[PATCH RFC v3 19/21] mm/pgtable: disallow calling (pgd|p4d|pud)_page, pgd_page_vaddr() and (p4d|pud)_pgtable with dummy

[Yeoreum Yun]

From: "David Hildenbrand (Arm)" <david at kernel.org>

These helpers silently fallback to the folded helpers. With e.g., pdgp_get()
returning dummy values, pgd_page_vaddr(pgdp_get(pgdp)) will now behave
differently than pgd_page_vaddr(*pgdp).

Disallow calling (pgd|p4d|pud)_page() entirely, and catch when passing a
dummy value to pgd_page_vaddr() and (p4d|pud)_pgtable.
This will catch most abuse of dummy pXdp value at compile time --
so far there were none, and it better stay that way.

Signed-off-by: David Hildenbrand (Arm) <david at kernel.org>
Co-developed-by: Yeoreum Yun <yeoreum.yun at arm.com>
Signed-off-by: Yeoreum Yun <yeoreum.yun at arm.com>
---
 include/asm-generic/pgtable-nop4d.h | 8 ++++++--
 include/asm-generic/pgtable-nopmd.h | 8 ++++++--
 include/asm-generic/pgtable-nopud.h | 8 ++++++--
 3 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/include/asm-generic/pgtable-nop4d.h b/include/asm-generic/pgtable-nop4d.h
index 2d86325235da..d2dccf7542da 100644
--- a/include/asm-generic/pgtable-nop4d.h
+++ b/include/asm-generic/pgtable-nop4d.h
@@ -70,8 +70,12 @@ static __always_inline p4d_t *__p4d_offset_lockless(pgd_t *pgdp, pgd_t pgd,
 #define p4d_val(x)				(pgd_val((x).pgd))
 #define __p4d(x)				((p4d_t) { __pgd(x) })
 
-#define pgd_page(pgd)				(p4d_page((p4d_t){ pgd }))
-#define pgd_page_vaddr(pgd)			((unsigned long)(p4d_pgtable((p4d_t){ pgd })))
+#define pgd_page(pgd)				({ BUILD_BUG(); (struct page *)NULL; })
+#define pgd_page_vaddr(pgd)						\
+({ 									\
+	pgd_check_dummy(pgd);						\
+	(unsigned long)p4d_pgtable((p4d_t) { pgd });			\
+})
 
 /*
  * allocating and freeing a p4d is trivial: the 1-entry p4d is
diff --git a/include/asm-generic/pgtable-nopmd.h b/include/asm-generic/pgtable-nopmd.h
index bd40d3a5743f..2afbf2d8659d 100644
--- a/include/asm-generic/pgtable-nopmd.h
+++ b/include/asm-generic/pgtable-nopmd.h
@@ -79,8 +79,12 @@ static __always_inline pmd_t *__pmd_offset_lockless(pud_t *pudp, pud_t pud,
 #define pmd_val(x)				(pud_val((x).pud))
 #define __pmd(x)				((pmd_t) { __pud(x) } )
 
-#define pud_page(pud)				(pmd_page((pmd_t){ pud }))
-#define pud_pgtable(pud)			((pmd_t *)(pmd_page_vaddr((pmd_t){ pud })))
+#define pud_page(pud)				({ BUILD_BUG(); (struct page *)NULL; })
+#define pud_pgtable(pud)						\
+({									\
+	pud_check_dummy(pud);						\
+	((pmd_t *)(pmd_page_vaddr((pmd_t) { pud })));			\
+})
 
 /*
  * allocating and freeing a pmd is trivial: the 1-entry pmd is
diff --git a/include/asm-generic/pgtable-nopud.h b/include/asm-generic/pgtable-nopud.h
index 7475d0bd0f2e..3264673c0c38 100644
--- a/include/asm-generic/pgtable-nopud.h
+++ b/include/asm-generic/pgtable-nopud.h
@@ -77,8 +77,12 @@ static __always_inline pud_t *__pud_offset_lockless(p4d_t *p4dp, p4d_t p4d,
 #define pud_val(x)				(p4d_val((x).p4d))
 #define __pud(x)				((pud_t) { __p4d(x) })
 
-#define p4d_page(p4d)				(pud_page((pud_t){ p4d }))
-#define p4d_pgtable(p4d)			((pud_t *)(pud_pgtable((pud_t){ p4d })))
+#define p4d_page(p4d)				({ BUILD_BUG(); (struct page *)NULL; })
+#define p4d_pgtable(p4d)						\
+({									\
+	p4d_check_dummy(p4d);						\
+	((pud_t *)(pud_pgtable((pud_t) { p4d })));			\
+})
 
 /*
  * allocating and freeing a pud is trivial: the 1-entry pud is

-- 
2.43.0