Re: [PATCH v2 16/39] x86/mm: Update maybe_mkwrite() for shadow stack
From: Peter Zijlstra <peterz@infradead.org>
Date: 2022-10-14 15:34:02
Also in:
linux-arch, linux-doc, linux-mm, lkml
On Thu, Sep 29, 2022 at 03:29:13PM -0700, Rick Edgecombe wrote:
quoted hunk ↗ jump to hunk
diff --git a/include/linux/mm.h b/include/linux/mm.h index 8cd413c5a329..fef14ab3abcb 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h@@ -981,13 +981,25 @@ void free_compound_page(struct page *page); * servicing faults for write access. In the normal case, do always want * pte_mkwrite. But get_user_pages can cause write faults for mappings * that do not have writing enabled, when used by access_process_vm. + * + * If a vma is shadow stack (a type of writable memory), mark the pte shadow + * stack. */ +#ifndef maybe_mkwrite static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma) { - if (likely(vma->vm_flags & VM_WRITE)) + if (!(vma->vm_flags & VM_WRITE)) + goto out; + + if (vma->vm_flags & VM_SHADOW_STACK) + pte = pte_mkwrite_shstk(pte); + else pte = pte_mkwrite(pte); + +out: return pte; } +#endif
Why the #ifndef guard? There is no other implementation, nor does this
patch introduce one.
Also, wouldn't it be simpler to write it like:
static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
{
if (!(vma->vm_flags & VM_WRITE))
return pte;
if (vma->vm_flags & VM_SHADOW_STACK)
return pte_mkwrite_shstk(pte);
return pte_mkwrite(pte);
}
? (idem for the pmd version etc..)