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Date:   Mon, 3 Oct 2022 11:24:07 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc:     x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
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        jamorris@linux.microsoft.com, dethoma@microsoft.com,
        Yu-cheng Yu <yu-cheng.yu@intel.com>
Subject: Re: [PATCH v2 17/39] mm: Fixup places that call pte_mkwrite()
 directly
Message-ID: <202210031124.81D807B6B@keescook>
References: <20220929222936.14584-1-rick.p.edgecombe@intel.com>
 <20220929222936.14584-18-rick.p.edgecombe@intel.com>
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On Thu, Sep 29, 2022 at 03:29:14PM -0700, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@intel.com>
> 
> With the introduction of shadow stack memory there are two ways a pte can
> be writable: regular writable memory and shadow stack memory.
> 
> In past patches, maybe_mkwrite() has been updated to apply pte_mkwrite()
> or pte_mkwrite_shstk() depending on the VMA flag. This covers most cases
> where a PTE is made writable. However, there are places where pte_mkwrite()
> is called directly and the logic should now also create a shadow stack PTE
> in the case of a shadow stack VMA.
> 
>  - do_anonymous_page() and migrate_vma_insert_page() check VM_WRITE
>    directly and call pte_mkwrite(), which is the same as maybe_mkwrite()
>    in logic and intention. Just change them to maybe_mkwrite().
> 
>  - When userfaultfd is creating a PTE after userspace handles the fault
>    it calls pte_mkwrite() directly. Teach it about pte_mkwrite_shstk()
> 
> In other cases where pte_mkwrite() is called directly, the VMA will not
> be VM_SHADOW_STACK, and so shadow stack memory should not be created.
>  - In the case of pte_savedwrite(), shadow stack VMA's are excluded.
>  - In the case of the "dirty_accountable" optimization in mprotect(),
>    shadow stack VMA's won't be VM_SHARED, so it is not nessary.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>

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

-- 
Kees Cook