// SPDX-License-Identifier: GPL-2.0-only
//
// Copyright (C) 2019 Jason Yan <[email protected]>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/stddef.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/memblock.h>
#include <linux/libfdt.h>
#include <linux/crash_reserve.h>
#include <linux/of.h>
#include <linux/of_fdt.h>
#include <asm/cacheflush.h>
#include <asm/kdump.h>
#include <mm/mmu_decl.h>
struct regions {
unsigned long pa_start;
unsigned long pa_end;
unsigned long kernel_size;
unsigned long dtb_start;
unsigned long dtb_end;
unsigned long initrd_start;
unsigned long initrd_end;
unsigned long crash_start;
unsigned long crash_end;
int reserved_mem;
int reserved_mem_addr_cells;
int reserved_mem_size_cells;
};
struct regions __initdata regions;
static __init void kaslr_get_cmdline(void *fdt)
{
early_init_dt_scan_chosen(boot_command_line);
}
static unsigned long __init rotate_xor(unsigned long hash, const void *area,
size_t size)
{
size_t i;
const unsigned long *ptr = area;
for (i = 0; i < size / sizeof(hash); i++) {
/* Rotate by odd number of bits and XOR. */
hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
hash ^= ptr[i];
}
return hash;
}
/* Attempt to create a simple starting entropy. This can make it defferent for
* every build but it is still not enough. Stronger entropy should
* be added to make it change for every boot.
*/
static unsigned long __init get_boot_seed(void *fdt)
{
unsigned long hash = 0;
/* build-specific string for starting entropy. */
hash = rotate_xor(hash, linux_banner, strlen(linux_banner));
hash = rotate_xor(hash, fdt, fdt_totalsize(fdt));
return hash;
}
static __init u64 get_kaslr_seed(void *fdt)
{
int node, len;
fdt64_t *prop;
u64 ret;
node = fdt_path_offset(fdt, "/chosen");
if (node < 0)
return 0;
prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len);
if (!prop || len != sizeof(u64))
return 0;
ret = fdt64_to_cpu(*prop);
*prop = 0;
return ret;
}
static __init bool regions_overlap(u32 s1, u32 e1, u32 s2, u32 e2)
{
return e1 >= s2 && e2 >= s1;
}
static __init bool overlaps_reserved_region(const void *fdt, u32 start,
u32 end)
{
int subnode, len, i;
u64 base, size;
/* check for overlap with /memreserve/ entries */
for (i = 0; i < fdt_num_mem_rsv(fdt); i++) {
if (fdt_get_mem_rsv(fdt, i, &base, &size) < 0)
continue;
if (regions_overlap(start, end, base, base + size))
return true;
}
if (regions.reserved_mem < 0)
return false;
/* check for overlap with static reservations in /reserved-memory */
for (subnode = fdt_first_subnode(fdt, regions.reserved_mem);
subnode >= 0;
subnode = fdt_next_subnode(fdt, subnode)) {
const fdt32_t *reg;
u64 rsv_end;
len = 0;
reg = fdt_getprop(fdt, subnode, "reg", &len);
while (len >= (regions.reserved_mem_addr_cells +
regions.reserved_mem_size_cells)) {
base = fdt32_to_cpu(reg[0]);
if (regions.reserved_mem_addr_cells == 2)
base = (base << 32) | fdt32_to_cpu(reg[1]);
reg += regions.reserved_mem_addr_cells;
len -= 4 * regions.reserved_mem_addr_cells;
size = fdt32_to_cpu(reg[0]);
if (regions.reserved_mem_size_cells == 2)
size = (size << 32) | fdt32_to_cpu(reg[1]);
reg += regions.reserved_mem_size_cells;
len -= 4 * regions.reserved_mem_size_cells;
if (base >= regions.pa_end)
continue;
rsv_end = min(base + size, (u64)U32_MAX);
if (regions_overlap(start, end, base, rsv_end))
return true;
}
}
return false;
}
static __init bool overlaps_region(const void *fdt, u32 start,
u32 end)
{
if (regions_overlap(start, end, __pa(_stext), __pa(_end)))
return true;
if (regions_overlap(start, end, regions.dtb_start,
regions.dtb_end))
return true;
if (regions_overlap(start, end, regions.initrd_start,
regions.initrd_end))
return true;
if (regions_overlap(start, end, regions.crash_start,
regions.crash_end))
return true;
return overlaps_reserved_region(fdt, start, end);
}
static void __init get_crash_kernel(void *fdt, unsigned long size)
{
#ifdef CONFIG_CRASH_RESERVE
unsigned long long crash_size, crash_base;
int ret;
ret = parse_crashkernel(boot_command_line, size, &crash_size,
&crash_base, NULL, NULL);
if (ret != 0 || crash_size == 0)
return;
if (crash_base == 0)
crash_base = KDUMP_KERNELBASE;
regions.crash_start = (unsigned long)crash_base;
regions.crash_end = (unsigned long)(crash_base + crash_size);
pr_debug("crash_base=0x%llx crash_size=0x%llx\n", crash_base, crash_size);
#endif
}
static void __init get_initrd_range(void *fdt)
{
u64 start, end;
int node, len;
const __be32 *prop;
node = fdt_path_offset(fdt, "/chosen");
if (node < 0)
return;
prop = fdt_getprop(fdt, node, "linux,initrd-start", &len);
if (!prop)
return;
start = of_read_number(prop, len / 4);
prop = fdt_getprop(fdt, node, "linux,initrd-end", &len);
if (!prop)
return;
end = of_read_number(prop, len / 4);
regions.initrd_start = (unsigned long)start;
regions.initrd_end = (unsigned long)end;
pr_debug("initrd_start=0x%llx initrd_end=0x%llx\n", start, end);
}
static __init unsigned long get_usable_address(const void *fdt,
unsigned long start,
unsigned long offset)
{
unsigned long pa;
unsigned long pa_end;
for (pa = offset; (long)pa > (long)start; pa -= SZ_16K) {
pa_end = pa + regions.kernel_size;
if (overlaps_region(fdt, pa, pa_end))
continue;
return pa;
}
return 0;
}
static __init void get_cell_sizes(const void *fdt, int node, int *addr_cells,
int *size_cells)
{
const int *prop;
int len;
/*
* Retrieve the #address-cells and #size-cells properties
* from the 'node', or use the default if not provided.
