[RFC PATCH 10/16] mm: Map page tables with privileged pkey

[Kevin Brodsky]

If CONFIG_KPKEYS_HARDENED_PGTABLES is enabled, map allocated page
table pages using a privileged pkey (KPKEYS_PKEY_PGTABLES), so that
page tables can only be written under guard(kpkeys_hardened_pgtables).

This patch is a no-op if CONFIG_KPKEYS_HARDENED_PGTABLES is disabled
(default).

Signed-off-by: Kevin Brodsky <kevin.brodsky@xxxxxxx>
---
 include/linux/mm.h | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 683e883dae77..4fb25454ba85 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -31,6 +31,7 @@
 #include <linux/kasan.h>
 #include <linux/memremap.h>
 #include <linux/slab.h>
+#include <linux/kpkeys.h>
 
 struct mempolicy;
 struct anon_vma;
@@ -2895,7 +2896,19 @@ static inline bool pagetable_is_reserved(struct ptdesc *pt)
  */
 static inline struct ptdesc *pagetable_alloc_noprof(gfp_t gfp, unsigned int order)
 {
-	struct page *page = alloc_pages_noprof(gfp | __GFP_COMP, order);
+	struct page *page;
+	int ret;
+
+	page = alloc_pages_noprof(gfp | __GFP_COMP, order);
+	if (!page)
+		return NULL;
+
+	ret = kpkeys_protect_pgtable_memory((unsigned long)page_address(page),
+					    1 << order);
+	if (ret) {
+		__free_pages(page, order);
+		return NULL;
+	}
 
 	return page_ptdesc(page);
 }
@@ -2911,8 +2924,11 @@ static inline struct ptdesc *pagetable_alloc_noprof(gfp_t gfp, unsigned int orde
 static inline void pagetable_free(struct ptdesc *pt)
 {
 	struct page *page = ptdesc_page(pt);
+	unsigned int order = compound_order(page);
 
-	__free_pages(page, compound_order(page));
+	kpkeys_unprotect_pgtable_memory((unsigned long)page_address(page),
+					1 << order);
+	__free_pages(page, order);
 }
 
 #if defined(CONFIG_SPLIT_PTE_PTLOCKS)
-- 
2.47.0