111 lines
2.3 KiB
C
111 lines
2.3 KiB
C
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// SPDX-License-Identifier: GPL-2.0-only
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// Copyright 2022 Google LLC
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// Author: Ard Biesheuvel <ardb@google.com>
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// NOTE: code in this file runs *very* early, and is not permitted to use
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// global variables or anything that relies on absolute addressing.
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#include <linux/libfdt.h>
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#include <linux/init.h>
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#include <linux/linkage.h>
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#include <linux/types.h>
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#include <linux/sizes.h>
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#include <linux/string.h>
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#include <asm/archrandom.h>
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#include <asm/memory.h>
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/* taken from lib/string.c */
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static char *__strstr(const char *s1, const char *s2)
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{
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size_t l1, l2;
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l2 = strlen(s2);
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if (!l2)
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return (char *)s1;
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l1 = strlen(s1);
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while (l1 >= l2) {
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l1--;
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if (!memcmp(s1, s2, l2))
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return (char *)s1;
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s1++;
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}
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return NULL;
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}
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static bool cmdline_contains_nokaslr(const u8 *cmdline)
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{
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const u8 *str;
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str = __strstr(cmdline, "nokaslr");
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return str == cmdline || (str > cmdline && *(str - 1) == ' ');
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}
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static bool is_kaslr_disabled_cmdline(void *fdt)
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{
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if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
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int node;
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const u8 *prop;
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node = fdt_path_offset(fdt, "/chosen");
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if (node < 0)
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goto out;
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prop = fdt_getprop(fdt, node, "bootargs", NULL);
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if (!prop)
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goto out;
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if (cmdline_contains_nokaslr(prop))
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return true;
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if (IS_ENABLED(CONFIG_CMDLINE_EXTEND))
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goto out;
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return false;
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}
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out:
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return cmdline_contains_nokaslr(CONFIG_CMDLINE);
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}
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static u64 get_kaslr_seed(void *fdt)
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{
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int node, len;
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fdt64_t *prop;
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u64 ret;
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node = fdt_path_offset(fdt, "/chosen");
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if (node < 0)
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return 0;
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prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len);
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if (!prop || len != sizeof(u64))
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return 0;
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ret = fdt64_to_cpu(*prop);
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*prop = 0;
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return ret;
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}
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asmlinkage u64 kaslr_early_init(void *fdt)
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{
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u64 seed;
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if (is_kaslr_disabled_cmdline(fdt))
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return 0;
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seed = get_kaslr_seed(fdt);
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if (!seed) {
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if (!__early_cpu_has_rndr() ||
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!__arm64_rndr((unsigned long *)&seed))
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return 0;
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}
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/*
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* OK, so we are proceeding with KASLR enabled. Calculate a suitable
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* kernel image offset from the seed. Let's place the kernel in the
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* middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of
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* the lower and upper quarters to avoid colliding with other
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* allocations.
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*/
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return BIT(VA_BITS_MIN - 3) + (seed & GENMASK(VA_BITS_MIN - 3, 0));
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}
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