[PATCH v4 13/30] riscv mmu: teach pte_mkwrite to manufacture shadow stack PTEs

[Deepak Gupta <debug@rivosinc.com>]

pte_mkwrite creates PTEs with WRITE encodings for underlying arch.
Underlying arch can have two types of writeable mappings. One that can be
written using regular store instructions. Another one that can only be
written using specialized store instructions (like shadow stack stores).
pte_mkwrite can select write PTE encoding based on VMA range (i.e.
VM_SHADOW_STACK)

Signed-off-by: Deepak Gupta <debug@rivosinc.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
 arch/riscv/include/asm/pgtable.h |  7 +++++++
 arch/riscv/mm/pgtable.c          | 17 +++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 0b6c66fb853a..30fd4874e871 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -420,6 +420,10 @@ static inline pte_t pte_wrprotect(pte_t pte)
 
 /* static inline pte_t pte_mkread(pte_t pte) */
 
+struct vm_area_struct;
+pte_t pte_mkwrite(pte_t pte, struct vm_area_struct *vma);
+#define pte_mkwrite pte_mkwrite
+
 static inline pte_t pte_mkwrite_novma(pte_t pte)
 {
 	return __pte(pte_val(pte) | _PAGE_WRITE);
@@ -732,6 +736,9 @@ static inline pmd_t pmd_mkyoung(pmd_t pmd)
 	return pte_pmd(pte_mkyoung(pmd_pte(pmd)));
 }
 
+pmd_t pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma);
+#define pmd_mkwrite pmd_mkwrite
+
 static inline pmd_t pmd_mkwrite_novma(pmd_t pmd)
 {
 	return pte_pmd(pte_mkwrite_novma(pmd_pte(pmd)));
diff --git a/arch/riscv/mm/pgtable.c b/arch/riscv/mm/pgtable.c
index 533ec9055fa0..0dd6104a35ac 100644
--- a/arch/riscv/mm/pgtable.c
+++ b/arch/riscv/mm/pgtable.c
@@ -142,3 +142,20 @@ pmd_t pmdp_collapse_flush(struct vm_area_struct *vma,
 	return pmd;
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
+pte_t pte_mkwrite(pte_t pte, struct vm_area_struct *vma)
+{
+	if (vma->vm_flags & VM_SHADOW_STACK)
+		return pte_mkwrite_shstk(pte);
+
+	return pte_mkwrite_novma(pte);
+}
+
+pmd_t pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
+{
+	if (vma->vm_flags & VM_SHADOW_STACK)
+		return pmd_mkwrite_shstk(pmd);
+
+	return pmd_mkwrite_novma(pmd);
+}
+
-- 
2.45.0