*/
*addr_cells = *size_cells = 1;
prop = fdt_getprop(fdt, node, "#address-cells", &len);
if (len == 4)
*addr_cells = fdt32_to_cpu(*prop);
prop = fdt_getprop(fdt, node, "#size-cells", &len);
if (len == 4)
*size_cells = fdt32_to_cpu(*prop);
}
static unsigned long __init kaslr_legal_offset(void *dt_ptr, unsigned long index,
unsigned long offset)
{
unsigned long koffset = 0;
unsigned long start;
while ((long)index >= 0) {
offset = memstart_addr + index * SZ_64M + offset;
start = memstart_addr + index * SZ_64M;
koffset = get_usable_address(dt_ptr, start, offset);
if (koffset)
break;
index--;
}
if (koffset != 0)
koffset -= memstart_addr;
return koffset;
}
static inline __init bool kaslr_disabled(void)
{
return strstr(boot_command_line, "nokaslr") != NULL;
}
static unsigned long __init kaslr_choose_location(void *dt_ptr, phys_addr_t size,
unsigned long kernel_sz)
{
unsigned long offset, random;
unsigned long ram, linear_sz;
u64 seed;
unsigned long index;
kaslr_get_cmdline(dt_ptr);
if (kaslr_disabled())
return 0;
random = get_boot_seed(dt_ptr);
seed = get_tb() << 32;
seed ^= get_tb();
random = rotate_xor(random, &seed, sizeof(seed));
/*
* Retrieve (and wipe) the seed from the FDT
*/
seed = get_kaslr_seed(dt_ptr);
if (seed)
random = rotate_xor(random, &seed, sizeof(seed));
else
pr_warn("KASLR: No safe seed for randomizing the kernel base.\n");
ram = min_t(phys_addr_t, __max_low_memory, size);
ram = map_mem_in_cams(ram, CONFIG_LOWMEM_CAM_NUM, true, true);
linear_sz = min_t(unsigned long, ram, SZ_512M);
/* If the linear size is smaller than 64M, do not randomize */
if (linear_sz < SZ_64M)
return 0;
/* check for a reserved-memory node and record its cell sizes */
regions.reserved_mem = fdt_path_offset(dt_ptr, "/reserved-memory");
if (regions.reserved_mem >= 0)
get_cell_sizes(dt_ptr, regions.reserved_mem,
®ions.reserved_mem_addr_cells,
®ions.reserved_mem_size_cells);
regions.pa_start = memstart_addr;
regions.pa_end = memstart_addr + linear_sz;
regions.dtb_start = __pa(dt_ptr);
regions.dtb_end = __pa(dt_ptr) + fdt_totalsize(dt_ptr);
regions.kernel_size = kernel_sz;
get_initrd_range(dt_ptr);
get_crash_kernel(dt_ptr, ram);
/*
* Decide which 64M we want to start
* Only use the low 8 bits of the random seed
*/
index = random & 0xFF;
index %= linear_sz / SZ_64M;
/* Decide offset inside 64M */
offset = random % (SZ_64M - kernel_sz);
offset = round_down(offset, SZ_16K);
return kaslr_legal_offset(dt_ptr, index, offset);
}
/*
* To see if we need to relocate the kernel to a random offset
* void *dt_ptr - address of the device tree
* phys_addr_t size - size of the first memory block
*/
notrace void __init kaslr_early_init(void *dt_ptr, phys_addr_t size)
{
unsigned long tlb_virt;
phys_addr_t tlb_phys;
unsigned long offset;
unsigned long kernel_sz;
kernel_sz = (unsigned long)_end - (unsigned long)_stext;
offset = kaslr_choose_location(dt_ptr, size, kernel_sz);
if (offset == 0)
return;
kernstart_virt_addr += offset;
kernstart_addr += offset;
is_second_reloc = 1;
if (offset >= SZ_64M) {
tlb_virt = round_down(kernstart_virt_addr, SZ_64M);
tlb_phys = round_down(kernstart_addr, SZ_64M);
/* Create kernel map to relocate in */
create_kaslr_tlb_entry(1, tlb_virt, tlb_phys);
}
/* Copy the kernel to its new location and run */
memcpy((void *)kernstart_virt_addr, (void *)_stext, kernel_sz);
flush_icache_range(kernstart_virt_addr, kernstart_virt_addr + kernel_sz);
reloc_kernel_entry(dt_ptr, kernstart_virt_addr);
}
void __init kaslr_late_init(void)
{
/* If randomized, clear the original kernel */
if (kernstart_virt_addr != KERNELBASE) {
unsigned long kernel_sz;
kernel_sz = (unsigned long)_end - kernstart_virt_addr;
memzero_explicit((void *)KERNELBASE, kernel_sz);
}
}
Codebase Browser
linux