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    Subject[PATCH 4.15 054/146] arm64: mm: fix thinko in non-global page table attribute check
    Date
    4.15-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Ard Biesheuvel <ard.biesheuvel@linaro.org>

    commit 753e8abc36b2c966caea075db0c845563c8a19bf upstream.

    The routine pgattr_change_is_safe() was extended in commit 4e6020565596
    ("arm64: mm: Permit transitioning from Global to Non-Global without BBM")
    to permit changing the nG attribute from not set to set, but did so in a
    way that inadvertently disallows such changes if other permitted attribute
    changes take place at the same time. So update the code to take this into
    account.

    Fixes: 4e6020565596 ("arm64: mm: Permit transitioning from Global to ...")
    Cc: <stable@vger.kernel.org> # 4.14.x-
    Acked-by: Mark Rutland <mark.rutland@arm.com>
    Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
    Acked-by: Will Deacon <will.deacon@arm.com>
    Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
    Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/arm64/mm/mmu.c | 8 ++++----
    1 file changed, 4 insertions(+), 4 deletions(-)

    --- a/arch/arm64/mm/mmu.c
    +++ b/arch/arm64/mm/mmu.c
    @@ -107,7 +107,7 @@ static bool pgattr_change_is_safe(u64 ol
    * The following mapping attributes may be updated in live
    * kernel mappings without the need for break-before-make.
    */
    - static const pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE;
    + static const pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;

    /* creating or taking down mappings is always safe */
    if (old == 0 || new == 0)
    @@ -117,9 +117,9 @@ static bool pgattr_change_is_safe(u64 ol
    if ((old | new) & PTE_CONT)
    return false;

    - /* Transitioning from Global to Non-Global is safe */
    - if (((old ^ new) == PTE_NG) && (new & PTE_NG))
    - return true;
    + /* Transitioning from Non-Global to Global is unsafe */
    + if (old & ~new & PTE_NG)
    + return false;

    return ((old ^ new) & ~mask) == 0;
    }

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