From: Thomas Garnier <thgarnie@xxxxxxxxxx> 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@xxxxxxxxxx> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- 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 adab3fef3bb4..214b3fadbc11 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2010,6 +2010,21 @@ 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 terabytes 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 4f91dc273062..3e9875f7fdda 100644 --- a/arch/x86/mm/kaslr.c +++ b/arch/x86/mm/kaslr.c @@ -114,8 +114,13 @@ void __init kernel_randomize_memory(void) if (!kaslr_memory_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); - memory_tb = ((max_pfn << PAGE_SHIFT) >> TB_SHIFT); + memory_tb = ((max_pfn << PAGE_SHIFT) >> TB_SHIFT) + + CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING; /* Adapt phyiscal memory region size based on available memory */ if (memory_tb < kaslr_regions[0].size_tb) -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
