Message-ID: <63f288cc.a70a0220.5558c.3c92@mx.google.com>
Date:   Sun, 19 Feb 2023 12:38:35 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc:     x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
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        linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Balbir Singh <bsingharora@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
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        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
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        eranian@google.com, rppt@kernel.org, jamorris@linux.microsoft.com,
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        linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org,
        xen-devel@lists.xenproject.org
Subject: Re: [PATCH v6 11/41] mm: Introduce pte_mkwrite_kernel()
References: <20230218211433.26859-1-rick.p.edgecombe@intel.com>
 <20230218211433.26859-12-rick.p.edgecombe@intel.com>
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In-Reply-To: <20230218211433.26859-12-rick.p.edgecombe@intel.com>
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On Sat, Feb 18, 2023 at 01:14:03PM -0800, Rick Edgecombe wrote:
> The x86 Control-flow Enforcement Technology (CET) feature includes a new
> type of memory called shadow stack. This shadow stack memory has some
> unusual properties, which requires some core mm changes to function
> properly.
> 
> One of these changes is to allow for pte_mkwrite() to create different
> types of writable memory (the existing conventionally writable type and
> also the new shadow stack type). Future patches will convert pte_mkwrite()
> to take a VMA in order to facilitate this, however there are places in the
> kernel where pte_mkwrite() is called outside of the context of a VMA.
> These are for kernel memory. So create a new variant called
> pte_mkwrite_kernel() and switch the kernel users over to it. Have
> pte_mkwrite() and pte_mkwrite_kernel() be the same for now. Future patches
> will introduce changes to make pte_mkwrite() take a VMA.
> 
> Only do this for architectures that need it because they call pte_mkwrite()
> in arch code without an associated VMA. Since it will only currently be
> used in arch code, so do not include it in arch_pgtable_helpers.rst.
> 
> Cc: linux-doc@vger.kernel.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-s390@vger.kernel.org
> Cc: xen-devel@lists.xenproject.org
> Cc: linux-arch@vger.kernel.org
> Cc: linux-mm@kvack.org
> Tested-by: Pengfei Xu <pengfei.xu@intel.com>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>

I think it's a little weird that it's the only PTE helper taking a vma,
but it does seem like the right approach.

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

-- 
Kees Cook