[RFC v1 4/4] x86, boot: Memory hotplug support for KASLR memory randomization

[Thomas Garnier]

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 
---
Based on next-20160413
---
 arch/x86/Kconfig| 15 +++
 arch/x86/mm/kaslr.c | 14 --
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7c786d4..cc01b69 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2018,6 +2018,21 @@ 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 9de807d..f7dc477 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -63,7 +63,7 @@ void __init kernel_randomize_memory(void)
 {
size_t i;
unsigned long addr = memory_rand_start;
-   unsigned long padding, rand, mem_tb;
+   unsigned long padding, rand, mem_tb, page_offset_padding;
struct rnd_state rnd_st;
unsigned long remain_padding = memory_rand_end - memory_rand_start;
 
@@ -74,8 +74,18 @@ void __init kernel_randomize_memory(void)
if (!xen_domain())
page_offset_base -= __XEN_SPACE;
 
+   /*
+* Update Physical memory mapping to available and
+* add padding if needed (especially for memory hotplug support).
+*/
+   page_offset_padding = CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
+
+#ifdef CONFIG_MEMORY_HOTPLUG
+   page_offset_padding = max(1UL, page_offset_padding);
+#endif
+
BUG_ON(kaslr_regions[0].base != _offset_base);
-   mem_tb = ((max_pfn << PAGE_SHIFT) >> TB_SHIFT);
+   mem_tb = ((max_pfn << PAGE_SHIFT) >> TB_SHIFT) + page_offset_padding;
 
if (mem_tb < kaslr_regions[0].size_tb)
kaslr_regions[0].size_tb = mem_tb;
-- 
2.8.0.rc3.226.g39d4020

[RFC v1 4/4] x86, boot: Memory hotplug support for KASLR memory randomization

[Thomas Garnier]

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 
---
Based on next-20160413
---
 arch/x86/Kconfig| 15 +++
 arch/x86/mm/kaslr.c | 14 --
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7c786d4..cc01b69 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2018,6 +2018,21 @@ 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 9de807d..f7dc477 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -63,7 +63,7 @@ void __init kernel_randomize_memory(void)
 {
size_t i;
unsigned long addr = memory_rand_start;
-   unsigned long padding, rand, mem_tb;
+   unsigned long padding, rand, mem_tb, page_offset_padding;
struct rnd_state rnd_st;
unsigned long remain_padding = memory_rand_end - memory_rand_start;
 
@@ -74,8 +74,18 @@ void __init kernel_randomize_memory(void)
if (!xen_domain())
page_offset_base -= __XEN_SPACE;
 
+   /*
+* Update Physical memory mapping to available and
+* add padding if needed (especially for memory hotplug support).
+*/
+   page_offset_padding = CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
+
+#ifdef CONFIG_MEMORY_HOTPLUG
+   page_offset_padding = max(1UL, page_offset_padding);
+#endif
+
BUG_ON(kaslr_regions[0].base != _offset_base);
-   mem_tb = ((max_pfn << PAGE_SHIFT) >> TB_SHIFT);
+   mem_tb = ((max_pfn << PAGE_SHIFT) >> TB_SHIFT) + page_offset_padding;
 
if (mem_tb < kaslr_regions[0].size_tb)
kaslr_regions[0].size_tb = mem_tb;
-- 
2.8.0.rc3.226.g39d4020