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Date:   Thu, 4 Feb 2021 12:20:17 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc:     x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Arnd Bergmann <arnd@arndb.de>,
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        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
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        Mike Kravetz <mike.kravetz@oracle.com>,
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        Randy Dunlap <rdunlap@infradead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
        Dave Martin <Dave.Martin@arm.com>,
        Weijiang Yang <weijiang.yang@intel.com>,
        Pengfei Xu <pengfei.xu@intel.com>
Subject: Re: [PATCH v19 10/25] x86/mm: Update pte_modify for _PAGE_COW
Message-ID: <202102041220.17A5BFD5BB@keescook>
References: <20210203225547.32221-1-yu-cheng.yu@intel.com>
 <20210203225547.32221-11-yu-cheng.yu@intel.com>
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In-Reply-To: <20210203225547.32221-11-yu-cheng.yu@intel.com>
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On Wed, Feb 03, 2021 at 02:55:32PM -0800, Yu-cheng Yu wrote:
> The read-only and Dirty PTE has been used to indicate copy-on-write pages.
> However, newer x86 processors also regard a read-only and Dirty PTE as a
> shadow stack page.  In order to separate the two, the software-defined
> _PAGE_COW is created to replace _PAGE_DIRTY for the copy-on-write case, and
> pte_*() are updated.
> 
> Pte_modify() changes a PTE to 'newprot', but it doesn't use the pte_*().
> Introduce fixup_dirty_pte(), which sets a dirty PTE, based on _PAGE_RW,
> to either _PAGE_DIRTY or _PAGE_COW.
> 
> Apply the same changes to pmd_modify().
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook