Messages in this thread Patch in this message | | | From | Masayoshi Mizuma <> | Subject | [PATCH v6 4/4] x86/mm/KASLR: Adjust the padding size for the direct mapping. | Date | Fri, 6 Dec 2019 11:57:07 -0500 |
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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.
Acked-by: Baoquan He <bhe@redhat.com> Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com> --- arch/x86/mm/kaslr.c | 63 ++++++++++++++++++++++++++++++++++----------- 1 file changed, 48 insertions(+), 15 deletions(-)
diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c index dc6182eecefa..b3f2f468d20f 100644 --- a/arch/x86/mm/kaslr.c +++ b/arch/x86/mm/kaslr.c @@ -70,15 +70,58 @@ 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. + * + * And in case CONFIG_MEMORY_HOTPLUG is enabled and boot_params.max_addr + * has a physical memory address, that means the system memory can be + * expanded by memory hot-add to boot_params.max_addr. Set the size + * of direct mapping area to boot_params.max_addr so that we can avoid + * overwriting the hot-added memory. + */ +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 +138,10 @@ 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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