linux-kernel - Re: [PATCH v21 08/26] x86/mm: Introduce _PAGE

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Date:   Mon, 1 Mar 2021 10:59:44 -0800
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
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>,
        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 v21 08/26] x86/mm: Introduce _PAGE_COW

On 3/1/2021 7:52 AM, Borislav Petkov wrote:
> On Wed, Feb 17, 2021 at 02:27:12PM -0800, Yu-cheng Yu wrote:
>> @@ -182,7 +206,7 @@ static inline int pud_young(pud_t pud)
>>   
>>   static inline int pte_write(pte_t pte)
>>   {
>> -	return pte_flags(pte) & _PAGE_RW;
> 
> Put here a comment along the lines of:
> 
> 	/*
> 	 * Shadow stack pages are always writable - but not by normal
> 	 * instructions but only by shadow stack operations. Therefore, the
> 	 * W=0, D=1 test.
> 	 */
> 
> to make it clear what this means.
> 
>> +	return (pte_flags(pte) & _PAGE_RW) || pte_shstk(pte);
>>   }
>>   
>>   static inline int pte_huge(pte_t pte)
>> @@ -314,6 +338,24 @@ static inline pte_t pte_clear_flags(pte_t pte, pteval_t clear)
>>   	return native_make_pte(v & ~clear);
>>   }
>>   
>> +static inline pte_t pte_make_cow(pte_t pte)
> 
> pte_mkcow like the rest of the "pte_mkX" functions.
> 
> And below too, for the other newly added pXd_make_* helpers.
> 
> 
>>   static inline pmd_t pmd_mkdirty(pmd_t pmd)
>>   {
>> -	return pmd_set_flags(pmd, _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
>> +	pmdval_t dirty = _PAGE_DIRTY;
>> +
>> +	/* Avoid creating (HW)Dirty=1, Write=0 PMDs */
>> +	if (cpu_feature_enabled(X86_FEATURE_SHSTK) && !(pmd_flags(pmd) & _PAGE_RW))
> 
> 						      !(pmd_write(pmd))
> 
>> +		dirty = _PAGE_COW;
>> +
>> +	return pmd_set_flags(pmd, dirty | _PAGE_SOFT_DIRTY);
>> +}
> 
> ...
> 
>>   static inline pud_t pud_mkdirty(pud_t pud)
>>   {
>> -	return pud_set_flags(pud, _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
>> +	pudval_t dirty = _PAGE_DIRTY;
>> +
>> +	/* Avoid creating (HW)Dirty=1, Write=0 PUDs */
>> +	if (cpu_feature_enabled(X86_FEATURE_SHSTK) && !(pud_flags(pud) & _PAGE_RW))
> 
> 						      !(pud_write(pud))
> 
> 

I will update.  Thanks!

--
Yu-cheng