Re: [PATCH v3 12/29] riscv mmu: teach pte_mkwrite to manufacture shadow stack PTEs

Alexandre Ghiti
2024-05-12T16:30:33Z

On 04/04/2024 01:35, Deepak Gupta 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>
> ---
> 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 6362407f1e83..9b837239d3e8 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);
> @@ -694,6 +698,9 @@ 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 ef887efcb679..c84ae2e0424d 100644
> --- a/arch/riscv/mm/pgtable.c
> +++ b/arch/riscv/mm/pgtable.c
> @@ -142,3 +142,24 @@ 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 (vma_is_shadow_stack(vma->vm_flags))
> + return pte_mkwrite_shstk(pte);
> +
> + pte = pte_mkwrite_novma(pte);

I would directly return pte_mkwrite_novma(pte) instead of assigning pte.

> +
> + return pte;
> +}
> +
> +pmd_t pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
> +{
> + if (vma_is_shadow_stack(vma->vm_flags))
> + return pmd_mkwrite_shstk(pmd);
> +
> + pmd = pmd_mkwrite_novma(pmd);

Ditto here.

> +
> + return pmd;
> +}
> +

Otherwise:

Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Thanks,

Alex