195 lines
6.2 KiB
C
195 lines
6.2 KiB
C
|
/*
|
||
|
|
* This file implements KASLR memory randomization for x86_64. It randomizes
|
||
|
|
* the virtual address space of kernel memory regions (physical memory
|
||
|
|
* mapping, vmalloc & vmemmap) for x86_64. This security feature mitigates
|
||
|
|
* exploits relying on predictable kernel addresses.
|
||
|
|
*
|
||
|
|
* Entropy is generated using the KASLR early boot functions now shared in
|
||
|
|
* the lib directory (originally written by Kees Cook). Randomization is
|
||
|
|
* done on PGD & PUD page table levels to increase possible addresses. The
|
||
|
|
* physical memory mapping code was adapted to support PUD level virtual
|
||
|
|
* addresses. This implementation on the best configuration provides 30,000
|
||
|
|
* possible virtual addresses in average for each memory region. An additional
|
||
|
|
* low memory page is used to ensure each CPU can start with a PGD aligned
|
||
|
|
* virtual address (for realmode).
|
||
|
|
*
|
||
|
|
* The order of each memory region is not changed. The feature looks at
|
||
|
|
* the available space for the regions based on different configuration
|
||
|
|
* options and randomizes the base and space between each. The size of the
|
||
|
|
* physical memory mapping is the available physical memory.
|
||
|
|
*/
|
||
|
|
|
||
|
|
#include <linux/kernel.h>
|
||
|
|
#include <linux/init.h>
|
||
|
|
#include <linux/random.h>
|
||
|
|
|
||
|
|
#include <asm/pgalloc.h>
|
||
|
|
#include <asm/pgtable.h>
|
||
|
|
#include <asm/setup.h>
|
||
|
|
#include <asm/kaslr.h>
|
||
|
|
|
||
|
|
#include "mm_internal.h"
|
||
|
|
|
||
|
|
#define TB_SHIFT 40
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Virtual address start and end range for randomization. The end changes base
|
||
|
|
* on configuration to have the highest amount of space for randomization.
|
||
|
|
* It increases the possible random position for each randomized region.
|
||
|
|
*
|
||
|
|
* You need to add an if/def entry if you introduce a new memory region
|
||
|
|
* compatible with KASLR. Your entry must be in logical order with memory
|
||
|
|
* layout. For example, ESPFIX is before EFI because its virtual address is
|
||
|
|
* before. You also need to add a BUILD_BUG_ON() in kernel_randomize_memory() to
|
||
|
|
* ensure that this order is correct and won't be changed.
|
||
|
|
*/
|
||
|
|
static const unsigned long vaddr_start = __PAGE_OFFSET_BASE;
|
||
|
|
|
||
|
|
#if defined(CONFIG_X86_ESPFIX64)
|
||
|
|
static const unsigned long vaddr_end = ESPFIX_BASE_ADDR;
|
||
|
|
#elif defined(CONFIG_EFI)
|
||
|
|
static const unsigned long vaddr_end = EFI_VA_END;
|
||
|
|
#else
|
||
|
|
static const unsigned long vaddr_end = __START_KERNEL_map;
|
||
|
|
#endif
|
||
|
|
|
||
|
|
/* Default values */
|
||
|
|
unsigned long page_offset_base = __PAGE_OFFSET_BASE;
|
||
|
|
EXPORT_SYMBOL(page_offset_base);
|
||
|
|
unsigned long vmalloc_base = __VMALLOC_BASE;
|
||
|
|
EXPORT_SYMBOL(vmalloc_base);
|
||
|
|
unsigned long vmemmap_base = __VMEMMAP_BASE;
|
||
|
|
EXPORT_SYMBOL(vmemmap_base);
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Memory regions randomized by KASLR (except modules that use a separate logic
|
||
|
|
* earlier during boot). The list is ordered based on virtual addresses. This
|
||
|
|
* order is kept after randomization.
|
||
|
|
*/
|
||
|
|
static __initdata struct kaslr_memory_region {
|
||
|
|
unsigned long *base;
|
||
|
|
unsigned long size_tb;
|
||
|
|
} kaslr_regions[] = {
|
||
|
|
{ &page_offset_base, 64/* Maximum */ },
|
||
|
|
{ &vmalloc_base, VMALLOC_SIZE_TB },
|
||
|
|
{ &vmemmap_base, 1 },
|
||
|
|
};
|
||
|
|
|
||
|
|
/* Get size in bytes used by the memory region */
|
||
|
|
static inline unsigned long get_padding(struct kaslr_memory_region *region)
|
||
|
|
{
|
||
|
|
return (region->size_tb << TB_SHIFT);
|
||
|
|
}
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Apply no randomization if KASLR was disabled at boot or if KASAN
|
||
|
|
* is enabled. KASAN shadow mappings rely on regions being PGD aligned.
