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 <thgar...@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
