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

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Date:   Fri, 26 Mar 2021 08:46:30 -0700
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>,
        Haitao Huang <haitao.huang@...el.com>
Subject: Re: [PATCH v23 18/28] mm/mmap: Add shadow stack pages to memory
 accounting

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@...el.com>
>> Reviewed-by: Kees Cook <keescook@...omium.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