Re: [PATCH v24 15/30] x86/mm: Update maybe_mkwrite() for shadow stack

[Kirill A. Shutemov]

On Thu, Apr 01, 2021 at 03:10:49PM -0700, Yu-cheng Yu wrote:
> When serving a page fault, maybe_mkwrite() makes a PTE writable if its vma
> has VM_WRITE.
> 
> A shadow stack vma has VM_SHADOW_STACK.  Its PTEs have _PAGE_DIRTY, but not
> _PAGE_WRITE.  In fork(), _PAGE_DIRTY is cleared to cause copy-on-write,
> and in the page fault handler, _PAGE_DIRTY is restored and the shadow stack
> page is writable again.
> 
> Introduce an x86 version of maybe_mkwrite(), which sets proper PTE bits
> according to VM flags.
> 
> Apply the same changes to maybe_pmd_mkwrite().
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
> v24:
> - Instead of doing arch_maybe_mkwrite(), overwrite maybe*_mkwrite() with x86
>   versions.
> - Change VM_SHSTK to VM_SHADOW_STACK.
> 
>  arch/x86/include/asm/pgtable.h |  8 ++++++++
>  arch/x86/mm/pgtable.c          | 20 ++++++++++++++++++++
>  include/linux/mm.h             |  2 ++
>  mm/huge_memory.c               |  2 ++
>  4 files changed, 32 insertions(+)
> 
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index 46d9394b884f..51cdf14488b7 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -1686,6 +1686,14 @@ static inline bool arch_faults_on_old_pte(void)
>  	return false;
>  }
>  
> +#define maybe_mkwrite maybe_mkwrite
> +extern pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma);
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +#define maybe_pmd_mkwrite maybe_pmd_mkwrite
> +extern pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma);
> +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

Move it next to other THP-depended stuff.

Otherwise looks good to me:

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

-- 
 Kirill A. Shutemov