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    Subject[PATCH v2 08/39] x86/mm: Remove _PAGE_DIRTY from kernel RO pages
    Date
    From: Yu-cheng Yu <yu-cheng.yu@intel.com>

    Processors sometimes directly create Write=0,Dirty=1 PTEs. These PTEs are
    created by software. One such case is that kernel read-only pages are
    historically set up as Dirty.

    New processors that support Shadow Stack regard Write=0,Dirty=1 PTEs as
    shadow stack pages. When CR4.CET=1 and IA32_S_CET.SH_STK_EN=1, some
    instructions can write to such supervisor memory. The kernel does not set
    IA32_S_CET.SH_STK_EN, but to reduce ambiguity between shadow stack and
    regular Write=0 pages, removed Dirty=1 from any kernel Write=0 PTEs.

    Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
    Co-developed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
    Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: Kees Cook <keescook@chromium.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Dave Hansen <dave.hansen@linux.intel.com>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Peter Zijlstra <peterz@infradead.org>

    ---

    v2:
    - Normalize PTE bit descriptions between patches

    arch/x86/include/asm/pgtable_types.h | 6 +++---
    arch/x86/mm/pat/set_memory.c | 2 +-
    2 files changed, 4 insertions(+), 4 deletions(-)

    diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
    index aa174fed3a71..ff82237e7b6b 100644
    --- a/arch/x86/include/asm/pgtable_types.h
    +++ b/arch/x86/include/asm/pgtable_types.h
    @@ -192,10 +192,10 @@ enum page_cache_mode {
    #define _KERNPG_TABLE (__PP|__RW| 0|___A| 0|___D| 0| 0| _ENC)
    #define _PAGE_TABLE_NOENC (__PP|__RW|_USR|___A| 0|___D| 0| 0)
    #define _PAGE_TABLE (__PP|__RW|_USR|___A| 0|___D| 0| 0| _ENC)
    -#define __PAGE_KERNEL_RO (__PP| 0| 0|___A|__NX|___D| 0|___G)
    -#define __PAGE_KERNEL_ROX (__PP| 0| 0|___A| 0|___D| 0|___G)
    +#define __PAGE_KERNEL_RO (__PP| 0| 0|___A|__NX| 0| 0|___G)
    +#define __PAGE_KERNEL_ROX (__PP| 0| 0|___A| 0| 0| 0|___G)
    #define __PAGE_KERNEL_NOCACHE (__PP|__RW| 0|___A|__NX|___D| 0|___G| __NC)
    -#define __PAGE_KERNEL_VVAR (__PP| 0|_USR|___A|__NX|___D| 0|___G)
    +#define __PAGE_KERNEL_VVAR (__PP| 0|_USR|___A|__NX| 0| 0|___G)
    #define __PAGE_KERNEL_LARGE (__PP|__RW| 0|___A|__NX|___D|_PSE|___G)
    #define __PAGE_KERNEL_LARGE_EXEC (__PP|__RW| 0|___A| 0|___D|_PSE|___G)
    #define __PAGE_KERNEL_WP (__PP|__RW| 0|___A|__NX|___D| 0|___G| __WP)
    diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
    index 1abd5438f126..ed9193b469ba 100644
    --- a/arch/x86/mm/pat/set_memory.c
    +++ b/arch/x86/mm/pat/set_memory.c
    @@ -1977,7 +1977,7 @@ int set_memory_nx(unsigned long addr, int numpages)

    int set_memory_ro(unsigned long addr, int numpages)
    {
    - return change_page_attr_clear(&addr, numpages, __pgprot(_PAGE_RW), 0);
    + return change_page_attr_clear(&addr, numpages, __pgprot(_PAGE_RW | _PAGE_DIRTY), 0);
    }

    int set_memory_rw(unsigned long addr, int numpages)
    --
    2.17.1
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