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

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Message-ID: <ZkJO7mlAYqVwDYt6@debug.ba.rivosinc.com>
Date: Mon, 13 May 2024 10:33:34 -0700
From: Deepak Gupta <debug@...osinc.com>
To: Alexandre Ghiti <alex@...ti.fr>
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Subject: Re: [PATCH v3 12/29] riscv mmu: teach pte_mkwrite to manufacture
 shadow stack PTEs

On Sun, May 12, 2024 at 06:28:59PM +0200, Alexandre Ghiti wrote:
>
>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.

noted.

>
>
>>+
>>+	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.

noted here too.

>
>
>>+
>>+	return pmd;
>>+}
>>+
>
>
>Otherwise:
>
>Reviewed-by: Alexandre Ghiti <alexghiti@...osinc.com>
>
>Thanks,
>
>Alex
>