[RFC PATCH v1 13/28] riscv mmu: teach pte_mkwrite to manufacture shadow stack PTEs

[debug at rivosinc.com]

From: Deepak Gupta <debug at 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.

On riscv, presence of only VM_WRITE in vma->vm_flags means it's a shadow stack.

Signed-off-by: Deepak Gupta <debug at rivosinc.com>

rebase with a30f0ca0fa31cdb2ac3d24b7b5be9e3ae75f4175

Implementation of pte_mkwrite and pmd_mkwrite on riscv

Signed-off-by: Deepak Gupta <debug at rivosinc.com>
---
 arch/riscv/include/asm/pgtable.h |  7 +++++++
 arch/riscv/mm/pgtable.c          | 21 +++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 7ed00b4cc73d..9477108e727d 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -403,6 +403,10 @@ 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);
@@ -706,6 +710,9 @@ 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 fef4e7328e49..9b1845f93ea1 100644
--- a/arch/riscv/mm/pgtable.c
+++ b/arch/riscv/mm/pgtable.c
@@ -101,3 +101,24 @@ 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 (arch_is_shadow_stack(vma->vm_flags))
+		return pte_mkwrite_shstk(pte);
+
+	pte = pte_mkwrite_novma(pte);
+
+	return pte;
+}
+
+pmd_t pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
+{
+	if (arch_is_shadow_stack(vma->vm_flags))
+		return pmd_mkwrite_shstk(pmd);
+
+	pmd = pmd_mkwrite_novma(pmd);
+
+	return pmd;
+}
+
-- 
2.43.0