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2023-12-11 072de836f53be56a70cecf70b43ae43b7ce17376 
 kernel/arch/arm64/kernel/kaslr.c
....@@ -1,9 +1,6 @@
1
+// SPDX-License-Identifier: GPL-2.0-only
12 /*
23  * Copyright (C) 2016 Linaro Ltd <ard.biesheuvel@linaro.org>
3
- *
4
- * This program is free software; you can redistribute it and/or modify
5
- * it under the terms of the GNU General Public License version 2 as
6
- * published by the Free Software Foundation.
74  */
85 
96 #include <linux/cache.h>
....@@ -13,15 +10,25 @@
1310 #include <linux/mm_types.h>
1411 #include <linux/sched.h>
1512 #include <linux/types.h>
13
+#include <linux/pgtable.h>
14
+#include <linux/random.h>
1615 
1716 #include <asm/cacheflush.h>
1817 #include <asm/fixmap.h>
1918 #include <asm/kernel-pgtable.h>
2019 #include <asm/memory.h>
2120 #include <asm/mmu.h>
22
-#include <asm/pgtable.h>
2321 #include <asm/sections.h>
22
+#include <asm/setup.h>
2423 
24
+enum kaslr_status {
25
+	KASLR_ENABLED,
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+	KASLR_DISABLED_CMDLINE,
27
+	KASLR_DISABLED_NO_SEED,
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+	KASLR_DISABLED_FDT_REMAP,
29
+};
30
+
31
+static enum kaslr_status __initdata kaslr_status;
2532 u64 __ro_after_init module_alloc_base;
2633 u16 __initdata memstart_offset_seed;
2734 
....@@ -44,26 +51,7 @@
4451 	return ret;
4552 }
4653 
47
-static __init const u8 *kaslr_get_cmdline(void *fdt)
48
-{
49
-	static __initconst const u8 default_cmdline[] = CONFIG_CMDLINE;
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-
51
-	if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
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-		int node;
53
-		const u8 *prop;
54
-
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-		node = fdt_path_offset(fdt, "/chosen");
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-		if (node < 0)
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-			goto out;
58
-
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-		prop = fdt_getprop(fdt, node, "bootargs", NULL);
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-		if (!prop)
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-			goto out;
62
-		return prop;
63
-	}
64
-out:
65
-	return default_cmdline;
66
-}
54
+struct arm64_ftr_override kaslr_feature_override __initdata;
6755 
6856 /*
6957  * This routine will be executed with the kernel mapped at its default virtual
....@@ -73,12 +61,11 @@
7361  * containing function pointers) to be reinitialized, and zero-initialized
7462  * .bss variables will be reset to 0.
7563  */
76
-u64 __init kaslr_early_init(u64 dt_phys)
64
+u64 __init kaslr_early_init(void)
7765 {
7866 	void *fdt;
7967 	u64 seed, offset, mask, module_range;
80
-	const u8 *cmdline, *str;
81
-	int size;
68
+	unsigned long raw;
8269 
8370 	/*
8471 	 * Set a reasonable default for module_alloc_base in case
....@@ -92,51 +79,66 @@
9279 	 * and proceed with KASLR disabled. We will make another
9380 	 * attempt at mapping the FDT in setup_machine()
9481 	 */
95
-	early_fixmap_init();
96
-	fdt = fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL);
97
-	if (!fdt)
82
+	fdt = get_early_fdt_ptr();
83
+	if (!fdt) {
84
+		kaslr_status = KASLR_DISABLED_FDT_REMAP;
9885 		return 0;
86
+	}
9987 
10088 	/*
10189 	 * Retrieve (and wipe) the seed from the FDT
10290 	 */
10391 	seed = get_kaslr_seed(fdt);
104
-	if (!seed)
105
-		return 0;
10692 
10793 	/*
10894 	 * Check if 'nokaslr' appears on the command line, and
10995 	 * return 0 if that is the case.
