Re: [PATCH v14 3/9] powerpc/modules: Make module_alloc() Strict Module RWX aware

Christophe Leroy [off-list ref] writes:

Le 17/05/2021 à 13:01, Michael Ellerman a écrit :

quoted

Jordan Niethe [off-list ref] writes:

quoted

On Mon, May 17, 2021 at 4:37 PM Christophe Leroy
[off-list ref] wrote:

quoted

Le 17/05/2021 à 05:28, Jordan Niethe a écrit :

quoted

Make module_alloc() use PAGE_KERNEL protections instead of
PAGE_KERNEL_EXEX if Strict Module RWX is enabled.

Signed-off-by: Jordan Niethe <redacted>
---
v14: - Split out from powerpc: Set ARCH_HAS_STRICT_MODULE_RWX
       - Add and use strict_module_rwx_enabled() helper
---
   arch/powerpc/include/asm/mmu.h | 5 +++++
   arch/powerpc/kernel/module.c   | 4 +++-
   2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
index 607168b1aef4..7710bf0cbf8a 100644
--- a/arch/powerpc/include/asm/mmu.h
+++ b/arch/powerpc/include/asm/mmu.h

@@ -357,6 +357,11 @@ static inline bool strict_kernel_rwx_enabled(void)
       return false;
   }
   #endif
+
+static inline bool strict_module_rwx_enabled(void)
+{
+     return IS_ENABLED(CONFIG_STRICT_MODULE_RWX) && strict_kernel_rwx_enabled();
+}

Looking at arch/Kconfig, I have the feeling that it is possible to select CONFIG_STRICT_MODULE_RWX
without selecting CONFIG_STRICT_KERNEL_RWX.

In that case, strict_kernel_rwx_enabled() will return false.

quoted

Ok, if someone did that currently it would break things, e.g. code
patching. I think it should it be made impossible to
CONFIG_STRICT_MODULE_RWX without CONFIG_STRICT_KERNEL_RWX?

Yeah I don't see any reason to support that combination.

We should be moving to a world where both are on by default, or in fact
are always enabled.

Would it work if we add the following in arch/powerpc/Kconfig ? :

	select STRICT_KERNEL_RWX if STRICT_MODULE_RWX

There should be no dependency issue as powerpc only selects ARCH_HAS_STRICT_MODULE_RWX when 
ARCH_HAS_STRICT_KERNEL_RWX is also selected.

I think it will work. It's slightly rude to select things like that, but
I think it's OK for something like this.

Medium term we can possibly just have the generic STRICT_MODULE_RWX
depend on STRICT_KERNEL_RWX.

cheers