|
||
|
|
*/
|
||
|
|
static inline bool kaslr_memory_enabled(void)
|
||
|
|
{
|
||
|
|
return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
|
||
|
|
}
|
||
|
|
|
||
|
|
/* Initialize base and padding for each memory region randomized with KASLR */
|
||
|
|
void __init kernel_randomize_memory(void)
|
||
|
|
{
|
||
|
|
size_t i;
|
||
|
|
unsigned long vaddr = vaddr_start;
|
||
|
|
unsigned long rand, memory_tb;
|
||
|
|
struct rnd_state rand_state;
|
||
|
|
unsigned long remain_entropy;
|
||
|
|
|
||
|
|
/*
|
||
|
|
* All these BUILD_BUG_ON checks ensures the memory layout is
|
||
|
|
* consistent with the vaddr_start/vaddr_end variables.
|
||
|
|
*/
|
||
|
|
BUILD_BUG_ON(vaddr_start >= vaddr_end);
|
||
|
|
BUILD_BUG_ON(IS_ENABLED(CONFIG_X86_ESPFIX64) &&
|
||
|
|
vaddr_end >= EFI_VA_END);
|
||
|
|
BUILD_BUG_ON((IS_ENABLED(CONFIG_X86_ESPFIX64) ||
|
||
|
|
IS_ENABLED(CONFIG_EFI)) &&
|
||
|
|
vaddr_end >= __START_KERNEL_map);
|
||
|
|
BUILD_BUG_ON(vaddr_end > __START_KERNEL_map);
|
||
|
|
|
||
|
|
if (!kaslr_memory_enabled())
|
||
|
|
return;
|
||
|
|
|
||
|
|
/*
|
||
|
|
* 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 entropy available between regions */
|
||
|
|
remain_entropy = vaddr_end - vaddr_start;
|
||
|
|
for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)
|
||
|
|
remain_entropy -= get_padding(&kaslr_regions[i]);
|
||
|
|
|
||
|
|
prandom_seed_state(&rand_state, kaslr_get_random_long("Memory"));
|
||
|
|
|
||
|
|
for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++) {
|
||
|
|
unsigned long entropy;
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Select a random virtual address using the extra entropy
|
||
|
|
* available.
|
||
|
|
*/
|
||
|
|
entropy = remain_entropy / (ARRAY_SIZE(kaslr_regions) - i);
|
||
|
|
prandom_bytes_state(&rand_state, &rand, sizeof(rand));
|
||
|
|
entropy = (rand % (entropy + 1)) & PUD_MASK;
|
||
|
|
vaddr += entropy;
|
||
|
|
*kaslr_regions[i].base = vaddr;
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Jump the region and add a minimum padding based on
|
||
|
|
* randomization alignment.
|
||
|
|
*/
|
||
|
|
vaddr += get_padding(&kaslr_regions[i]);
|
||
|
|
vaddr = round_up(vaddr + 1, PUD_SIZE);
|
||
|
|
remain_entropy -= entropy;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Create PGD aligned trampoline table to allow real mode initialization
|
||
|
|
* of additional CPUs. Consume only 1 low memory page.
|
||
|
|
*/
|
||
|
|
void __meminit init_trampoline(void)
|
||
|
|
{
|
||
|
|
unsigned long paddr, paddr_next;
|
||
|
|
pgd_t *pgd;
|
||
|
|
pud_t *pud_page, *pud_page_tramp;
|
||
|
|
int i;
|
||
|
|
|
||
|
|
if (!kaslr_memory_enabled()) {
|
||
|
|
init_trampoline_default();
|
||
|
|
return;
|
||
|
|
}
|
||
|
|
|
||
|
|
pud_page_tramp = alloc_low_page();
|
||
|
|
|
||
|
|
paddr = 0;
|
||
|
|
pgd = pgd_offset_k((unsigned long)__va(paddr));
|
||
|
|
pud_page = (pud_t *) pgd_page_vaddr(*pgd);
|
||
|
|
|
||
|
|
for (i = pud_index(paddr); i < PTRS_PER_PUD; i++, paddr = paddr_next) {
|
||
|
|
pud_t *pud, *pud_tramp;
|
||
|
|
unsigned long vaddr = (unsigned long)__va(paddr);
|
||
|
|
|
||
|
|
pud_tramp = pud_page_tramp + pud_index(paddr);
|
||
|
|
pud = pud_page + pud_index(vaddr);
|
||
|
|
paddr_next = (paddr & PUD_MASK) + PUD_SIZE;
|
||
|
|
|
||
|
|
*pud_tramp = *pud;
|
||
|
|
}
|
||
|
|
|
||
|
|
/* Avoid set_pgd(), in case it's complicated by CONFIG_PAGE_TABLE_ISOLATION */
|
||
|
|
trampoline_pgd_entry = __pgd(_KERNPG_TABLE | __pa(pud_page_tramp));
|
||
|
|
}
|