[PATCH V3 00/30] x86/sgx and selftests/sgx: Support SGX2

Reinette Chatre
2022-04-04T22:02:03Z

V2: https://lore.kernel.org/lkml/cover.1644274683.git.reinette.chatre@intel.com/

Changes since V2 that directly impact user space:
- Maximum allowed permissions of dynamically added pages is RWX,
previously limited to RW. (Jarkko)
Dynamically added pages are initially created with architecturally
limited EPCM permissions of RW. mmap() and mprotect() of these pages
with RWX permissions would no longer be blocked by SGX driver. PROT_EXEC
on dynamically added pages will be possible after running ENCLU[EMODPE]
from within the enclave with appropriate VMA permissions.

- The kernel no longer attempts to track the EPCM runtime permissions. (Jarkko)
Consequences are:
- Kernel does not modify PTEs to follow EPCM permissions. User space
will receive #PF with SGX error code in cases where the V2
implementation would have resulted in regular (non-SGX) page fault
error code.
- SGX_IOC_ENCLAVE_RELAX_PERMISSIONS is removed. This ioctl() was used
to clear PTEs after permissions were modified from within the enclave
and ensure correct PTEs are installed. Since PTEs no longer track
EPCM permissions the changes in EPCM permissions would not impact PTEs.
As long as new permissions are within the maximum vetted permissions
(vm_max_prot_bits) only ENCLU[EMODPE] from within enclave is needed,
as accompanied by appropriate VMA permissions.

- struct sgx_enclave_restrict_perm renamed to
sgx_enclave_restrict_permissions (Jarkko)

- struct sgx_enclave_modt renamed to struct sgx_enclave_modify_type
to be consistent with the verbose naming of other SGX uapi structs.

Details about changes since V2 that do not directly impact user space:
- Kernel no longer tracks the runtime EPCM permissions with the aim of
installing accurate PTEs. (Jarkko)
- In support of this change the following patches were removed:
Documentation/x86: Document SGX permission details
x86/sgx: Support VMA permissions more relaxed than enclave permissions
x86/sgx: Add pfn_mkwrite() handler for present PTEs
x86/sgx: Add sgx_encl_page->vm_run_prot_bits for dynamic permission changes
x86/sgx: Support relaxing of enclave page permissions
- No more handling of scenarios where VMA permissions may be more
relaxed than what the EPCM allows. Enclaves are not prevented
from accessing such pages and the EPCM permissions are entrusted
to control access as supported by the SGX error code in page faults.
- No more explicit setting of protection bits in page fault handler.
Protection bits are inherited from VMA similar to SGX1 support.

- Selftest patches are moved to the end of the series. (Jarkko)

- New patch contributed by Jarkko to avoid duplicated code:
x86/sgx: Export sgx_encl_page_alloc()

- New patch separating changes from existing patch. (Jarkko)
x86/sgx: Export sgx_encl_{grow,shrink}()

- New patch to keep one required benefit from the (now removed) kernel
EPCM permission tracking:
x86/sgx: Support loading enclave page without VMA permissions check

- Updated cover letter to reflect architecture changes.

- Many smaller changes, please refer to individual patches.

V1: https://lore.kernel.org/linux-sgx/cover.1638381245.git.reinette.chatre@intel.com/

Changes since V1 that directly impact user space:
- SGX2 permission changes changed from a single ioctl() named
SGX_IOC_PAGE_MODP to two new ioctl()s:
SGX_IOC_ENCLAVE_RELAX_PERMISSIONS and
SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS, supported by two different
parameter structures (SGX_IOC_ENCLAVE_RELAX_PERMISSIONS does
not support a result output parameter) (Jarkko).

User space flow impact: After user space runs ENCLU[EMODPE] it
needs to call SGX_IOC_ENCLAVE_RELAX_PERMISSIONS to have PTEs
updated. Previously running SGX_IOC_PAGE_MODP in this scenario
resulted in EPCM.PR being set but calling
SGX_IOC_ENCLAVE_RELAX_PERMISSIONS will not result in EPCM.PR
being set anymore and thus no need for an additional
ENCLU[EACCEPT].

- SGX_IOC_ENCLAVE_RELAX_PERMISSIONS and
SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS
obtain new permissions from secinfo as parameter instead of
the permissions directly (Jarkko).

- ioctl() supporting SGX2 page type change is renamed from
SGX_IOC_PAGE_MODT to SGX_IOC_ENCLAVE_MODIFY_TYPE (Jarkko).

- SGX_IOC_ENCLAVE_MODIFY_TYPE obtains new page type from secinfo
as parameter instead of the page type directly (Jarkko).

