Re: [PATCH v25 18/30] mm/mmap: Add shadow stack pages to memory accounting

[Kirill A. Shutemov]

On Thu, Apr 15, 2021 at 03:14:07PM -0700, Yu-cheng Yu wrote:
> Account shadow stack pages to stack memory.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
> v25:
> - Remove #ifdef CONFIG_ARCH_HAS_SHADOW_STACK for is_shadow_stack_mapping().
> v24:
> - Change arch_shadow_stack_mapping() to is_shadow_stack_mapping().
> - Change VM_SHSTK to VM_SHADOW_STACK.
> 
>  arch/x86/include/asm/pgtable.h | 3 +++
>  arch/x86/mm/pgtable.c          | 5 +++++
>  include/linux/pgtable.h        | 9 +++++++++
>  mm/mmap.c                      | 5 +++++
>  4 files changed, 22 insertions(+)
> 
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index da5dea417663..7f324edaedfa 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -1692,6 +1692,9 @@ static inline bool arch_faults_on_old_pte(void)
>  #define maybe_mkwrite maybe_mkwrite
>  extern pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma);
>  
> +#define is_shadow_stack_mapping is_shadow_stack_mapping
> +extern bool is_shadow_stack_mapping(vm_flags_t vm_flags);
> +
>  #endif	/* __ASSEMBLY__ */
>  
>  #endif /* _ASM_X86_PGTABLE_H */
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> index e778dbbef3d8..69c0ef583c55 100644
> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -897,3 +897,8 @@ int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)
>  
>  #endif /* CONFIG_X86_64 */
>  #endif	/* CONFIG_HAVE_ARCH_HUGE_VMAP */
> +
> +bool is_shadow_stack_mapping(vm_flags_t vm_flags)
> +{
> +	return (vm_flags & VM_SHADOW_STACK);

Nit: parentheses are redundant.

> +}
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 5e772392a379..45b601fa1a1c 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -1446,6 +1446,15 @@ static inline bool arch_has_pfn_modify_check(void)
>  }
>  #endif /* !_HAVE_ARCH_PFN_MODIFY_ALLOWED */
>  
> +#ifdef CONFIG_MMU
> +#ifndef is_shadow_stack_mapping
> +static inline bool is_shadow_stack_mapping(vm_flags_t vm_flags)
> +{
> +	return false;
> +}
> +#endif
> +#endif /* CONFIG_MMU */

What the purpose #ifdef CONFIG_MMU? Looks redundant.

Otherwise: 

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

> +
>  /*
>   * Architecture PAGE_KERNEL_* fallbacks
>   *
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 3f287599a7a3..d77fb39b6ab5 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1718,6 +1718,9 @@ static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags)
>  	if (file && is_file_hugepages(file))
>  		return 0;
>  
> +	if (is_shadow_stack_mapping(vm_flags))
> +		return 1;
> +
>  	return (vm_flags & (VM_NORESERVE | VM_SHARED | VM_WRITE)) == VM_WRITE;
>  }
>  
> @@ -3387,6 +3390,8 @@ void vm_stat_account(struct mm_struct *mm, vm_flags_t flags, long npages)
>  		mm->stack_vm += npages;
>  	else if (is_data_mapping(flags))
>  		mm->data_vm += npages;
> +	else if (is_shadow_stack_mapping(flags))
> +		mm->stack_vm += npages;
>  }
>  
>  static vm_fault_t special_mapping_fault(struct vm_fault *vmf);
> -- 
> 2.21.0
> 
> 

-- 
 Kirill A. Shutemov