[RFC PATCH v4 00/12] security: x86/sgx: SGX vs. LSM
Sean Christopherson
sean.j.christopherson at intel.com
Wed Jun 19 22:23:49 UTC 2019
For those of you whom I neglected to cc on v3, here's a quick recap:
My original plan was for my next RFC to be an implementation of Andy's
proposed "dynamic tracking" model, but I was completely flummoxed by the
auditing[1]. Cedric's RFC has the same auditing complexities, so I
I ended up back at the "make userspace state its intentions" approach.
There are no significant LSM changes in v4, e.g. a bug fix and some
renaming. I'm spinning v4 early to get the cc list correct, and also
because I'm about to disappear on vacation for two weeks.
Except for patch 12 (see below), the SGX changes have been fully tested,
including updating the kernel's selftest as well as my own fork of (an old
version of) Intel's SDK to use the new UAPI. The LSM changes have been
smoke tested, but I haven't actually configured AppArmor or SELinux to
verify the permissions work as intended.
Patches 1-3 are not directly related to LSM support. They're included
here as the actual LSM RFC patches are essentially untestable without
them, and so that the patches apply to Jarkko's tree. Ignore patches
1-3 unless you actually want to run code.
Patches 4-11 are the meat of the RFC.
Patch 12 is purely to show how we might implement SGX2 support. It's not
intended to be included in the initial upstreaming of SGX.
The full code is available at https://github.com/sean-jc/linux.git in
a few forms (tagged);
sgx-lsm-v4 - Jarkko's full tree plus patches 1-11
sgx-lsm-v4-eaug - Everything above plus patch 12
<boilerplate>
This series is a delta to Jarkko's ongoing SGX series and applies on
Jarkko's current master at https://github.com/jsakkine-intel/linux-sgx.git:
91f3aa6d241d ("docs: x86/sgx: Document the enclave API")
The basic gist of the approach is to track an enclave's page protections
separately from any vmas that map the page, and separate from the hardware
enforced protections. The SGX UAPI is modified to require userspace to
explicitly define the protections for each enclave page, i.e. the ioctl
to add pages to an enclave is extended to take PROT_{READ,WRITE,EXEC}
flags.
An enclave page's protections are the maximal protections that userspace
can use to map the page, e.g. mprotect() and mmap() are rejected if the
protections for the vma would be more permissible than those of the
associated enclave page.
Tracking protections for an enclave page (in additional to vmas) allows
SGX to invoke LSM upcalls while the enclave is being built. This is
critical to enabling LSMs to implement policies for enclave pages that
are functionally equivalent to existing policies for normal pages.
</boilerplate>
[1] https://lkml.kernel.org/r/20190614003759.GE18385@linux.intel.com
v4:
- Rename SGX__EXECMEM and SGX__EXECMOD to SGX__MAPWX and SGX_EXECDIRTY
respectively [Stephen].
- Fix an inverted check on IS_PRIVATE file check [Stephen].
- Take a '__u8 prot' in SGX_IOC_ENCLAVE_ADD_PAGE [Jarkko].
- Rebased to Jarkko's latest code base.
- Replace patch 1 with a variant that does encl_mm tracking via
mmu_notifier and SRCU. Not relevant for most people, but I wanted
to show the end state if we get rid of the per-vma tracking.
v3: https://patchwork.kernel.org/cover/11000601/
- Clear VM_MAY* flags instead of using .may_mprotect() to enforce
maximal enclave page protections.
- Update the SGX selftest to work with the new API.
- Rewrite SELinux code to use SGX specific permissions, with the goal
of addressing Andy's feedback regarding what people will actually
care about when it comes to SGX, e.g. add permissions for restricing
unmeasured code and stop trying to infer permissions from the source
of each enclave page.
- Add a (very minimal) AppArmor patch.
- Show line of sight to SGX2 support.
- Rebased to Jarkko's latest code base.
v2: https://lkml.kernel.org/r/20190606021145.12604-1-sean.j.christopherson@intel.com
- Dropped the patch(es) to extend the SGX UAPI to allow adding multiple
enclave pages in a single syscall [Jarkko].
- Reject ioctl() immediately on LSM denial [Stephen].
- Rework SELinux code to avoid checking EXEMEM multiple times [Stephen].
- Adding missing equivalents to existing selinux_file_protect() checks
[Stephen].
- Hold mmap_sem across copy_to_user() to prevent a TOCTOU race when
checking the source vma [Stephen].
- Stubify security_enclave_load() if !CONFIG_SECURITY [Stephen].
- Make flags a 32-bit field [Andy].
- Don't validate the SECINFO protection flags against the enclave
page's protection flags [Andy].
- Rename mprotect() hook to may_mprotect() [Andy].
- Test 'vma->vm_flags & VM_MAYEXEC' instead of manually checking for
a noexec path [Jarkko].
- Drop the SGX defined flags (use PROT_*) [Jarkko].
- Improve comments and changelogs [Jarkko].
v1: https://lkml.kernel.org/r/20190531233159.30992-1-sean.j.christopherson@intel.com
Sean Christopherson (12):
x86/sgx: Use mmu_notifier.release() instead of per-vma refcounting
x86/sgx: Do not naturally align MAP_FIXED address
selftests: x86/sgx: Mark the enclave loader as not needing an exec
stack
x86/sgx: Require userspace to define enclave pages' protection bits
x86/sgx: Enforce noexec filesystem restriction for enclaves
mm: Introduce vm_ops->may_mprotect()
LSM: x86/sgx: Introduce ->enclave_map() hook for Intel SGX
security/selinux: Require SGX_MAPWX to map enclave page WX
LSM: x86/sgx: Introduce ->enclave_load() hook for Intel SGX
security/selinux: Add enclave_load() implementation
security/apparmor: Add enclave_load() implementation
LSM: x86/sgx: Show line of sight to LSM support SGX2's EAUG
arch/x86/Kconfig | 2 +
arch/x86/include/uapi/asm/sgx.h | 6 +-
arch/x86/kernel/cpu/sgx/driver/ioctl.c | 69 ++++--
arch/x86/kernel/cpu/sgx/driver/main.c | 106 ++++++++-
arch/x86/kernel/cpu/sgx/encl.c | 277 ++++++++++++-----------
arch/x86/kernel/cpu/sgx/encl.h | 22 +-
arch/x86/kernel/cpu/sgx/reclaim.c | 71 ++----
include/linux/lsm_hooks.h | 20 ++
include/linux/mm.h | 2 +
include/linux/security.h | 18 ++
mm/mprotect.c | 15 +-
security/apparmor/include/audit.h | 2 +
security/apparmor/lsm.c | 14 ++
security/security.c | 12 +
security/selinux/hooks.c | 72 ++++++
security/selinux/include/classmap.h | 6 +-
tools/testing/selftests/x86/sgx/Makefile | 2 +-
tools/testing/selftests/x86/sgx/main.c | 32 ++-
18 files changed, 532 insertions(+), 216 deletions(-)
--
2.21.0
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