- ioctl() supporting SGX2 page removal is renamed from
SGX_IOC_PAGE_REMOVE to SGX_IOC_ENCLAVE_REMOVE_PAGES (Jarkko).

- All ioctl() parameter structures have been renamed as a result of the
ioctl() renaming:
SGX_IOC_ENCLAVE_RELAX_PERMISSIONS => struct sgx_enclave_relax_perm
SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS => struct sgx_enclave_restrict_perm
SGX_IOC_ENCLAVE_MODIFY_TYPE => struct sgx_enclave_modt
SGX_IOC_ENCLAVE_REMOVE_PAGES => struct sgx_enclave_remove_pages

Changes since V1 that do not directly impact user space:
- Number of patches in series increased from 25 to 32 primarily because
of splitting the original submission:
- Wrappers for the new SGX2 functions are introduced in three separate
patches replacing the original "x86/sgx: Add wrappers for SGX2
functions"
(Jarkko).
- Moving and renaming sgx_encl_ewb_cpumask() is done with two patches
replacing the original "x86/sgx: Use more generic name for enclave
cpumask function" (Jarkko).
- Support for SGX2 EPCM permission changes is split into two ioctls(),
one for relaxing and one for restricting permissions, each introduced
by a new patch replacing the original "x86/sgx: Support enclave page
permission changes" (Jarkko).
- Extracted code used by existing ioctls() for usage by new ioctl()s
into a new utility in new patch "x86/sgx: Create utility to validate
user provided offset and length" (Dave did not specifically ask for
this but it addresses his review feedback).
- Two new Documentation patches to support the SGX2 work
("Documentation/x86: Introduce enclave runtime management") and
a dedicated section on the enclave permission management
("Documentation/x86: Document SGX permission details") (Andy).
- Most patches were reworked to improve the language by:
* aiming to refer to exact item instead of English rephrasing (Jarkko).
* use ioctl() instead of ioctl throughout (Dave).
* Use "relaxed" instead of "exceed" when referring to permissions
(Dave).
- Improved documentation with several additions to
Documentation/x86/sgx.rst.
- Many smaller changes, please refer to individual patches.

Hi Everybody,

The current Linux kernel support for SGX includes support for SGX1 that
requires that an enclave be created with properties that accommodate all
usages over its (the enclave's) lifetime. This includes properties such
as permissions of enclave pages, the number of enclave pages, and the
number of threads supported by the enclave.

Consequences of this requirement to have the enclave be created to
accommodate all usages include:
* pages needing to support relocated code are required to have RWX
permissions for their entire lifetime,
* an enclave needs to be created with the maximum stack and heap
projected to be needed during the enclave's entire lifetime which
can be longer than the processes running within it,
* an enclave needs to be created with support for the maximum number
of threads projected to run in the enclave.

Since SGX1 a few more functions were introduced, collectively called
SGX2, that support modifications to an initialized enclave. Hardware
supporting these functions are already available as listed on
https://github.com/ayeks/SGX-hardware

This series adds support for SGX2, also referred to as Enclave Dynamic
Memory Management (EDMM). This includes:

* Support modifying EPCM permissions of regular enclave pages belonging
to an initialized enclave. Only permission restriction is supported
via a new ioctl() SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS. Relaxing of
EPCM permissions can only be done from within the enclave with
ENCLU[EMODPE].

* Support dynamic addition of regular enclave pages to an initialized
enclave. At creation new pages are architecturally limited to RW EPCM
permissions but will be accessible with PROT_EXEC after the enclave
runs ENCLU[EMODPE] to relax EPCM permissions to RWX.
Pages are dynamically added to an initialized enclave from the SGX
page fault handler.

* Support expanding an initialized enclave to accommodate more threads.
More threads can be accommodated by an enclave with the addition of
Thread Control Structure (TCS) pages that is done by changing the
type of regular enclave pages to TCS pages using a new ioctl()
SGX_IOC_ENCLAVE_MODIFY_TYPE.

* Support removing regular and TCS pages from an initialized enclave.
Removing pages is accomplished in two stages as supported by two new
ioctl()s SGX_IOC_ENCLAVE_MODIFY_TYPE (same ioctl() as mentioned in
previous bullet) and SGX_IOC_ENCLAVE_REMOVE_PAGES.

* Tests covering all the new flows, some edge cases, and one
comprehensive stress scenario.

No additional work is needed to support SGX2 in a virtualized
environment. All tests included in this series passed when run from
a guest as tested with the recent QEMU release based on 6.2.0
that supports SGX.

