1 // SPDX-License-Identifier: GPL-2.0
3  * This file implements KASLR memory randomization for x86_64. It randomizes
4  * the virtual address space of kernel memory regions (physical memory
11  * The physical memory mapping code was adapted to support P4D/PUD level
13  * 30,000 possible virtual addresses in average for each memory region.
14  * An additional low memory page is used to ensure each CPU can start with
17  * The order of each memory region is not changed. The feature looks at
20  * physical memory mapping is the available physical memory.
44  * Memory regions randomized by KASLR (except modules that use a separate logic
65 /* The end of the possible address space for physical memory */
68 /* Get size in bytes used by the memory region */
69 static inline unsigned long get_padding(struct kaslr_memory_region *region)  in get_padding()  argument
71 	return (region->size_tb << TB_SHIFT);  in get_padding()
74 /* Initialize base and padding for each memory region randomized with KASLR */
88 	 * These BUILD_BUG_ON checks ensure the memory layout is consistent  in kernel_randomize_memory()
96 	/* Preset the end of the possible address space for physical memory */  in kernel_randomize_memory()
97 	physmem_end = ((1ULL << MAX_PHYSMEM_BITS) - 1);  in kernel_randomize_memory()
101 	kaslr_regions[0].size_tb = 1 << (MAX_PHYSMEM_BITS - TB_SHIFT);  in kernel_randomize_memory()
105 	 * Update Physical memory mapping to available and  in kernel_randomize_memory()
106 	 * add padding if needed (especially for memory hotplug support).  in kernel_randomize_memory()
112 	/* Adapt physical memory region size based on available memory */  in kernel_randomize_memory()
117 	 * Calculate the vmemmap region size in TBs, aligned to a TB  in kernel_randomize_memory()
120 	vmemmap_size = (kaslr_regions[0].size_tb << (TB_SHIFT - PAGE_SHIFT)) *  in kernel_randomize_memory()
125 	remain_entropy = vaddr_end - vaddr_start;  in kernel_randomize_memory()
127 		remain_entropy -= get_padding(&kaslr_regions[i]);  in kernel_randomize_memory()
129 	prandom_seed_state(&rand_state, kaslr_get_random_long("Memory"));  in kernel_randomize_memory()
138 		entropy = remain_entropy / (ARRAY_SIZE(kaslr_regions) - i);  in kernel_randomize_memory()
144 		/* Calculate the end of the region */  in kernel_randomize_memory()
148 		 * direct-map. Update the physmem_end boundary.  in kernel_randomize_memory()
149 		 * No rounding required as the region starts  in kernel_randomize_memory()
153 			*kaslr_regions[i].end = __pa_nodebug(vaddr - 1);  in kernel_randomize_memory()
157 		remain_entropy -= entropy;  in kernel_randomize_memory()