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// SPDX-License-Identifier: GPL-2.0-only
// Copyright 2022 Google LLC
// Author: Ard Biesheuvel <ardb@google.com>
// NOTE: code in this file runs *very* early, and is not permitted to use
// global variables or anything that relies on absolute addressing.
#include <linux/libfdt.h>
#include <linux/init.h>
#include <linux/linkage.h>
#include <linux/types.h>
#include <linux/sizes.h>
#include <linux/string.h>
#include <asm/archrandom.h>
#include <asm/memory.h>
/* taken from lib/string.c */
static char *__strstr(const char *s1, const char *s2)
{
size_t l1, l2;
l2 = strlen(s2);
if (!l2)
return (char *)s1;
l1 = strlen(s1);
while (l1 >= l2) {
l1--;
if (!memcmp(s1, s2, l2))
return (char *)s1;
s1++;
}
return NULL;
}
static bool cmdline_contains_nokaslr(const u8 *cmdline)
{
const u8 *str;
str = __strstr(cmdline, "nokaslr");
return str == cmdline || (str > cmdline && *(str - 1) == ' ');
}
static bool is_kaslr_disabled_cmdline(void *fdt)
{
if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
int node;
const u8 *prop;
node = fdt_path_offset(fdt, "/chosen");
if (node < 0)
goto out;
prop = fdt_getprop(fdt, node, "bootargs", NULL);
if (!prop)
goto out;
if (cmdline_contains_nokaslr(prop))
return true;
if (IS_ENABLED(CONFIG_CMDLINE_EXTEND))
goto out;
return false;
}
out:
return cmdline_contains_nokaslr(CONFIG_CMDLINE);
}
static 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;
}
asmlinkage u64 kaslr_early_init(void *fdt)
{
u64 seed;
if (is_kaslr_disabled_cmdline(fdt))
return 0;
seed = get_kaslr_seed(fdt);
if (!seed) {
#ifdef CONFIG_ARCH_RANDOM
if (!__early_cpu_has_rndr() ||
!__arm64_rndr((unsigned long *)&seed))
#endif
return 0;
}
/*
* OK, so we are proceeding with KASLR enabled. Calculate a suitable
* kernel image offset from the seed. Let's place the kernel in the
* middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of
* the lower and upper quarters to avoid colliding with other
* allocations.
*/
return BIT(VA_BITS_MIN - 3) + (seed & GENMASK(VA_BITS_MIN - 3, 0));
}
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