[PATCH v26 08/28] riscv/mm: teach pte_mkwrite to manufacture shadow stack PTEs

Deepak Gupta via B4 Relay
2025-12-11T17:21:07Z

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)

Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Zong Li <zong.li@sifive.com>
Tested-by: Andreas Korb <andreas.korb@aisec.fraunhofer.de>
Tested-by: Valentin Haudiquet <valentin.haudiquet@canonical.com>
Signed-off-by: Deepak Gupta <debug@rivosinc.com>
---
arch/riscv/include/asm/pgtable.h | 7 +++++++
arch/riscv/mm/pgtable.c | 16 ++++++++++++++++
2 files changed, 23 insertions(+)

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index e4eb4657e1b6..b03e8f85221f 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);
@@ -765,6 +769,9 @@ 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 8b6c0a112a8d..17a4bd05a02f 100644
--- a/arch/riscv/mm/pgtable.c
+++ b/arch/riscv/mm/pgtable.c
@@ -165,3 +165,19 @@ pud_t pudp_invalidate(struct vm_area_struct *vma, unsigned long address,
return old;
}
#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);
+}

--
2.43.0