[PATCH] powerpc/64s: Disable STRICT_KERNEL_RWX

[PATCH] powerpc/64s: Disable STRICT_KERNEL_RWX

[Michael Ellerman]

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>
---
 arch/powerpc/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 924c541a9260..d13b5328ca10 100644
--- 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
-- 
2.25.1

Re: [PATCH] powerpc/64s: Disable STRICT_KERNEL_RWX

[Michael Ellerman]

On Wed, 20 May 2020 23:36:05 +1000, Michael Ellerman wrote:
> 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.
> 
> [...]

Applied to powerpc/fixes.

[1/1] powerpc/64s: Disable STRICT_KERNEL_RWX
      https://git.kernel.org/powerpc/c/8659a0e0efdd975c73355dbc033f79ba3b31e82c

cheers