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Subject[PATCH v3 5/5] x86/mm/KASLR: Adjust the padding size for the direct mapping.
Date
From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>

The system sometimes crashes while memory hot-adding on KASLR
enabled system. The crash happens because the regions pointed by
kaslr_regions[].base are overwritten by the hot-added memory.

It happens because of the padding size for kaslr_regions[].base isn't
enough for the system whose physical memory layout has huge space for
memory hotplug. kaslr_regions[].base points "actual installed
memory size + padding" or higher address. So, if the "actual + padding"
is lower address than the maximum memory address, which means the memory
address reachable by memory hot-add, kaslr_regions[].base is destroyed by
the overwritten.

address
^
|------- maximum memory address (Hotplug)
| ^
|------- kaslr_regions[0].base | Hotadd-able region
| ^ |
| | padding |
| V V
|------- actual memory address (Installed on boot)
|

Fix it by getting the maximum memory address from SRAT and store
the value in boot_param, then set the padding size while KASLR
initializing if the default padding size isn't enough.

Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
---
arch/x86/mm/kaslr.c | 31 +++++++++++++++++++++++++++++--
1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index 8e5f3642e..a78844c57 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -70,6 +70,34 @@ static inline bool kaslr_memory_enabled(void)
return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
}

+static inline unsigned long phys_memmap_size(void)
+{
+ unsigned long padding = CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
+#ifdef CONFIG_MEMORY_HOTPLUG
+ unsigned long actual, maximum, base;
+
+ if (!boot_params.max_addr)
+ goto out;
+
+ /*
+ * The padding size should set to get for kaslr_regions[].base
+ * bigger address than the maximum memory address the system can
+ * have. kaslr_regions[].base points "actual size + padding" or
+ * higher address. If "actual size + padding" points the lower
+ * address than the maximum memory size, fix the padding size.
+ */
+ actual = roundup(PFN_PHYS(max_pfn), 1UL << TB_SHIFT);
+ maximum = roundup(boot_params.max_addr, 1UL << TB_SHIFT);
+ base = actual + (padding << TB_SHIFT);
+
+ if (maximum > base)
+ padding = (maximum - actual) >> TB_SHIFT;
+out:
+#endif
+ return DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
+ padding;
+}
+
/*
* Even though a huge virtual address space is reserved for the direct
* mapping of physical memory, e.g in 4-level paging mode, it's 64TB,
@@ -87,8 +115,7 @@ static inline unsigned long calc_direct_mapping_size(void)
* Update Physical memory mapping to available and
* add padding if needed (especially for memory hotplug support).
*/
- memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
- CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
+ memory_tb = phys_memmap_size();

size_tb = 1 << (MAX_PHYSMEM_BITS - TB_SHIFT);

--
2.18.1
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