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    Subject[PATCH 04/11] x86/espfix: document use of _PAGE_GLOBAL
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    From: Dave Hansen <dave.hansen@linux.intel.com>

    The "normal" kernel page table creation mechanisms using
    PAGE_KERNEL_* page protections will never set _PAGE_GLOBAL with PTI.
    The few places in the kernel that always want _PAGE_GLOBAL must
    avoid using PAGE_KERNEL_*.

    Document that we want it here and its use is not accidental.

    Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Kees Cook <keescook@google.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Juergen Gross <jgross@suse.com>
    Cc: x86@kernel.org
    Cc: Nadav Amit <namit@vmware.com>
    ---

    b/arch/x86/kernel/espfix_64.c | 4 ++++
    1 file changed, 4 insertions(+)

    diff -puN arch/x86/kernel/espfix_64.c~espfix-use-kern-defaults-not-supported arch/x86/kernel/espfix_64.c
    --- a/arch/x86/kernel/espfix_64.c~espfix-use-kern-defaults-not-supported 2018-04-06 10:47:55.343796126 -0700
    +++ b/arch/x86/kernel/espfix_64.c 2018-04-06 10:47:55.346796126 -0700
    @@ -195,6 +195,10 @@ void init_espfix_ap(int cpu)

    pte_p = pte_offset_kernel(&pmd, addr);
    stack_page = page_address(alloc_pages_node(node, GFP_KERNEL, 0));
    + /*
    + * __PAGE_KERNEL_* includes _PAGE_GLOBAL, which we want since
    + * this is mapped to userspace.
    + */
    pte = __pte(__pa(stack_page) | ((__PAGE_KERNEL_RO | _PAGE_ENC) & ptemask));
    for (n = 0; n < ESPFIX_PTE_CLONES; n++)
    set_pte(&pte_p[n*PTE_STRIDE], pte);
    _
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