Re: [PATCH v11 08/27] riscv mmu: teach pte_mkwrite to manufacture shadow stack PTEs

[Zong Li <zong.li@sifive.com>]

On Mon, Mar 10, 2025 at 11:42 PM Deepak Gupta <debug@rivosinc.com> wrote:
>
> 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 ede43185ffdf..ccd2fa34afb8 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -416,6 +416,10 @@ 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);
> @@ -749,6 +753,9 @@ 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 4ae67324f992..be5d38546bb3 100644
> --- a/arch/riscv/mm/pgtable.c
> +++ b/arch/riscv/mm/pgtable.c
> @@ -155,3 +155,20 @@ 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);
> +}
> +
>
LGTM.

Reviewed-by: Zong Li <zong.li@sifive.com>
> --
> 2.34.1
>
>
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