Re: [PATCH V3 00/10] PKS: Add Protection Keys Supervisor (PKS) support V3

Ira Weiny
2020-12-07T22:14:36Z

Thomas,

Is there any chance of this landing before the kmap stuff gets sorted out?

It would be nice to have this in 5.11 to build off of.

Ira

On Fri, Nov 06, 2020 at 03:28:58PM -0800, 'Ira Weiny' wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> Changes from V2 [4]
> Rebased on tip-tree/core/entry
> From Thomas Gleixner
> Address bisectability
> Drop Patch:
> x86/entry: Move nmi entry/exit into common code
> From Greg KH
> Remove WARN_ON's
> From Dan Williams
> Add __must_check to pks_key_alloc()
> New patch: x86/pks: Add PKS defines and config options
> Split from Enable patch to build on through the series
> Fix compile errors
>
> Changes from V1
> Rebase to TIP master; resolve conflicts and test
> Clean up some kernel docs updates missed in V1
> Add irqentry_state_t kernel doc for PKRS field
> Removed redundant irq_state->pkrs
> This is only needed when we add the global state and somehow
> ended up in this patch series. That will come back when we add
> the global functionality in.
> From Thomas Gleixner
> Update commit messages
> Add kernel doc for struct irqentry_state_t
> From Dave Hansen add flags to pks_key_alloc()
>
> Changes from RFC V3[3]
> Rebase to TIP master
> Update test error output
> Standardize on 'irq_state' for state variables
> From Dave Hansen
> Update commit messages
> Add/clean up comments
> Add X86_FEATURE_PKS to disabled-features.h and remove some
> explicit CONFIG checks
> Move saved_pkrs member of thread_struct
> Remove superfluous preempt_disable()
> s/irq_save_pks/irq_save_set_pks/
> Ensure PKRS is not seen in faults if not configured or not
> supported
> s/pks_mknoaccess/pks_mk_noaccess/
> s/pks_mkread/pks_mk_readonly/
> s/pks_mkrdwr/pks_mk_readwrite/
> Change pks_key_alloc return to -EOPNOTSUPP when not supported
> From Peter Zijlstra
> Clean up Attribution
> Remove superfluous preempt_disable()
> Add union to differentiate exit_rcu/lockdep use in
> irqentry_state_t
> From Thomas Gleixner
> Add preliminary clean up patch and adjust series as needed
>
>
> Introduce a new page protection mechanism for supervisor pages, Protection Key
> Supervisor (PKS).
>
> 2 use cases for PKS are being developed, trusted keys and PMEM. Trusted keys
> is a newer use case which is still being explored. PMEM was submitted as part
> of the RFC (v2) series[1]. However, since then it was found that some callers
> of kmap() require a global implementation of PKS. Specifically some users of
> kmap() expect mappings to be available to all kernel threads. While global use
> of PKS is rare it needs to be included for correctness. Unfortunately the
> kmap() updates required a large patch series to make the needed changes at the
> various kmap() call sites so that patch set has been split out. Because the
> global PKS feature is only required for that use case it will be deferred to
> that set as well.[2] This patch set is being submitted as a precursor to both
> of the use cases.
>
> For an overview of the entire PKS ecosystem, a git tree including this series
> and 2 proposed use cases can be found here:
>
> https://lore.kernel.org/lkml/20201009195033.3208459-1-ira.weiny@intel.com/
> https://lore.kernel.org/lkml/20201009201410.3209180-1-ira.weiny@intel.com/
>
>
> PKS enables protections on 'domains' of supervisor pages to limit supervisor
> mode access to those 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
> arch and/or 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.
>
>
> [1] https://lore.kernel.org/lkml/20200717072056.73134-1-ira.weiny@intel.com/
> [2] https://lore.kernel.org/lkml/20201009195033.3208459-2-ira.weiny@intel.com/
> [3] https://lore.kernel.org/lkml/20201009194258.3207172-1-ira.weiny@intel.com/
> [4] https://lore.kernel.org/lkml/20201102205320.1458656-1-ira.weiny@intel.com/
>
> Fenghua Yu (2):
> x86/pks: Add PKS kernel API
> x86/pks: Enable Protection Keys Supervisor (PKS)
>
> Ira Weiny (8):
> x86/pkeys: Create pkeys_common.h
> x86/fpu: Refactor arch_set_user_pkey_access() for PKS support
> x86/pks: Add PKS defines and Kconfig options
> x86/pks: Preserve the PKRS MSR on context switch
> x86/entry: Pass irqentry_state_t by reference
> x86/entry: Preserve PKRS MSR across exceptions
> x86/fault: Report the PKRS state on fault
> x86/pks: Add PKS test code
>
> Documentation/core-api/protection-keys.rst | 103 ++-
> arch/x86/Kconfig | 1 +
> arch/x86/entry/common.c | 46 +-
> arch/x86/include/asm/cpufeatures.h | 1 +
> arch/x86/include/asm/disabled-features.h | 8 +-
> arch/x86/include/asm/idtentry.h | 25 +-
> arch/x86/include/asm/msr-index.h | 1 +
> arch/x86/include/asm/pgtable.h | 13 +-
> arch/x86/include/asm/pgtable_types.h | 12 +
> arch/x86/include/asm/pkeys.h | 15 +
> arch/x86/include/asm/pkeys_common.h | 40 ++
> arch/x86/include/asm/processor.h | 18 +-
> arch/x86/include/uapi/asm/processor-flags.h | 2 +
> arch/x86/kernel/cpu/common.c | 15 +
> arch/x86/kernel/cpu/mce/core.c | 4 +-
> arch/x86/kernel/fpu/xstate.c | 22 +-
> arch/x86/kernel/kvm.c | 6 +-
> arch/x86/kernel/nmi.c | 4 +-
> arch/x86/kernel/process.c | 26 +
> arch/x86/kernel/traps.c | 21 +-
> arch/x86/mm/fault.c | 87 ++-
> arch/x86/mm/pkeys.c | 196 +++++-
> include/linux/entry-common.h | 31 +-
> include/linux/pgtable.h | 4 +
> include/linux/pkeys.h | 24 +
> kernel/entry/common.c | 44 +-
> lib/Kconfig.debug | 12 +
> lib/Makefile | 3 +
> lib/pks/Makefile | 3 +
> lib/pks/pks_test.c | 692 ++++++++++++++++++++
> mm/Kconfig | 2 +
> tools/testing/selftests/x86/Makefile | 3 +-
> tools/testing/selftests/x86/test_pks.c | 66 ++
> 33 files changed, 1410 insertions(+), 140 deletions(-)
> create mode 100644 arch/x86/include/asm/pkeys_common.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