On Thu, Apr 01, 2021 at 03:58:23PM -0700, 'Ira Weiny' wrote:
From: Ira Weiny ira.weiny@intel.com
Introduce a new page protection mechanism for supervisor pages, Protection Key Supervisor (PKS).
Is there any feedback on this series?
Perhaps I should ping for specific feedback or an ack? Maybe an ack from x86/mm?
Ira
Generally PKS enables protections on 'domains' of supervisor pages to limit supervisor mode access to pages beyond the normal paging protections. PKS works in a similar fashion to user space pkeys, PKU. As with PKU, supervisor pkeys are checked in addition to normal paging protections and Access or Writes can be disabled via a MSR update without TLB flushes when permissions change.
Also like PKU, a page mapping is assigned to a domain by setting pkey bits in the page table entry for that mapping.
Access is controlled through a PKRS register which is updated via WRMSR/RDMSR.
XSAVE is not supported for the PKRS MSR. Therefore the implementation saves/restores the MSR across context switches and during exceptions. Nested exceptions are supported by each exception getting a new PKS state.
For consistent behavior with current paging protections, pkey 0 is reserved and configured to allow full access via the pkey mechanism, thus preserving the default paging protections on mappings with the default pkey value of 0.
Other keys, (1-15) are allocated by an allocator which prepares us for key contention from day one. Kernel users should be prepared for the allocator to fail either because of key exhaustion or due to PKS not being supported on the CPU instance.
The following are key attributes of PKS.
- Fast switching of permissions 1a) Prevents access without page table manipulations 1b) No TLB flushes required
- Works on a per thread basis
PKS is available with 4 and 5 level paging. Like PKRU it consumes 4 bits from the PTE to store the pkey within the entry.
All code to support PKS is configured via ARCH_ENABLE_SUPERVISOR_PKEYS which is designed to only be turned on when a user is configured on in the kernel. Those users must depend on ARCH_HAS_SUPERVISOR_PKEYS to properly work with other architectures which do not yet support PKS.
Originally this series was submitted as part of a large patch set which converted the kmap call sites.[1]
Many follow on discussions revealed a few problems. The first of which was that some callers leak a kmap mapping across threads rather than containing it to a critical section. Attempts were made to see if these 'global kmaps' could be supported.[2] However, supporting global kmaps had many problems. Work is being done in parallel on converting as many kmap calls to the new kmap_local_page().[3]
Changes from V5 [6] From Dave Hansen Remove 'we' from comments
Changes from V4 [5] From kernel test robot lkp@intel.com Fix i386 build: pks_init_task not found Move MSR_IA32_PKRS and INIT_PKRS_VALUE into patch 5 where they are first 'used'. (Technically nothing is 'used' until the final test patch. But review wise this is much cleaner.) From Sean Christoperson Add documentation details on what happens if the pkey is violated Change cpu_feature_enabled to be in WARN_ON check Clean up commit message of patch 6
[1] https://lore.kernel.org/lkml/20201009195033.3208459-1-ira.weiny@intel.com/
[2] https://lore.kernel.org/lkml/87mtycqcjf.fsf@nanos.tec.linutronix.de/
[3] https://lore.kernel.org/lkml/20210128061503.1496847-1-ira.weiny@intel.com/ https://lore.kernel.org/lkml/20210210062221.3023586-1-ira.weiny@intel.com/ https://lore.kernel.org/lkml/20210205170030.856723-1-ira.weiny@intel.com/ https://lore.kernel.org/lkml/20210217024826.3466046-1-ira.weiny@intel.com/
[4] https://lore.kernel.org/lkml/20201106232908.364581-1-ira.weiny@intel.com/
[5] https://lore.kernel.org/lkml/20210322053020.2287058-1-ira.weiny@intel.com/
[6] https://lore.kernel.org/lkml/20210331191405.341999-1-ira.weiny@intel.com/
Fenghua Yu (1): x86/pks: Add PKS kernel API
Ira Weiny (9): x86/pkeys: Create pkeys_common.h x86/fpu: Refactor arch_set_user_pkey_access() for PKS support x86/pks: Add additional PKEY helper macros x86/pks: Add PKS defines and Kconfig options x86/pks: Add PKS setup code x86/fault: Adjust WARN_ON for PKey fault x86/pks: Preserve the PKRS MSR on context switch x86/entry: Preserve PKRS MSR across exceptions x86/pks: Add PKS test code
Documentation/core-api/protection-keys.rst | 112 +++- arch/x86/Kconfig | 1 + arch/x86/entry/calling.h | 26 + arch/x86/entry/common.c | 57 ++ arch/x86/entry/entry_64.S | 22 +- arch/x86/entry/entry_64_compat.S | 6 +- arch/x86/include/asm/cpufeatures.h | 1 + arch/x86/include/asm/disabled-features.h | 8 +- arch/x86/include/asm/msr-index.h | 1 + arch/x86/include/asm/pgtable.h | 15 +- arch/x86/include/asm/pgtable_types.h | 12 + arch/x86/include/asm/pkeys.h | 4 + arch/x86/include/asm/pkeys_common.h | 34 + arch/x86/include/asm/pks.h | 54 ++ arch/x86/include/asm/processor-flags.h | 2 + arch/x86/include/asm/processor.h | 47 +- arch/x86/include/uapi/asm/processor-flags.h | 2 + arch/x86/kernel/cpu/common.c | 2 + arch/x86/kernel/fpu/xstate.c | 22 +- arch/x86/kernel/head_64.S | 7 +- arch/x86/kernel/process.c | 3 + arch/x86/kernel/process_64.c | 2 + arch/x86/mm/fault.c | 30 +- arch/x86/mm/pkeys.c | 218 +++++- include/linux/pgtable.h | 4 + include/linux/pkeys.h | 34 + kernel/entry/common.c | 14 +- lib/Kconfig.debug | 11 + lib/Makefile | 3 + lib/pks/Makefile | 3 + lib/pks/pks_test.c | 694 ++++++++++++++++++++ mm/Kconfig | 5 + tools/testing/selftests/x86/Makefile | 3 +- tools/testing/selftests/x86/test_pks.c | 149 +++++ 34 files changed, 1527 insertions(+), 81 deletions(-) create mode 100644 arch/x86/include/asm/pkeys_common.h create mode 100644 arch/x86/include/asm/pks.h create mode 100644 lib/pks/Makefile create mode 100644 lib/pks/pks_test.c create mode 100644 tools/testing/selftests/x86/test_pks.c
-- 2.28.0.rc0.12.gb6a658bd00c9