[V5,00/10] PKS: Add Protection Key Supervisor support

Message

Ira Weiny March 31, 2021, 7:13 p.m. UTC

From: Ira Weiny <[e-mail]>

Introduce a new page protection mechanism for supervisor pages, Protection Key
Supervisor (PKS).

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.

	1) Fast switching of permissions
		1a) Prevents access without page table manipulations
		1b) No TLB flushes required
	2) 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 V4 [5]
	From kernel test robot <[e-mail]>
		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
	Fix some checkpatch errors


[1] https://lore.kernel.org/lkml/[e-mail]/

[2] https://lore.kernel.org/lkml/[e-mail]/

[3] https://lore.kernel.org/lkml/[e-mail]/
    https://lore.kernel.org/lkml/[e-mail]/
    https://lore.kernel.org/lkml/[e-mail]/
    https://lore.kernel.org/lkml/[e-mail]/

[4] https://lore.kernel.org/lkml/[e-mail]/

[5] https://lore.kernel.org/lkml/[e-mail]/


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                     |  58 ++
 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              |  10 +-
 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                         |  31 +-
 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                          | 693 ++++++++++++++++++++
 mm/Kconfig                                  |   5 +
 tools/testing/selftests/x86/Makefile        |   3 +-
 tools/testing/selftests/x86/test_pks.c      | 150 +++++
 34 files changed, 1528 insertions(+), 77 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