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

From: Dave Hansen <dave.hansen@linux.intel.com>

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@linux.intel.com>
Tested-by: Frederic MARIE-JOSEPH <redacted>
Reported-by: Frederic MARIE-JOSEPH <redacted>
Link: https://lore.kernel.org/all/20261001-x86-fault-spurious-rw-v1-1-7fe1189b5efd@imperva.com/ (local)
Fixes: a82b26451de1 ("x86/its: explicitly manage permissions for ITS pages")
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Petr Pavlu <petr.pavlu@suse.com>
Cc: Daniel Gomez <da.gomez@kernel.org>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Aaron Tomlin <atomlin@atomlin.com>
Cc: <redacted>
Cc: <redacted>
---

 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

_