by Michael Kerrisk (man-pages)

[permalink] [raw]

Subject: Re: [PATCH 00/32] x86: Memory Protection Keys (v7)

Hi Dave,

On 12/14/2015 08:05 PM, Dave Hansen wrote:
> Memory Protection Keys for User pages is a CPU feature which will
> first appear on Skylake Servers, but will also be supported on
> future non-server parts (there is also a QEMU implementation). It
> provides a mechanism for enforcing page-based protections, but
> without requiring modification of the page tables when an
> application changes protection domains. See the Documentation/
> patch for more details.

You've arbitrarily CCed this mail and one other patch in the
series to linux-api@. This makes the series hard to review
unless one is subscribed to the LKML firehose. Please, for
future iterations of this series, CC the entire patchset to
linux-api@.

Thanks,

Michael

> This set enables for two things in the end:
> 1. Allows "execute-only" memory
> 2. Enables KVM to run Protection-Key-enabled guests
>
> Changes from v6:
> * fix up ??'s showing up in in smaps' VmFlags field
> * added execute-only support
> * removed all the new syscalls from this set. We can discuss
> them in detail after this is merged.
>
> Changes from v5:
>
> * make types in read_pkru() u32's, not ints
> * rework VM_* bits to avoid using __ffsl() and clean up
> vma_pkey()
> * rework pte_allows_gup() to use p??_val() instead of passing
> around p{te,md,ud}_t types.
> * Fix up some inconsistent bool vs. int usage
> * corrected name of ARCH_VM_PKEY_FLAGS in patch description
> * remove NR_PKEYS... config option. Just define it directly
>
> Changes from v4:
>
> * Made "allow setting of XSAVE state" safe if we got preempted
> between when we saved our FPU state and when we restore it.
> (I would appreciate a look from Ingo on this patch).
> * Fixed up a few things from Thomas's latest comments: splt up
> siginfo in to x86 and generic, removed extra 'eax' variable
> in rdpkru function, reworked vm_flags assignment, reworded
> a comment in pte_allows_gup()
> * Add missing DISABLED/REQUIRED_MASK14 in cpufeature.h
> * Added comment about compile optimization in fault path
> * Left get_user_pages_locked() alone. Andrea thinks we need it.
>
> Changes from RFCv3:
>
> * Added 'current' and 'foreign' variants of get_user_pages() to
> help indicate whether protection keys should be enforced.
> Thanks to Jerome Glisse for pointing out this issue.
> * Added "allocation" and set/get system calls so that we can do
> management of proection keys in the kernel. This opens the
> door to use of specific protection keys for kernel use in the
> future, such as for execute-only memory.
> * Removed the kselftest code for the moment. It will be
> submitted separately.
>
> Thanks Ingo and Thomas for most of these):
> Changes from RFCv2 (Thanks Ingo and Thomas for most of these):
>
> * few minor compile warnings
> * changed 'nopku' interaction with cpuid bits. Now, we do not
> clear the PKU cpuid bit, we just skip enabling it.
> * changed __pkru_allows_write() to also check access disable bit
> * removed the unused write_pkru()
> * made si_pkey a u64 and added some patch description details.
> Also made it share space in siginfo with MPX and clarified
> comments.
> * give some real text for the Processor Trace xsave state
> * made vma_pkey() less ugly (and much more optimized actually)
> * added SEGV_PKUERR to copy_siginfo_to_user()
> * remove page table walk when filling in si_pkey, added some
> big fat comments about it being inherently racy.
> * added self test code
>
> This code is not runnable to anyone outside of Intel unless they
> have some special hardware or a fancy simulator. There is a qemu
> model to emulate the feature, but it is not currently implemented
> fully enough to be usable. If you are interested in running this
> for real, please get in touch with me. Hardware is available to a
> very small but nonzero number of people.
>
> This set is also available here:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/daveh/x86-pkeys.git pkeys-v018
>
> === diffstat ===
>
> Dave Hansen (32):
> mm, gup: introduce concept of "foreign" get_user_pages()
> x86, fpu: add placeholder for Processor Trace XSAVE state
