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

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Date: Sun, 12 May 2024 18:28:59 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: Deepak Gupta <debug@...osinc.com>, paul.walmsley@...ive.com,
 rick.p.edgecombe@...el.com, broonie@...nel.org, Szabolcs.Nagy@....com,
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Subject: Re: [PATCH v3 12/29] riscv mmu: teach pte_mkwrite to manufacture
 shadow stack PTEs


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@...osinc.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@...osinc.com>

Thanks,

Alex