linux-kernel - Re: [PATCH v21 10/26] x86/mm: Update pte_modify for _PAGE

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Message-ID: <20210305142940.GC2685@zn.tnic>
Date:   Fri, 5 Mar 2021 15:29:40 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
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 10/26] x86/mm: Update pte_modify for _PAGE_COW

On Wed, Feb 17, 2021 at 02:27:14PM -0800, Yu-cheng Yu wrote:
> @@ -787,16 +802,34 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
>  	 */
>  	val &= _PAGE_CHG_MASK;
>  	val |= check_pgprot(newprot) & ~_PAGE_CHG_MASK;
> +	val = fixup_dirty_pte(val);

Do I see it correctly that you can do here and below:

	/*
	 * Fix up potential shadow stack page flags because the RO, Dirty PTE is
	 * special.
	 */
	if (pte_dirty()) {
		pte_mkclean();
		pte_mkdirty();
	}

?

That fixup thing looks grafted and not like a normal flow to me.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette