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Date: Fri, 9 Oct 2020 13:18:24 -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: x86@...nel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
Dan Williams <dan.j.williams@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Fenghua Yu <fenghua.yu@...el.com>, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC V3 0/9] PKS: Add Protection Keys Supervisor (PKS)
support RFC v3
On Fri, Oct 09, 2020 at 12:42:49PM -0700, 'Ira Weiny' wrote:
> From: Ira Weiny <ira.weiny@...el.com>
>
> This RFC series has been reviewed by Dave Hansen.
>
> 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.
RFC patch sets for these use cases have also been posted:
PMEM:
https://lore.kernel.org/lkml/20201009195033.3208459-1-ira.weiny@intel.com/
Trusted Keys:
https://lore.kernel.org/lkml/20201009201410.3209180-1-ira.weiny@intel.com/
Ira
> 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 the 2 use cases can be found here:
>
> https://github.com/weiny2/linux-kernel/tree/pks-rfc-v3
>
>
> 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://github.com/weiny2/linux-kernel/commit/f10abb0f0d7b4e14f03fc8890313a5830cde1e49
> and a testing patch
> https://github.com/weiny2/linux-kernel/commit/2a8e0fc7654a7c69b243d628f63b01ff26a5a797
>
>
> Fenghua Yu (3):
> x86/fpu: Refactor arch_set_user_pkey_access() for PKS support
> x86/pks: Enable Protection Keys Supervisor (PKS)
> x86/pks: Add PKS kernel API
>
> Ira Weiny (6):
> x86/pkeys: Create pkeys_common.h
> 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 | 102 ++-
> arch/x86/Kconfig | 1 +
> arch/x86/entry/common.c | 57 +-
> arch/x86/include/asm/cpufeatures.h | 1 +
> arch/x86/include/asm/idtentry.h | 29 +-
> 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 | 36 +
> arch/x86/include/asm/processor.h | 13 +
> arch/x86/include/uapi/asm/processor-flags.h | 2 +
> arch/x86/kernel/cpu/common.c | 17 +
> arch/x86/kernel/cpu/mce/core.c | 4 +
> arch/x86/kernel/fpu/xstate.c | 22 +-
> arch/x86/kernel/kvm.c | 4 +-
> arch/x86/kernel/nmi.c | 7 +-
> arch/x86/kernel/process.c | 21 +
> arch/x86/kernel/traps.c | 21 +-
> arch/x86/mm/fault.c | 86 ++-
> arch/x86/mm/pkeys.c | 188 +++++-
> include/linux/entry-common.h | 19 +-
> include/linux/pgtable.h | 4 +
> include/linux/pkeys.h | 23 +-
> kernel/entry/common.c | 28 +-
> lib/Kconfig.debug | 12 +
> lib/Makefile | 3 +
> lib/pks/Makefile | 3 +
> lib/pks/pks_test.c | 690 ++++++++++++++++++++
> mm/Kconfig | 2 +
> tools/testing/selftests/x86/Makefile | 3 +-
> tools/testing/selftests/x86/test_pks.c | 65 ++
> 32 files changed, 1376 insertions(+), 128 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
>
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