Re: [PATCH v23 18/28] mm/mmap: Add shadow stack pages to memory accounting

Kirill A. Shutemov
2021-03-22T10:57:25Z

On Tue, Mar 16, 2021 at 08:10:44AM -0700, Yu-cheng Yu wrote:
> Account shadow stack pages to stack memory.
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> ---
> arch/x86/mm/pgtable.c | 7 +++++++
> include/linux/pgtable.h | 11 +++++++++++
> mm/mmap.c | 5 +++++
> 3 files changed, 23 insertions(+)
>
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> index 0f4fbf51a9fc..948d28c29964 100644
> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -895,3 +895,10 @@ int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)
>
> #endif /* CONFIG_X86_64 */
> #endif /* CONFIG_HAVE_ARCH_HUGE_VMAP */
> +
> +#ifdef CONFIG_ARCH_HAS_SHADOW_STACK
> +bool arch_shadow_stack_mapping(vm_flags_t vm_flags)
> +{
> + return (vm_flags & VM_SHSTK);
> +}
> +#endif
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index cbd98484c4f1..487c08df4365 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -1470,6 +1470,17 @@ static inline pmd_t arch_maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma
> #endif /* CONFIG_ARCH_MAYBE_MKWRITE */
> #endif /* CONFIG_MMU */
>
> +#ifdef CONFIG_MMU
> +#ifdef CONFIG_ARCH_HAS_SHADOW_STACK
> +bool arch_shadow_stack_mapping(vm_flags_t vm_flags);
> +#else
> +static inline bool arch_shadow_stack_mapping(vm_flags_t vm_flags)
> +{
> + return false;
> +}
> +#endif /* CONFIG_ARCH_HAS_SHADOW_STACK */
> +#endif /* CONFIG_MMU */
> +
> /*
> * Architecture PAGE_KERNEL_* fallbacks
> *
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 3f287599a7a3..2ac67882ace2 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 (arch_shadow_stack_mapping(vm_flags))
> + return 1;
> +

What's wrong with testing (vm_flags & VM_SHSTK) here? VM_SHSTK is 0 on
non-x86.

> 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 (arch_shadow_stack_mapping(flags))
> + mm->stack_vm += npages;

Ditto.

> }
>
> static vm_fault_t special_mapping_fault(struct vm_fault *vmf);
> --
> 2.21.0
>

--
Kirill A. Shutemov