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| author | Michael Ellerman <mpe@ellerman.id.au> | 2019-04-18 16:51:24 +1000 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2019-04-21 23:06:02 +1000 |
| commit | 890274c2dc4c0a57ae5a12d6a76fa6d05b599d98 (patch) | |
| tree | c014ea05d98098873ad3787a3b324f3bb9c55618 /arch/powerpc/platforms | |
| parent | ef296729b735e083d8919e76ac213b8ff237eb78 (diff) | |
| download | blackbird-op-linux-890274c2dc4c0a57ae5a12d6a76fa6d05b599d98.tar.gz blackbird-op-linux-890274c2dc4c0a57ae5a12d6a76fa6d05b599d98.zip | |
powerpc/64s: Implement KUAP for Radix MMU
Kernel Userspace Access Prevention utilises a feature of the Radix MMU
which disallows read and write access to userspace addresses. By
utilising this, the kernel is prevented from accessing user data from
outside of trusted paths that perform proper safety checks, such as
copy_{to/from}_user() and friends.
Userspace access is disabled from early boot and is only enabled when
performing an operation like copy_{to/from}_user(). The register that
controls this (AMR) does not prevent userspace from accessing itself,
so there is no need to save and restore when entering and exiting
userspace.
When entering the kernel from the kernel we save AMR and if it is not
blocking user access (because eg. we faulted doing a user access) we
reblock user access for the duration of the exception (ie. the page
fault) and then restore the AMR when returning back to the kernel.
This feature can be tested by using the lkdtm driver (CONFIG_LKDTM=y)
and performing the following:
# (echo ACCESS_USERSPACE) > [debugfs]/provoke-crash/DIRECT
If enabled, this should send SIGSEGV to the thread.
We also add paranoid checking of AMR in switch and syscall return
under CONFIG_PPC_KUAP_DEBUG.
Co-authored-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/platforms')
| -rw-r--r-- | arch/powerpc/platforms/Kconfig.cputype | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype index 60371784c9f1..5e53b9fd62aa 100644 --- a/arch/powerpc/platforms/Kconfig.cputype +++ b/arch/powerpc/platforms/Kconfig.cputype @@ -327,6 +327,7 @@ config PPC_RADIX_MMU depends on PPC_BOOK3S_64 select ARCH_HAS_GIGANTIC_PAGE if (MEMORY_ISOLATION && COMPACTION) || CMA select PPC_HAVE_KUEP + select PPC_HAVE_KUAP default y help Enable support for the Power ISA 3.0 Radix style MMU. Currently this @@ -370,6 +371,13 @@ config PPC_KUAP If you're unsure, say Y. +config PPC_KUAP_DEBUG + bool "Extra debugging for Kernel Userspace Access Protection" + depends on PPC_HAVE_KUAP && PPC_RADIX_MMU + help + Add extra debugging for Kernel Userspace Access Protection (KUAP) + If you're unsure, say N. + config ARCH_ENABLE_HUGEPAGE_MIGRATION def_bool y depends on PPC_BOOK3S_64 && HUGETLB_PAGE && MIGRATION |
