Messages in this thread Patch in this message | | | From | Deepak Gupta <> | Subject | [PATCH v1 RFC Zisslpcfi 12/20] riscv mm: manufacture shadow stack pte and is vma shadowstack | Date | Sun, 12 Feb 2023 20:53:41 -0800 |
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This patch implements creating shadow stack pte (on riscv) if CONFIG_USER_SHADOW_STACK is selected. Creating shadow stack PTE on riscv means that clearing RWX and then setting W=1. Additionally this patch implements `arch_is_shadow_stack_vma`. Each arch can decide which combination of VMA flags are treated as shadow stack. riscv is choosing to following PTE encodings for VMA flags as well i.e. VM_WRITE only (no VM_READ or VM_EXEC) means its a shadow stack vma on riscv.
Signed-off-by: Deepak Gupta <debug@rivosinc.com> --- arch/riscv/include/asm/pgtable.h | 8 ++++++++ arch/riscv/mm/pageattr.c | 7 +++++++ 2 files changed, 15 insertions(+)
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h index 13b325253c99..11a423e78d52 100644 --- a/arch/riscv/include/asm/pgtable.h +++ b/arch/riscv/include/asm/pgtable.h @@ -344,6 +344,14 @@ static inline pte_t pte_mkwrite(pte_t pte) return __pte(pte_val(pte) | _PAGE_WRITE); } +#ifdef CONFIG_USER_SHADOW_STACK +static inline pte_t pte_mkshdwstk(pte_t pte) +{ + /* shadow stack on risc-v is XWR = 010. Clear everything and only set _PAGE_WRITE */ + return __pte((pte_val(pte) & ~(_PAGE_LEAF)) | _PAGE_WRITE); +} +#endif + /* static inline pte_t pte_mkexec(pte_t pte) */ static inline pte_t pte_mkdirty(pte_t pte) diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c index 86c56616e5de..582e17c4dc28 100644 --- a/arch/riscv/mm/pageattr.c +++ b/arch/riscv/mm/pageattr.c @@ -233,3 +233,10 @@ bool kernel_page_present(struct page *page) pte = pte_offset_kernel(pmd, addr); return pte_present(*pte); } + +#ifdef CONFIG_USER_SHADOW_STACK +bool arch_is_shadow_stack_vma(struct vm_area_struct *vma) +{ + return ((vma->vm_flags & (VM_WRITE | VM_READ | VM_EXEC)) == VM_WRITE); +} +#endif \ No newline at end of file -- 2.25.1
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