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Subject[PATCH v5 4/4] 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: Baoquan He <bhe@redhat.com>
Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
---
arch/x86/mm/kaslr.c | 57 +++++++++++++++++++++++++++++++++------------
1 file changed, 42 insertions(+), 15 deletions(-)

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index dc6182eecefa..1f0aa9e68226 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -70,15 +70,52 @@ static inline bool kaslr_memory_enabled(void)
return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
}

+/*
+ * 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,
+ * rare system can own enough physical memory to use it up, most are
+ * even less than 1TB. So with KASLR enabled, we adapt the size of
+ * direct mapping area to the size of actual physical memory plus the
+ * configured padding CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING.
+ * The left part will be taken out to join memory randomization.
+ */
+static inline unsigned long calc_direct_mapping_size(void)
+{
+ unsigned long size_tb, memory_tb;
+
+ memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
+ CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
+
+#ifdef CONFIG_MEMORY_HOTPLUG
+ if (boot_params.max_addr) {
+ unsigned long maximum_tb;
+
+ maximum_tb = DIV_ROUND_UP(boot_params.max_addr,
+ 1UL << TB_SHIFT);
+
+ if (maximum_tb > memory_tb)
+ memory_tb = maximum_tb;
+ }
+#endif
+ size_tb = 1 << (MAX_PHYSMEM_BITS - TB_SHIFT);
+
+ /*
+ * Adapt physical memory region size based on available memory
+ */
+ if (memory_tb < size_tb)
+ size_tb = memory_tb;
+
+ return size_tb;
+}
+
/* Initialize base and padding for each memory region randomized with KASLR */
void __init kernel_randomize_memory(void)
{
- size_t i;
- unsigned long vaddr_start, vaddr;
- unsigned long rand, memory_tb;
- struct rnd_state rand_state;
+ unsigned long vaddr_start, vaddr, rand;
unsigned long remain_entropy;
unsigned long vmemmap_size;
+ struct rnd_state rand_state;
+ size_t i;

vaddr_start = pgtable_l5_enabled() ? __PAGE_OFFSET_BASE_L5 : __PAGE_OFFSET_BASE_L4;
vaddr = vaddr_start;
@@ -95,20 +132,10 @@ void __init kernel_randomize_memory(void)
if (!kaslr_memory_enabled())
return;

- kaslr_regions[0].size_tb = 1 << (MAX_PHYSMEM_BITS - TB_SHIFT);
+ kaslr_regions[0].size_tb = calc_direct_mapping_size();
kaslr_regions[1].size_tb = VMALLOC_SIZE_TB;

- /*
- * 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 = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
- CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
-
- /* Adapt phyiscal memory region size based on available memory */
- if (memory_tb < kaslr_regions[0].size_tb)
- kaslr_regions[0].size_tb = memory_tb;

/*
* Calculate the vmemmap region size in TBs, aligned to a TB
--
2.20.1
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