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

Yu, Yu-cheng
2021-03-26T15:47:21Z

On 3/22/2021 3:57 AM, Kirill A. Shutemov wrote:
> 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.
>

The thought was, here all testings are done with helpers, e.g.
is_data_mapping(), so creating a helper for shadow stack is more inline
with the existing code. Or, maybe we can call it
is_shadow_stack_mapping()? And, since we have a helper, use it in
accountable_mapping() as well. Or do you have other suggestions?

Thanks,
Yu-cheng