> x86, pkeys: Add Kconfig option
> x86, pkeys: cpuid bit definition
> x86, pkeys: define new CR4 bit
> x86, pkeys: add PKRU xsave fields and data structure(s)
> x86, pkeys: PTE bits for storing protection key
> x86, pkeys: new page fault error code bit: PF_PK
> x86, pkeys: store protection in high VMA flags
> x86, pkeys: arch-specific protection bits
> x86, pkeys: pass VMA down in to fault signal generation code
> signals, pkeys: notify userspace about protection key faults
> x86, pkeys: fill in pkey field in siginfo
> x86, pkeys: add functions to fetch PKRU
> mm: factor out VMA fault permission checking
> x86, mm: simplify get_user_pages() PTE bit handling
> x86, pkeys: check VMAs and PTEs for protection keys
> mm: add gup flag to indicate "foreign" mm access
> x86, pkeys: optimize fault handling in access_error()
> x86, pkeys: differentiate instruction fetches
> x86, pkeys: dump PKRU with other kernel registers
> x86, pkeys: dump PTE pkey in /proc/pid/smaps
> x86, pkeys: add Kconfig prompt to existing config option
> x86, pkeys: actually enable Memory Protection Keys in CPU
> mm, multi-arch: pass a protection key in to calc_vm_flag_bits()
> x86, pkeys: add arch_validate_pkey()
> x86: separate out LDT init from context init
> x86, fpu: allow setting of XSAVE state
> x86, pkeys: allow kernel to modify user pkey rights register
> x86, pkeys: create an x86 arch_calc_vm_prot_bits() for VMA flags
> x86, pkeys: execute-only support
> x86, pkeys: Documentation
>
> Documentation/kernel-parameters.txt | 3 +
> Documentation/x86/protection-keys.txt | 27 +++
> arch/mips/mm/gup.c | 3 +-
> arch/powerpc/include/asm/mman.h | 5 +-
> arch/powerpc/include/asm/mmu_context.h | 12 ++
> arch/s390/include/asm/mmu_context.h | 12 ++
> arch/s390/mm/gup.c | 3 +-
> arch/sh/mm/gup.c | 2 +-
> arch/sparc/mm/gup.c | 2 +-
> arch/unicore32/include/asm/mmu_context.h | 12 ++
> arch/x86/Kconfig | 16 ++
> arch/x86/include/asm/cpufeature.h | 56 +++---
> arch/x86/include/asm/disabled-features.h | 13 ++
> arch/x86/include/asm/fpu/internal.h | 2 +
> arch/x86/include/asm/fpu/types.h | 12 ++
> arch/x86/include/asm/fpu/xstate.h | 4 +-
> arch/x86/include/asm/mmu_context.h | 85 ++++++++-
> arch/x86/include/asm/pgtable.h | 38 ++++
> arch/x86/include/asm/pgtable_types.h | 34 +++-
> arch/x86/include/asm/pkeys.h | 34 ++++
> arch/x86/include/asm/required-features.h | 5 +
> arch/x86/include/asm/special_insns.h | 22 +++
> arch/x86/include/uapi/asm/mman.h | 22 +++
> arch/x86/include/uapi/asm/processor-flags.h | 2 +
> arch/x86/kernel/cpu/common.c | 42 +++++
> arch/x86/kernel/fpu/core.c | 63 +++++++
> arch/x86/kernel/fpu/xstate.c | 185 +++++++++++++++++++-
> arch/x86/kernel/ldt.c | 4 +-
> arch/x86/kernel/process_64.c | 2 +
> arch/x86/kernel/setup.c | 9 +
> arch/x86/mm/Makefile | 2 +
> arch/x86/mm/fault.c | 171 +++++++++++++++---
> arch/x86/mm/gup.c | 46 +++--
> arch/x86/mm/mpx.c | 4 +-
> arch/x86/mm/pkeys.c | 101 +++++++++++
> drivers/char/agp/frontend.c | 2 +-
> drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 4 +-
> drivers/gpu/drm/i915/i915_gem_userptr.c | 2 +-
> drivers/gpu/drm/radeon/radeon_ttm.c | 4 +-
> drivers/gpu/drm/via/via_dmablit.c | 3 +-
> drivers/infiniband/core/umem.c | 2 +-
> drivers/infiniband/core/umem_odp.c | 8 +-
> drivers/infiniband/hw/mthca/mthca_memfree.c | 3 +-
> drivers/infiniband/hw/qib/qib_user_pages.c | 3 +-
> drivers/infiniband/hw/usnic/usnic_uiom.c | 2 +-
> drivers/iommu/amd_iommu_v2.c | 8 +-
> drivers/media/pci/ivtv/ivtv-udma.c | 4 +-
> drivers/media/pci/ivtv/ivtv-yuv.c | 10 +-
> drivers/media/v4l2-core/videobuf-dma-sg.c | 3 +-
> drivers/misc/sgi-gru/grufault.c | 3 +-
> drivers/scsi/st.c | 2 -
> drivers/staging/android/ashmem.c | 4 +-
> drivers/video/fbdev/pvr2fb.c | 4 +-
> drivers/virt/fsl_hypervisor.c | 5 +-
> fs/exec.c | 8 +-
> fs/proc/task_mmu.c | 14 ++
> include/asm-generic/mm_hooks.h | 12 ++
> include/linux/mm.h | 60 +++++--
> include/linux/mman.h | 6 +-
> include/linux/pkeys.h | 33 ++++
> include/uapi/asm-generic/siginfo.h | 17 +-
>
> Cc: [email protected]
> Cc: [email protected]
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--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

