaddr field for virtualization case
x86/sgx: Fine grained SGX MCA behavior for virtualization

arch/x86/kernel/cpu/sgx/main.c | 48 +++++++++++++++++++++++++---------
arch/x86/kernel/cpu/sgx/sgx.h | 8 +++++-
arch/x86/kernel/cpu/sgx/virt.c | 4 ++-
3 files changed, 46 insertions(+), 14 deletions(-)

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2.25.1