[PATCH 6.6.y 1/3] mm: userfaultfd: add pgtable_supports_uffd_wp()

From: Chunyan Zhang <[email protected]>

[ Upstream commit f59c0924d61aa2a2bb85936a593140f327112787 ]

Some platforms can customize the PTE/PMD entry uffd-wp bit making it
unavailable even if the architecture provides the resource.  This patch
adds a macro API pgtable_supports_uffd_wp() that allows architectures to
define their specific implementations to check if the uffd-wp bit is
available on which device the kernel is running.

Also this patch is removing "ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP" and
"ifdef CONFIG_PTE_MARKER_UFFD_WP" in favor of pgtable_supports_uffd_wp()
and uffd_supports_wp_marker() checks respectively that default to
IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP) and
"IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP) &&
IS_ENABLED(CONFIG_PTE_MARKER_UFFD_WP)" if not overridden by the
architecture, no change in behavior is expected.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Chunyan Zhang <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: Albert Ou <[email protected]>
Cc: Alexandre Ghiti <[email protected]>
Cc: Alexandre Ghiti <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Andrew Jones <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Axel Rasmussen <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Conor Dooley <[email protected]>
Cc: Conor Dooley <[email protected]>
Cc: Deepak Gupta <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Liam Howlett <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
Cc: Paul Walmsley <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Rob Herring <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Yuanchu Xie <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Stable-dep-of: 3c58f641e813 ("userfaultfd: prevent registration of special VMAs")
Signed-off-by: Sasha Levin <[email protected]>
---
 fs/userfaultfd.c                   | 20 ++++++++++----------
 include/asm-generic/pgtable_uffd.h | 17 +++++++++++++++++
 include/linux/mm_inline.h          |  7 ++++---
 include/linux/userfaultfd_k.h      |  8 +++++---
 4 files changed, 36 insertions(+), 16 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 49f0742625981..0ebdf3c2c9ee6 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1354,9 +1354,9 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
 		vm_flags |= VM_UFFD_MISSING;
 	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
-#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
-		goto out;
-#endif
+		if (!pgtable_supports_uffd_wp())
+			goto out;
+
 		vm_flags |= VM_UFFD_WP;
 	}
 	if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
@@ -2068,13 +2068,13 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
 	uffdio_api.features &=
 		~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
 #endif
-#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
-	uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
-#endif
-#ifndef CONFIG_PTE_MARKER_UFFD_WP
-	uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
-	uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED;
-#endif
+	if (!pgtable_supports_uffd_wp())
+		uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
+
+	if (!uffd_supports_wp_marker()) {
+		uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
+		uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED;
+	}
 
 	ret = -EINVAL;
 	if (features & ~uffdio_api.features)
diff --git a/include/asm-generic/pgtable_uffd.h b/include/asm-generic/pgtable_uffd.h
index 828966d4c2811..0d85791efdf77 100644
--- a/include/asm-generic/pgtable_uffd.h
+++ b/include/asm-generic/pgtable_uffd.h
@@ -1,6 +1,23 @@
 #ifndef _ASM_GENERIC_PGTABLE_UFFD_H
 #define _ASM_GENERIC_PGTABLE_UFFD_H
 
+/*
+ * Some platforms can customize the uffd-wp bit, making it unavailable
+ * even if the architecture provides the resource.
+ * Adding this API allows architectures to add their own checks for the
+ * devices on which the kernel is running.
+ * Note: When overriding it, please make sure the
+ * CONFIG_HAVE_ARCH_USERFAULTFD_WP is part of this macro.
+ */
+#ifndef pgtable_supports_uffd_wp
+#define pgtable_supports_uffd_wp()	IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP)
+#endif
+
+static inline bool uffd_supports_wp_marker(void)
+{
+	return pgtable_supports_uffd_wp() && IS_ENABLED(CONFIG_PTE_MARKER_UFFD_WP);
+}
+
 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
 static __always_inline int pte_uffd_wp(pte_t pte)
 {
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index 96b1c157554c0..4fbf25c45ec91 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -547,7 +547,6 @@ static inline pte_marker copy_pte_marker(
 
 	return dstm;
 }
-#endif
 
 /*
  * If this pte is wr-protected by uffd-wp in any form, arm the special pte to
@@ -565,9 +564,11 @@ static inline void
 pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long addr,
 			      pte_t *pte, pte_t pteval)
 {
-#ifdef CONFIG_PTE_MARKER_UFFD_WP
 	bool arm_uffd_pte = false;
 
+	if (!uffd_supports_wp_marker())
+		return;
+
 	/* The current status of the pte should be "cleared" before calling */
 	WARN_ON_ONCE(!pte_none(ptep_get(pte)));
 
@@ -594,7 +595,6 @@ pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long addr,
 	if (unlikely(arm_uffd_pte))
 		set_pte_at(vma->vm_mm, addr, pte,
 			   make_pte_marker(PTE_MARKER_UFFD_WP));
-#endif
 }
 
 static inline bool vma_has_recency(struct vm_area_struct *vma)
@@ -607,5 +607,6 @@ static inline bool vma_has_recency(struct vm_area_struct *vma)
 
 	return true;
 }
+#endif
 
 #endif
diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index ac8c6854097cd..fac0f3d0deb9a 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -166,15 +166,17 @@ static inline bool vma_can_userfault(struct vm_area_struct *vma,
 	if ((vm_flags & VM_UFFD_MINOR) &&
 	    (!is_vm_hugetlb_page(vma) && !vma_is_shmem(vma)))
 		return false;
-#ifndef CONFIG_PTE_MARKER_UFFD_WP
+
 	/*
 	 * If user requested uffd-wp but not enabled pte markers for
 	 * uffd-wp, then shmem & hugetlbfs are not supported but only
 	 * anonymous.
 	 */
-	if ((vm_flags & VM_UFFD_WP) && !vma_is_anonymous(vma))
+	if (!uffd_supports_wp_marker() && (vm_flags & VM_UFFD_WP) &&
+	    !vma_is_anonymous(vma))
 		return false;
-#endif
+
+	/* By default, allow any of anon|shmem|hugetlb */
 	return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
 	    vma_is_shmem(vma);
 }
-- 
2.53.0