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    Subject[PATCH v5 4/4] x86, boot: Memory hotplug support for KASLR memory randomization
    Date
    Add a new option (CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING) to define
    the padding used for the physical memory mapping section when KASLR
    memory is enabled. It ensures there is enough virtual address space when
    CONFIG_MEMORY_HOTPLUG is used. The default value is 10 terabytes. If
    CONFIG_MEMORY_HOTPLUG is not used, no space is reserved increasing the
    entropy available.

    Signed-off-by: Thomas Garnier <thgarnie@google.com>
    ---
    Based on next-20160511
    ---
    arch/x86/Kconfig | 15 +++++++++++++++
    arch/x86/mm/kaslr.c | 7 ++++++-
    2 files changed, 21 insertions(+), 1 deletion(-)

    diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    index f5ed150..0e5087d 100644
    --- a/arch/x86/Kconfig
    +++ b/arch/x86/Kconfig
    @@ -2005,6 +2005,21 @@ config RANDOMIZE_MEMORY

    If unsure, say N.

    +config RANDOMIZE_MEMORY_PHYSICAL_PADDING
    + hex "Physical memory mapping padding" if EXPERT
    + depends on RANDOMIZE_MEMORY
    + default "0xa" if MEMORY_HOTPLUG
    + default "0x0"
    + range 0x1 0x40 if MEMORY_HOTPLUG
    + range 0x0 0x40
    + ---help---
    + Define the padding in terabyte added to the existing physical memory
    + size during kernel memory randomization. It is useful for memory
    + hotplug support but reduces the entropy available for address
    + randomization.
    +
    + If unsure, leave at the default value.
    +
    config HOTPLUG_CPU
    bool "Support for hot-pluggable CPUs"
    depends on SMP
    diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
    index 2415178..5e86082 100644
    --- a/arch/x86/mm/kaslr.c
    +++ b/arch/x86/mm/kaslr.c
    @@ -88,8 +88,13 @@ void __init kernel_randomize_memory(void)
    if (!kaslr_enabled())
    return;

    + /*
    + * Update Physical memory mapping to available and
    + * add padding if needed (especially for memory hotplug support).
    + */
    BUG_ON(kaslr_regions[0].base != &page_offset_base);
    - mem_tb = ((max_pfn << PAGE_SHIFT) >> TB_SHIFT);
    + mem_tb = ((max_pfn << PAGE_SHIFT) >> TB_SHIFT) +
    + CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;

    if (mem_tb < kaslr_regions[0].size_tb)
    kaslr_regions[0].size_tb = mem_tb;
    --
    2.8.0.rc3.226.g39d4020
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