[PATCH v2 3/3] arm64/mm: Add uffd write-protect support

Ryan Roberts
2024-04-29T14:02:24Z

Let's use the newly-free PTE SW bit (58) to add support for uffd-wp.

The standard handlers are implemented for set/test/clear for both pte
and pmd. Additionally we must also track the uffd-wp state as a pte swp
bit, so use a free swap pte bit (3).

Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/pgtable-prot.h | 8 +++++
arch/arm64/include/asm/pgtable.h | 44 +++++++++++++++++++++++++++
3 files changed, 53 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7b11c98b3e84..763e221f2169 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -255,6 +255,7 @@ config ARM64
select SYSCTL_EXCEPTION_TRACE
select THREAD_INFO_IN_TASK
select HAVE_ARCH_USERFAULTFD_MINOR if USERFAULTFD
+ select HAVE_ARCH_USERFAULTFD_WP if USERFAULTFD
select TRACE_IRQFLAGS_SUPPORT
select TRACE_IRQFLAGS_NMI_SUPPORT
select HAVE_SOFTIRQ_ON_OWN_STACK
diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
index ddf55895c9c2..a5e7dd37bb0a 100644
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -20,6 +20,14 @@
#define PTE_DEVMAP (_AT(pteval_t, 1) << 57)
#define PTE_INVALID (PTE_NS) /* only when !PTE_VALID */

+#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP
+#define PTE_UFFD_WP (_AT(pteval_t, 1) << 58) /* uffd-wp tracking */
+#define PTE_SWP_UFFD_WP (_AT(pteval_t, 1) << 3) /* only for swp ptes */
+#else
+#define PTE_UFFD_WP (_AT(pteval_t, 0))
+#define PTE_SWP_UFFD_WP (_AT(pteval_t, 0))
+#endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */
+
#define _PROT_DEFAULT (PTE_TYPE_PAGE | PTE_AF | PTE_SHARED)
#define _PROT_SECT_DEFAULT (PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index d966d2ee1097..759ba8c32a58 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -279,6 +279,23 @@ static inline pte_t pte_mkdevmap(pte_t pte)
return set_pte_bit(pte, __pgprot(PTE_DEVMAP | PTE_SPECIAL));
}

+#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP
+static inline int pte_uffd_wp(pte_t pte)
+{
+ return !!(pte_val(pte) & PTE_UFFD_WP);
+}
+
+static inline pte_t pte_mkuffd_wp(pte_t pte)
+{
+ return pte_wrprotect(set_pte_bit(pte, __pgprot(PTE_UFFD_WP)));
+}
+
+static inline pte_t pte_clear_uffd_wp(pte_t pte)
+{
+ return clear_pte_bit(pte, __pgprot(PTE_UFFD_WP));
+}
+#endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */
+
static inline void __set_pte(pte_t *ptep, pte_t pte)
{
WRITE_ONCE(*ptep, pte);
@@ -471,6 +488,23 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
return clear_pte_bit(pte, __pgprot(PTE_SWP_EXCLUSIVE));
}

+#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP
+static inline pte_t pte_swp_mkuffd_wp(pte_t pte)
+{
+ return set_pte_bit(pte, __pgprot(PTE_SWP_UFFD_WP));
+}
+
+static inline int pte_swp_uffd_wp(pte_t pte)
+{
+ return !!(pte_val(pte) & PTE_SWP_UFFD_WP);
+}
+
+static inline pte_t pte_swp_clear_uffd_wp(pte_t pte)
+{
+ return clear_pte_bit(pte, __pgprot(PTE_SWP_UFFD_WP));
+}
+#endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */
+
#ifdef CONFIG_NUMA_BALANCING
/*
* See the comment in include/linux/pgtable.h
@@ -512,6 +546,15 @@ static inline int pmd_trans_huge(pmd_t pmd)
#define pmd_mkdirty(pmd) pte_pmd(pte_mkdirty(pmd_pte(pmd)))
#define pmd_mkyoung(pmd) pte_pmd(pte_mkyoung(pmd_pte(pmd)))
#define pmd_mkinvalid(pmd) pte_pmd(pte_mkinvalid(pmd_pte(pmd)))
+#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP
+#define pmd_uffd_wp(pmd) pte_uffd_wp(pmd_pte(pmd))
+#define pmd_mkuffd_wp(pmd) pte_pmd(pte_mkuffd_wp(pmd_pte(pmd)))
+#define pmd_clear_uffd_wp(pmd) pte_pmd(pte_clear_uffd_wp(pmd_pte(pmd)))
+#define pmd_swp_uffd_wp(pmd) pte_swp_uffd_wp(pmd_pte(pmd))
+#define pmd_swp_mkuffd_wp(pmd) pte_pmd(pte_swp_mkuffd_wp(pmd_pte(pmd)))
+#define pmd_swp_clear_uffd_wp(pmd) \
+ pte_pmd(pte_swp_clear_uffd_wp(pmd_pte(pmd)))
+#endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */

#define pmd_thp_or_huge(pmd) (pmd_huge(pmd) || pmd_trans_huge(pmd))

@@ -1244,6 +1287,7 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma,
* Encode and decode a swap entry:
* bits 0-1: present (must be zero)
* bits 2: remember PG_anon_exclusive
+ * bit 3: remember uffd-wp state
* bit 5: PTE_INVALID (must be zero)
* bits 6-10: swap type
* bits 11-60: swap offset
--
2.25.1