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    Subject[PATCH] [4/8] CPA: Fix set_memory_x for ioremap
    Date

    EFI currently calls set_memory_x() on potentially ioremapped addresses.

    This is problematic for several reasons:

    - The cpa code internally calls __pa on it which does not work for remapped
    addresses and will give some random result.
    - cpa will try to change all potential aliases (like the kernel mapping
    on x86-64), but that is not needed for NX because the caller does only needs its
    specific virtual address executable. There is no requirement in the x86 architecture
    for nx bits to be coherent between mapping aliases. Also with the
    previous problem of __pa returning a wrong address it would likely try to change
    some random other page if you're unlucky and the random result would
    match the kernel text range.

    There would be several possible ways to fix this:
    - Simply don't set the NX bit in the original ioremap and drop
    set_memory_x and add a ioremap_exec(). That would be my preferred solution,
    but unfortunately has been dismissed before
    - Drop all __pas and always use the physical address derived
    from the looked up PTE. This would need some significant restructuring
    and would only fix the first problem above, not the second.
    - Special case NX clear to change any aliases. I chose this one
    because it happens to fix both problems, so is both a fix
    and a optimization.

    This implies that it's still not safe calling set_memory_(not x) on
    any ioremaped/vmalloced/module addresses.

    I don't have a EFI system so this is untested.

    Cc: ying.huang@intel.com

    Signed-off-by: Andi Kleen <ak@suse.de>

    ---
    arch/x86/mm/pageattr.c | 7 +++++--
    1 file changed, 5 insertions(+), 2 deletions(-)

    Index: linux/arch/x86/mm/pageattr.c
    ===================================================================
    --- linux.orig/arch/x86/mm/pageattr.c
    +++ linux/arch/x86/mm/pageattr.c
    @@ -28,6 +28,7 @@ struct cpa_data {
    pgprot_t mask_clr;
    int numpages;
    int flushtlb;
    + int addronly;
    };

    static inline int
    @@ -602,7 +603,7 @@ static int change_page_attr_addr(struct
    * fixup the low mapping first. __va() returns the virtual
    * address in the linear mapping:
    */
    - if (within(address, HIGH_MAP_START, HIGH_MAP_END))
    + if (within(address, HIGH_MAP_START, HIGH_MAP_END) && !cpa->addronly)
    address = (unsigned long) __va(phys_addr);
    #endif

    @@ -615,7 +616,7 @@ static int change_page_attr_addr(struct
    * If the physical address is inside the kernel map, we need
    * to touch the high mapped kernel as well:
    */
    - if (within(phys_addr, 0, KERNEL_TEXT_SIZE)) {
    + if (!cpa->addronly && within(phys_addr, 0, KERNEL_TEXT_SIZE)) {
    /*
    * Calc the high mapping address. See __phys_addr()
    * for the non obvious details.
    @@ -695,6 +696,8 @@ static int change_page_attr_set_clr(unsi
    cpa.mask_set = mask_set;
    cpa.mask_clr = mask_clr;
    cpa.flushtlb = 0;
    + cpa.addronly = !pgprot_val(mask_set) &&
    + pgprot_val(mask_clr) == _PAGE_NX;

    ret = __change_page_attr_set_clr(&cpa);


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