Patches 1 to 13 prepare the existing code for SGX2 support by
introducing the SGX2 functions, refactoring code, and tracking enclave
page types.

Patches 14 through 20 enable the SGX2 features and include a
Documentation patch.

Patches 21 through 30 test several scenarios of all the enabled
SGX2 features.

This series is based on v5.17 with the following fixes that have already
been merged for inclusion into v5.18-rc1. These can be obtained from the
x86/sgx branch of tip.git.

commit 2d03861e0d1d ("selftests/sgx: Fix NULL-pointer-dereference upon early test failure")
commit fff36bcbfde1 ("selftests/sgx: Do not attempt enclave build without valid enclave")
commit 2db703fc3b15 ("selftests/sgx: Ensure enclave data available during debug print")
commit 5626de65f97a ("selftests/sgx: Remove extra newlines in test output")
commit b06e15ebd5bf ("selftests/x86: Add validity check and allow field splitting")
commit 6170abb21e23 ("selftests/sgx: Treat CC as one argument")

Your feedback will be greatly appreciated.

Regards,

Reinette

Jarkko Sakkinen (1):
x86/sgx: Export sgx_encl_page_alloc()

Reinette Chatre (29):
x86/sgx: Add short descriptions to ENCLS wrappers
x86/sgx: Add wrapper for SGX2 EMODPR function
x86/sgx: Add wrapper for SGX2 EMODT function
x86/sgx: Add wrapper for SGX2 EAUG function
x86/sgx: Support loading enclave page without VMA permissions check
x86/sgx: Export sgx_encl_ewb_cpumask()
x86/sgx: Rename sgx_encl_ewb_cpumask() as sgx_encl_cpumask()
x86/sgx: Move PTE zap code to new sgx_zap_enclave_ptes()
x86/sgx: Make sgx_ipi_cb() available internally
x86/sgx: Create utility to validate user provided offset and length
x86/sgx: Keep record of SGX page type
x86/sgx: Export sgx_encl_{grow,shrink}()
x86/sgx: Support restricting of enclave page permissions
x86/sgx: Support adding of pages to an initialized enclave
x86/sgx: Tighten accessible memory range after enclave initialization
x86/sgx: Support modifying SGX page type
x86/sgx: Support complete page removal
x86/sgx: Free up EPC pages directly to support large page ranges
Documentation/x86: Introduce enclave runtime management section
selftests/sgx: Add test for EPCM permission changes
selftests/sgx: Add test for TCS page permission changes
selftests/sgx: Test two different SGX2 EAUG flows
selftests/sgx: Introduce dynamic entry point
selftests/sgx: Introduce TCS initialization enclave operation
selftests/sgx: Test complete changing of page type flow
selftests/sgx: Test faulty enclave behavior
selftests/sgx: Test invalid access to removed enclave page
selftests/sgx: Test reclaiming of untouched page
selftests/sgx: Page removal stress test

Documentation/x86/sgx.rst | 15 +
arch/x86/include/asm/sgx.h | 8 +
arch/x86/include/uapi/asm/sgx.h | 62 +
arch/x86/kernel/cpu/sgx/encl.c | 330 +++-
arch/x86/kernel/cpu/sgx/encl.h | 13 +-
arch/x86/kernel/cpu/sgx/encls.h | 33 +
arch/x86/kernel/cpu/sgx/ioctl.c | 668 +++++++-
arch/x86/kernel/cpu/sgx/main.c | 70 +-
arch/x86/kernel/cpu/sgx/sgx.h | 3 +
tools/testing/selftests/sgx/defines.h | 23 +
tools/testing/selftests/sgx/load.c | 41 +
tools/testing/selftests/sgx/main.c | 1456 +++++++++++++++++
tools/testing/selftests/sgx/main.h | 1 +
tools/testing/selftests/sgx/test_encl.c | 68 +
.../selftests/sgx/test_encl_bootstrap.S | 6 +
15 files changed, 2675 insertions(+), 122 deletions(-)

base-commit: f443e374ae131c168a065ea1748feac6b2e76613
prerequisite-patch-id: 986260c8bc4255eb61e2c4afa88d2b723e376423
prerequisite-patch-id: ba014a99fced2b57d5d9e2dfb9d80ddf4333c13e
prerequisite-patch-id: 65cbb72889b6353a5639b984615d12019136b270
prerequisite-patch-id: e3296a2f0345a77c8a7ca91f76697ae2e1dca21f
prerequisite-patch-id: 0e792adec49b53020ee788fd0126e8f015ff483d
prerequisite-patch-id: b8685cf66d49f89ed7444feafa0129aa6144a163
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2.25.1