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Date: Fri, 16 Apr 2021 15:14:56 -0700
From: Ira Weiny <ira.weiny@...el.com>
To: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>,
Dan Williams <dan.j.williams@...el.com>, x86@...nel.org,
linux-kernel@...r.kernel.org, Fenghua Yu <fenghua.yu@...el.com>,
linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH V6 00/10] PKS: Add Protection Key Supervisor support
On Thu, Apr 01, 2021 at 03:58:23PM -0700, 'Ira Weiny' wrote:
> From: Ira Weiny <ira.weiny@...el.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.
>
> 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 V5 [6]
> From Dave Hansen
> Remove 'we' from comments
>
> Changes from V4 [5]
> From kernel test robot <lkp@...el.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
>
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