Re: [PATCH] x86/its: Make ITS thunk pages read-only without the ROX execmem cache

[Dave Hansen <dave.hansen@intel.com>]

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On 10/1/26 06:22, Frédéric MARIE-JOSEPH wrote:
> That's my first post so I hope I do things right. I found what seems to
> me like a bug, and worked with Claude to find a patch. Hope it will be
> usefull.

Your mailer is sending out HTML, but there was a plain-text version too,
so the message at least made it to the archives. Using git-send-email is
the most foolproof way to send these things, fwiw.

> With CONFIG_MODULES=n there is no STRICT_MODULE_RWX, so x86 does not
> select ARCH_HAS_EXECMEM_ROX and execmem_restore_rox() is the stub that
> returns 0.

Ugh. The origin of this seems to be:

         select ARCH_HAS_EXECMEM_ROX             if X86_64 &&
STRICT_MODULE_RWX
from:

> commit 47410d839fcda6890cb82828f874f97710982f24
> Author: Mike Rapoport (Microsoft) <rppt@kernel.org>
> Date:   Tue Jun 3 14:14:42 2025 +0300
> 
>     x86/Kconfig: only enable ROX cache in execmem when STRICT_MODULE_RWX is set

That commit is trying to change execmem internal details via an
arch-specific Kconfig tweak. It's also logically a bit silly that what
an arch supports:

	ARCH_HAS_EXECMEM_ROX

depends on a module-specific option:

	STRICT_MODULE_RWX

If execmem is being too aggressive on for modules on !STRICT_MODULE_RWX
configs, shouldn't the fix be in execmem *module* code?

Maybe something along the line of the lightly-tested attached patch? I
see the "11 W+X pages found" message without it, and the message goes
away when it is applied.

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---

 b/arch/x86/Kconfig     |    2 +-
 b/kernel/module/main.c |    3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff -puN arch/x86/Kconfig~x86-STRICT_MODULE_RWX arch/x86/Kconfig
--- a/arch/x86/Kconfig~x86-STRICT_MODULE_RWX	2026-10-01 06:31:14.379577124 -0700
+++ b/arch/x86/Kconfig	2026-10-01 06:31:39.777436090 -0700
@@ -85,7 +85,7 @@ config X86
 	select ARCH_HAS_DMA_OPS			if GART_IOMMU || XEN
 	select ARCH_HAS_EARLY_DEBUG		if KGDB
 	select ARCH_HAS_ELF_RANDOMIZE
-	select ARCH_HAS_EXECMEM_ROX		if X86_64 && STRICT_MODULE_RWX
+	select ARCH_HAS_EXECMEM_ROX		if X86_64
 	select ARCH_HAS_FAST_MULTIPLIER
 	select ARCH_HAS_FORTIFY_SOURCE
 	select ARCH_HAS_GCOV_PROFILE_ALL
diff -puN kernel/module/main.c~x86-STRICT_MODULE_RWX kernel/module/main.c
--- a/kernel/module/main.c~x86-STRICT_MODULE_RWX	2026-10-01 06:44:42.417795788 -0700
+++ b/kernel/module/main.c	2026-10-01 06:51:28.048722976 -0700
@@ -1355,7 +1355,8 @@ static int module_memory_alloc(struct mo
 	if (!ptr)
 		return -ENOMEM;
 
-	mod->mem[type].is_rox = execmem_is_rox(execmem_type);
+	if (IS_ENABLED(STRICT_MODULE_RWX))
+		mod->mem[type].is_rox = execmem_is_rox(execmem_type);
 
 	/*
 	 * The pointer to these blocks of memory are stored on the module
_