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    SubjectRe: [PATCH v4 11/39] x86/mm: Update pte_modify for _PAGE_COW
    On Fri, Dec 02, 2022 at 04:35:38PM -0800, Rick Edgecombe wrote:
    > From: Yu-cheng Yu <yu-cheng.yu@intel.com>
    >
    > The Write=0,Dirty=1 PTE has been used to indicate copy-on-write pages.
    > However, newer x86 processors also regard a Write=0,Dirty=1 PTE as a
    > shadow stack page. In order to separate the two, the software-defined
    > _PAGE_DIRTY is changed to _PAGE_COW for the copy-on-write case, and
    > pte_*() are updated to do this.
    >
    > pte_modify() takes a "raw" pgprot_t which was not necessarily created
    > with any of the existing PTE bit helpers. That means that it can return a
    > pte_t with Write=0,Dirty=1, a shadow stack PTE, when it did not intend to
    > create one.
    >
    > However pte_modify() changes a PTE to 'newprot', but it doesn't use the
    > pte_*(). Modify it to also move _PAGE_DIRTY to _PAGE_COW. Apply the same
    > changes to pmd_modify().
    >
    > Tested-by: Pengfei Xu <pengfei.xu@intel.com>
    > Tested-by: John Allen <john.allen@amd.com>
    > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>

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

    --
    Kees Cook

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