[RFC][PATCH] x86/mm: Disconnect RWX module checking from execmem

[Dave Hansen]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

Frédéric reported:

	x86/mm: Checked W+X mappings: FAILED, 7 W+X pages found.

errors on a build with modules disabled. There are some build
dependencies in play:

 * ARCH_HAS_EXECMEM_ROX depends on STRICT_MODULE_RWX
 * STRICT_MODULE_RWX depends on MODULES
 * execmem_restore_rox() is a stub without ARCH_HAS_EXECMEM_ROX=y

execmem_restore_rox() is what the x86 "ITS" code uses to zap its
W+X mappings during early boot. The error message comes from
CONFIG_DEBUG_WX which is independent from any of the other options.

But the nutty part is that there is any connection at all between
ARCH_HAS_EXECMEM_ROX and STRICT_MODULE_RWX.

Restore a functional execmem_restore_rox() to all 64-bit builds by
eliminating the STRICT_MODULE_RWX dependency.

Then, turn our attention to execmem. 47410d839fcd "x86/Kconfig: only
enable ROX cache...") was trying to make module memory access more
permissive unless STRICT_MODULE_RWX is in play. For execmem, never
consider module memory to be ROX except under STRICT_MODULE_RWX.

This seems to fix Frédéric's issue, but I'm a bit worried that it
has other implications in the execmem code. For instance, the
module_enable_text_rox() loop is now rather weird mem->is_rox is
now directly dependent on STRICT_MODULE_RWX.

Mike, do you see anything bad happening on the execmem side if we
do this?

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Tested-by: Frederic MARIE-JOSEPH <fredericmariejoseph@xxxxxxxxx>
Reported-by: Frederic MARIE-JOSEPH <fredericmariejoseph@xxxxxxxxx>
Link: https://lore.kernel.org/all/20261001-x86-fault-spurious-rw-v1-1-7fe1189b5efd@xxxxxxxxxxx/
Fixes: a82b26451de1 ("x86/its: explicitly manage permissions for ITS pages")
Cc: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Cc: Petr Pavlu <petr.pavlu@xxxxxxxx>
Cc: Daniel Gomez <da.gomez@xxxxxxxxxx>
Cc: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
Cc: Aaron Tomlin <atomlin@xxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-modules@xxxxxxxxxxxxxxx
---

 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 07:11:50.443595828 -0700
+++ b/arch/x86/Kconfig	2026-10-01 07:11:50.454595751 -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 07:11:50.449595786 -0700
+++ b/kernel/module/main.c	2026-10-01 09:47:20.842360625 -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(CONFIG_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
_