[tip: x86/mm] x86/mm/pat: Use pr_warn() for early W^X warnings

[tip-bot2 for Mike Rapoport (Microsoft)]

The following commit has been merged into the x86/mm branch of tip:

Commit-ID:     ea6fd393cb9e6811a748c7551de0dd3090f9dcde
Gitweb:        https://git.kernel.org/tip/ea6fd393cb9e6811a748c7551de0dd3090f9dcde
Author:        Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
AuthorDate:    Sun, 13 Sep 2026 10:37:27 +03:00
Committer:     Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CommitterDate: Mon, 21 Sep 2026 12:23:22 -07:00

x86/mm/pat: Use pr_warn() for early W^X warnings

Nathan Chancellor reports the following warning:

  CPA detected W^X violation: 8000000000000123 -> 0000000000000123 range: 0xffffffffc0400000 - 0xffffffffc0400fff PFN 100e00

from its_alloc() doing set_memory_x() during early retpoline setup.

The warning is not factually wrong but it is unproductive. First, the RWX
permission is temporary and fixed up by execmem_restore_rox(). Second,
at the time of the warning, all kernel text is mapped RWX. So there is not
even a transient actual security issue.

The right way to fix this up is to relax RWX detection during boot but
make a final verification pass over all kernel page tables before running
userspace.  There is code to do that today (debug_checkwx()) but it
must be enabled explicitly in Kconfig.

For now, retain the warning even if it's unproductive, but make it
scream less loudly: use pr_warn_once() rather than WARN_ONCE().

Remove the warning once debug_checkwx() behavior becomes unconditional.

Closes: https://lore.kernel.org/all/20260905044253.GA3816371@ax162
Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Tested-by: Ihor Solodrai <ihor.solodrai@xxxxxxxxx>
Link: https://patch.msgid.link/20260913-fixes-verify-rwx-v3-1-5e1d6a08bd02@xxxxxxxxxx
---
 arch/x86/mm/pat/set_memory.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index b306000..a799f53 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -697,6 +697,21 @@ static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long star
 		return new;
 
 	end = start + npg * PAGE_SIZE - 1;
+
+	/*
+	 * If the kernel text is still RWX, gently complain, this could be a
+	 * false positive.
+	 * Once debug_checkwx() becomes mandatory for CONFIG_STRICT_KERNEL_RWX,
+	 * the warning can be removed completely.
+	 */
+	if (!kernel_set_to_readonly) {
+		pr_warn_once("CPA detected W^X violation: %016llx -> %016llx range: 0x%016lx - 0x%016lx PFN %lx\n",
+		  (unsigned long long)pgprot_val(old),
+		  (unsigned long long)pgprot_val(new),
+		  start, end, pfn);
+		return new;
+	}
+
 	WARN_ONCE(1, "CPA detected W^X violation: %016llx -> %016llx range: 0x%016lx - 0x%016lx PFN %lx\n",
 		  (unsigned long long)pgprot_val(old),
 		  (unsigned long long)pgprot_val(new),