[PATCH v2] x86/mm/pat: fix effective RW computation in lookup_address_in_pgd_attr()

[Mike Rapoport (Microsoft)]

lookup_address_in_pgd_attr() accumulates the effective NX and RW bits of
the walked page table levels so that verify_rwx() can detect mappings that
are both writable and executable.

The RW bits are folded into a bool with

	rw &= pXd_flags(*pXd) & _PAGE_RW;

but _PAGE_RW is 0x2. So consider the accumulation line:

        rw &= pXd_flags(*pXd) & _PAGE_RW;

where rw=0x1 and the right side evaluates down to 0x2. It'll end up doing:

        rw = 0x1 & 0x2

and rw always ends up 0.

This way rw becomes false at the first level walked, regardless of the
actual permissions, and verify_rwx() treats every mapping as non-writable
and never reports a W^X violation.

Add double negation to the right side to normalize the _PAGE_RW flag to
0 or 1.

Fixes: ceb647b4b529 ("x86/pat: Introduce lookup_address_in_pgd_attr()")
Assisted-by: Copilot:claude-opus-4.8
Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
---
v2 changes:
* use a simpler version that uses !! to ensure the comparison result is
  0 or 1

v1: https://patch.msgid.link/20260716-verify-rwx-fix-v1-1-d8a04854df06@xxxxxxxxxx
---
 arch/x86/mm/pat/set_memory.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index d023a40a1e03..cd9ecc8e52f9 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -731,7 +731,7 @@ pte_t *lookup_address_in_pgd_attr(pgd_t *pgd, unsigned long address,
 
 	*level = PG_LEVEL_512G;
 	*nx |= pgd_flags(*pgd) & _PAGE_NX;
-	*rw &= pgd_flags(*pgd) & _PAGE_RW;
+	*rw &= !!(pgd_flags(*pgd) & _PAGE_RW);
 
 	p4d = p4d_offset(pgd, address);
 	if (p4d_none(*p4d))
@@ -742,7 +742,7 @@ pte_t *lookup_address_in_pgd_attr(pgd_t *pgd, unsigned long address,
 
 	*level = PG_LEVEL_1G;
 	*nx |= p4d_flags(*p4d) & _PAGE_NX;
-	*rw &= p4d_flags(*p4d) & _PAGE_RW;
+	*rw &= !!(p4d_flags(*p4d) & _PAGE_RW);
 
 	pud = pud_offset(p4d, address);
 	if (pud_none(*pud))
@@ -753,7 +753,7 @@ pte_t *lookup_address_in_pgd_attr(pgd_t *pgd, unsigned long address,
 
 	*level = PG_LEVEL_2M;
 	*nx |= pud_flags(*pud) & _PAGE_NX;
-	*rw &= pud_flags(*pud) & _PAGE_RW;
+	*rw &= !!(pud_flags(*pud) & _PAGE_RW);
 
 	pmd = pmd_offset(pud, address);
 	if (pmd_none(*pmd))
@@ -764,7 +764,7 @@ pte_t *lookup_address_in_pgd_attr(pgd_t *pgd, unsigned long address,
 
 	*level = PG_LEVEL_4K;
 	*nx |= pmd_flags(*pmd) & _PAGE_NX;
-	*rw &= pmd_flags(*pmd) & _PAGE_RW;
+	*rw &= !!(pmd_flags(*pmd) & _PAGE_RW);
 
 	return pte_offset_kernel(pmd, address);
 }

---
base-commit: a13c140cc289c0b7b3770bce5b3ad42ab35074aa
change-id: 20260716-verify-rwx-fix-3b0bd3e51244

--
Sincerely yours,
Mike.