2016-03-29 09:26:27

by tip-bot for Vasyl Gomonovych

[permalink] [raw]

Subject: [tip:x86/urgent] x86/mm/pkeys: Add missing Documentation

Commit-ID: 591b1d8d86074ac3a3163d89bcfe7b232cf83902
Gitweb: http://git.kernel.org/tip/591b1d8d86074ac3a3163d89bcfe7b232cf83902
Author: Dave Hansen <[email protected]>
AuthorDate: Mon, 14 Dec 2015 11:06:34 -0800
Committer: Ingo Molnar <[email protected]>
CommitDate: Tue, 29 Mar 2016 11:21:17 +0200

x86/mm/pkeys: Add missing Documentation

Stefan Richter noticed that the X86_INTEL_MEMORY_PROTECTION_KEYS option
in arch/x86/Kconfig references Documentation/x86/protection-keys.txt,
but the file does not exist.

This is a patch merging mishap: the final (v8) version of the pkeys
series did not include the documentation patch 32 and v7 included.
Add it now.

Reported-by: Stefan Richter <[email protected]>
Signed-off-by: Dave Hansen <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
[ Added changelog. ]
Signed-off-by: Ingo Molnar <[email protected]>

Signed-off-by: Ingo Molnar <[email protected]>
---
Documentation/x86/protection-keys.txt | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)

diff --git a/Documentation/x86/protection-keys.txt b/Documentation/x86/protection-keys.txt
new file mode 100644
index 0000000..c281ded
--- /dev/null
+++ b/Documentation/x86/protection-keys.txt
@@ -0,0 +1,27 @@
+Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU feature
+which will be found on future Intel CPUs.
+
+Memory Protection Keys provides a mechanism for enforcing page-based
+protections, but without requiring modification of the page tables
+when an application changes protection domains. It works by
+dedicating 4 previously ignored bits in each page table entry to a
+"protection key", giving 16 possible keys.
+
+There is also a new user-accessible register (PKRU) with two separate
+bits (Access Disable and Write Disable) for each key. Being a CPU
+register, PKRU is inherently thread-local, potentially giving each
+thread a different set of protections from every other thread.
+
+There are two new instructions (RDPKRU/WRPKRU) for reading and writing
+to the new register. The feature is only available in 64-bit mode,
+even though there is theoretically space in the PAE PTEs. These
+permissions are enforced on data access only and have no effect on
+instruction fetches.
+
+=========================== Config Option ===========================
+
+This config option adds approximately 1.5kb of text. and 50 bytes of
+data to the executable. A workload which does large O_DIRECT reads
+of holes in XFS files was run to exercise get_user_pages_fast(). No
+performance delta was observed with the config option
+enabled or disabled.