On Fri, Oct 09, 2020 at 12:42:49PM -0700, 'Ira Weiny' wrote: > From: Ira Weiny <ira.weiny@xxxxxxxxx> > > 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@xxxxxxxxx/ Trusted Keys: https://lore.kernel.org/lkml/20201009201410.3209180-1-ira.weiny@xxxxxxxxx/ 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@xxxxxxxxx/ > [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 >
