powerpc/64s: Disable STRICT_KERNEL_RWX

Several strange crashes have been eventually traced back to
STRICT_KERNEL_RWX and its interaction with code patching.

Various paths in our ftrace, kprobes and other patching code need to
be hardened against patching failures, otherwise we can end up running
with partially/incorrectly patched ftrace paths, kprobes or jump
labels, which can then cause strange crashes.

Although fixes for those are in development, they're not -rc material.

There also seem to be problems with the underlying strict RWX logic,
which needs further debugging.

So for now disable STRICT_KERNEL_RWX on 64-bit to prevent people from
enabling the option and tripping over the bugs.

Fixes: 1e0fc9d1eb2b ("powerpc/Kconfig: Enable STRICT_KERNEL_RWX for some configs")
Cc: stable@vger.kernel.org # v4.13+
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200520133605.972649-1-mpe@ellerman.id.au

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 924c541..d13b532 100644 (file)
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -130,7 +130,7 @@ config PPC
        select ARCH_HAS_PTE_SPECIAL
        select ARCH_HAS_MEMBARRIER_CALLBACKS
        select ARCH_HAS_SCALED_CPUTIME          if VIRT_CPU_ACCOUNTING_NATIVE && PPC_BOOK3S_64
-       select ARCH_HAS_STRICT_KERNEL_RWX       if ((PPC_BOOK3S_64 || PPC32) && !HIBERNATION)
+       select ARCH_HAS_STRICT_KERNEL_RWX       if (PPC32 && !HIBERNATION)
        select ARCH_HAS_TICK_BROADCAST          if GENERIC_CLOCKEVENTS_BROADCAST
        select ARCH_HAS_UACCESS_FLUSHCACHE
        select ARCH_HAS_UACCESS_MCSAFE          if PPC64