[PATCH v10 14/26] x86/mm: Update maybe_mkwrite() for shadow stack

[Yu-cheng Yu]

Shadow stack memory is writable, but its VMA has VM_SHSTK instead of
VM_WRITE.  Update maybe_mkwrite() to include the shadow stack.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
---
 arch/x86/Kconfig              |  4 ++++
 arch/x86/mm/pgtable.c         | 18 ++++++++++++++++++
 include/asm-generic/pgtable.h | 24 ++++++++++++++++++++++++
 include/linux/mm.h            |  2 ++
 mm/huge_memory.c              |  2 ++
 5 files changed, 50 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index c98f82fffe85..ac07e1f6a2bc 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1955,6 +1955,9 @@ config AS_HAS_SHADOW_STACK
 config X86_INTEL_CET
 	def_bool n
 
+config ARCH_MAYBE_MKWRITE
+	def_bool n
+
 config ARCH_HAS_SHADOW_STACK
 	def_bool n
 
@@ -1965,6 +1968,7 @@ config X86_INTEL_SHADOW_STACK_USER
 	depends on AS_HAS_SHADOW_STACK
 	select ARCH_USES_HIGH_VMA_FLAGS
 	select X86_INTEL_CET
+	select ARCH_MAYBE_MKWRITE
 	select ARCH_HAS_SHADOW_STACK
 	help
 	  Shadow Stacks provides protection against program stack
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 7bd2c3a52297..aa4d396ff98d 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -603,6 +603,24 @@ int pmdp_clear_flush_young(struct vm_area_struct *vma,
 }
 #endif
 
+#ifdef CONFIG_ARCH_MAYBE_MKWRITE
+pte_t arch_maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
+{
+	if (likely(vma->vm_flags & VM_SHSTK))
+		pte = pte_mkwrite_shstk(pte);
+	return pte;
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+pmd_t arch_maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
+{
+	if (likely(vma->vm_flags & VM_SHSTK))
+		pmd = pmd_mkwrite_shstk(pmd);
+	return pmd;
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+#endif /* CONFIG_ARCH_MAYBE_MKWRITE */
+
 /**
  * reserve_top_address - reserves a hole in the top of kernel address space
  * @reserve - size of hole to reserve
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 329b8c8ca703..2c3875724809 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -1191,6 +1191,30 @@ static inline bool arch_has_pfn_modify_check(void)
 }
 #endif /* !_HAVE_ARCH_PFN_MODIFY_ALLOWED */
 
+#ifdef CONFIG_MMU
+#ifdef CONFIG_ARCH_MAYBE_MKWRITE
+pte_t arch_maybe_mkwrite(pte_t pte, struct vm_area_struct *vma);
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+pmd_t arch_maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma);
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
+#else /* !CONFIG_ARCH_MAYBE_MKWRITE */
+static inline pte_t arch_maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
+{
+	return pte;
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline pmd_t arch_maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
+{
+	return pmd;
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
+#endif /* CONFIG_ARCH_MAYBE_MKWRITE */
+#endif /* CONFIG_MMU */
+
 /*
  * Architecture PAGE_KERNEL_* fallbacks
  *
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 54bb4cd9fee8..f0669e3cdd37 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -944,6 +944,8 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
 {
 	if (likely(vma->vm_flags & VM_WRITE))
 		pte = pte_mkwrite(pte);
+	else
+		pte = arch_maybe_mkwrite(pte, vma);
 	return pte;
 }
 
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 6ecd1045113b..608746bb9d19 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -485,6 +485,8 @@ pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
 {
 	if (likely(vma->vm_flags & VM_WRITE))
 		pmd = pmd_mkwrite(pmd);
+	else
+		pmd = arch_maybe_pmd_mkwrite(pmd, vma);
 	return pmd;
 }
 
-- 
2.21.0