11096 	 */
111
-	cmdline = kaslr_get_cmdline(fdt);
112
-	str = strstr(cmdline, "nokaslr");
113
-	if (str == cmdline || (str > cmdline && *(str - 1) == ' '))
97
+	if (kaslr_feature_override.val & kaslr_feature_override.mask & 0xf) {
98
+		kaslr_status = KASLR_DISABLED_CMDLINE;
11499 		return 0;
100
+	}
101
+
102
+	/*
103
+	 * Mix in any entropy obtainable architecturally if enabled
104
+	 * and supported.
105
+	 */
106
+
107
+	if (arch_get_random_seed_long_early(&raw))
108
+		seed ^= raw;
109
+
110
+	if (!seed) {
111
+		kaslr_status = KASLR_DISABLED_NO_SEED;
112
+		return 0;
113
+	}
115114 
116115 	/*
117116 	 * OK, so we are proceeding with KASLR enabled. Calculate a suitable
118117 	 * kernel image offset from the seed. Let's place the kernel in the
119
-	 * middle half of the VMALLOC area (VA_BITS - 2), and stay clear of
118
+	 * middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of
120119 	 * the lower and upper quarters to avoid colliding with other
121120 	 * allocations.
122121 	 * Even if we could randomize at page granularity for 16k and 64k pages,
123122 	 * let's always round to 2 MB so we don't interfere with the ability to
124123 	 * map using contiguous PTEs
125124 	 */
126
-	mask = ((1UL << (VA_BITS - 2)) - 1) & ~(SZ_2M - 1);
127
-	offset = BIT(VA_BITS - 3) + (seed & mask);
125
+	mask = ((1UL << (VA_BITS_MIN - 2)) - 1) & ~(SZ_2M - 1);
126
+	offset = BIT(VA_BITS_MIN - 3) + (seed & mask);
128127 
129128 	/* use the top 16 bits to randomize the linear region */
130129 	memstart_offset_seed = seed >> 48;
131130 
132
-	if (IS_ENABLED(CONFIG_KASAN))
131
+	if (!IS_ENABLED(CONFIG_KASAN_VMALLOC) &&
132
+	    (IS_ENABLED(CONFIG_KASAN_GENERIC) ||
133
+	     IS_ENABLED(CONFIG_KASAN_SW_TAGS)))
133134 		/*
134
-		 * KASAN does not expect the module region to intersect the
135
-		 * vmalloc region, since shadow memory is allocated for each
136
-		 * module at load time, whereas the vmalloc region is shadowed
137
-		 * by KASAN zero pages. So keep modules out of the vmalloc
138
-		 * region if KASAN is enabled, and put the kernel well within
139
-		 * 4 GB of the module region.
135
+		 * KASAN without KASAN_VMALLOC does not expect the module region
136
+		 * to intersect the vmalloc region, since shadow memory is
137
+		 * allocated for each module at load time, whereas the vmalloc
138
+		 * region is shadowed by KASAN zero pages. So keep modules
139
+		 * out of the vmalloc region if KASAN is enabled without
140
+		 * KASAN_VMALLOC, and put the kernel well within 4 GB of the
141
+		 * module region.
140142 		 */
141143 		return offset % SZ_2G;
142144 
....@@ -173,3 +175,24 @@
173175 
174176 	return offset;
175177 }
178
+
179
+static int __init kaslr_init(void)
180
+{
181
+	switch (kaslr_status) {
182
+	case KASLR_ENABLED:
183
+		pr_info("KASLR enabled\n");
184
+		break;
185
+	case KASLR_DISABLED_CMDLINE:
186
+		pr_info("KASLR disabled on command line\n");
187
+		break;
188
+	case KASLR_DISABLED_NO_SEED:
189
+		pr_warn("KASLR disabled due to lack of seed\n");
190
+		break;
191
+	case KASLR_DISABLED_FDT_REMAP:
192
+		pr_warn("KASLR disabled due to FDT remapping failure\n");
193
+		break;
194
+	}
195
+
196
+	return 0;
197
+}
198
+core_initcall(kaslr_init)