1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Early cpufeature override framework
4 *
5 * Copyright (C) 2020 Google LLC
6 * Author: Marc Zyngier <maz@kernel.org>
7 */
8
9 #include <linux/ctype.h>
10 #include <linux/kernel.h>
11 #include <linux/libfdt.h>
12
13 #include <asm/cacheflush.h>
14 #include <asm/cpufeature.h>
15 #include <asm/setup.h>
16
17 #define FTR_DESC_NAME_LEN 20
18 #define FTR_DESC_FIELD_LEN 10
19 #define FTR_ALIAS_NAME_LEN 30
20 #define FTR_ALIAS_OPTION_LEN 80
21
22 struct ftr_set_desc {
23 char name[FTR_DESC_NAME_LEN];
24 struct arm64_ftr_override *override;
25 struct {
26 char name[FTR_DESC_FIELD_LEN];
27 u8 shift;
28 bool (*filter)(u64 val);
29 } fields[];
30 };
31
mmfr1_vh_filter(u64 val)32 static bool __init mmfr1_vh_filter(u64 val)
33 {
34 /*
35 * If we ever reach this point while running VHE, we're
36 * guaranteed to be on one of these funky, VHE-stuck CPUs. If
37 * the user was trying to force nVHE on us, proceed with
38 * attitude adjustment.
39 */
40 return !(is_kernel_in_hyp_mode() && val == 0);
41 }
42
43 static const struct ftr_set_desc mmfr1 __initconst = {
44 .name = "id_aa64mmfr1",
45 .override = &id_aa64mmfr1_override,
46 .fields = {
47 { "vh", ID_AA64MMFR1_VHE_SHIFT, mmfr1_vh_filter },
48 {}
49 },
50 };
51
52 static const struct ftr_set_desc pfr1 __initconst = {
53 .name = "id_aa64pfr1",
54 .override = &id_aa64pfr1_override,
55 .fields = {
56 { "bt", ID_AA64PFR1_BT_SHIFT },
57 { "mte", ID_AA64PFR1_MTE_SHIFT},
58 {}
59 },
60 };
61
62 static const struct ftr_set_desc isar1 __initconst = {
63 .name = "id_aa64isar1",
64 .override = &id_aa64isar1_override,
65 .fields = {
66 { "gpi", ID_AA64ISAR1_GPI_SHIFT },
67 { "gpa", ID_AA64ISAR1_GPA_SHIFT },
68 { "api", ID_AA64ISAR1_API_SHIFT },
69 { "apa", ID_AA64ISAR1_APA_SHIFT },
70 {}
71 },
72 };
73
74 extern struct arm64_ftr_override kaslr_feature_override;
75
76 static const struct ftr_set_desc kaslr __initconst = {
77 .name = "kaslr",
78 #ifdef CONFIG_RANDOMIZE_BASE
79 .override = &kaslr_feature_override,
80 #endif
81 .fields = {
82 { "disabled", 0 },
83 {}
84 },
85 };
86
87 static const struct ftr_set_desc * const regs[] __initconst = {
88 &mmfr1,
89 &pfr1,
90 &isar1,
91 &kaslr,
92 };
93
94 static const struct {
95 char alias[FTR_ALIAS_NAME_LEN];
96 char feature[FTR_ALIAS_OPTION_LEN];
97 } aliases[] __initconst = {
98 { "kvm-arm.mode=nvhe", "id_aa64mmfr1.vh=0" },
99 { "kvm-arm.mode=protected", "id_aa64mmfr1.vh=0" },
100 { "arm64.nobti", "id_aa64pfr1.bt=0" },
101 { "arm64.nopauth",
102 "id_aa64isar1.gpi=0 id_aa64isar1.gpa=0 "
103 "id_aa64isar1.api=0 id_aa64isar1.apa=0" },
104 { "arm64.nomte", "id_aa64pfr1.mte=0" },
105 { "nokaslr", "kaslr.disabled=1" },
106 };
107
find_field(const char * cmdline,const struct ftr_set_desc * reg,int f,u64 * v)108 static int __init find_field(const char *cmdline,
109 const struct ftr_set_desc *reg, int f, u64 *v)
110 {
111 char opt[FTR_DESC_NAME_LEN + FTR_DESC_FIELD_LEN + 2];
112 int len;
113
114 len = snprintf(opt, ARRAY_SIZE(opt), "%s.%s=",
115 reg->name, reg->fields[f].name);
116
117 if (!parameqn(cmdline, opt, len))
118 return -1;
119
120 return kstrtou64(cmdline + len, 0, v);
121 }
122
match_options(const char * cmdline)123 static void __init match_options(const char *cmdline)
124 {
125 int i;
126
127 for (i = 0; i < ARRAY_SIZE(regs); i++) {
128 int f;
129
130 if (!regs[i]->override)
131 continue;
132
133 for (f = 0; strlen(regs[i]->fields[f].name); f++) {
134 u64 shift = regs[i]->fields[f].shift;
135 u64 mask = 0xfUL << shift;
136 u64 v;
137
138 if (find_field(cmdline, regs[i], f, &v))
139 continue;
140
141 /*
142 * If an override gets filtered out, advertise
143 * it by setting the value to 0xf, but
144 * clearing the mask... Yes, this is fragile.
145 */
146 if (regs[i]->fields[f].filter &&
147 !regs[i]->fields[f].filter(v)) {
148 regs[i]->override->val |= mask;
149 regs[i]->override->mask &= ~mask;
150 continue;
151 }
152
153 regs[i]->override->val &= ~mask;
154 regs[i]->override->val |= (v << shift) & mask;
155 regs[i]->override->mask |= mask;
156
157 return;
158 }
159 }
160 }
161
__parse_cmdline(const char * cmdline,bool parse_aliases)162 static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
163 {
164 do {
165 char buf[256];
166 size_t len;
167 int i;
168
169 cmdline = skip_spaces(cmdline);
170
171 for (len = 0; cmdline[len] && !isspace(cmdline[len]); len++);
172 if (!len)
173 return;
174
175 len = min(len, ARRAY_SIZE(buf) - 1);
176 strncpy(buf, cmdline, len);
177 buf[len] = 0;
178
179 if (strcmp(buf, "--") == 0)
180 return;
181
182 cmdline += len;
183
184 match_options(buf);
185
186 for (i = 0; parse_aliases && i < ARRAY_SIZE(aliases); i++)
187 if (parameq(buf, aliases[i].alias))
188 __parse_cmdline(aliases[i].feature, false);
189 } while (1);
190 }
191
get_bootargs_cmdline(void)192 static __init const u8 *get_bootargs_cmdline(void)
193 {
194 const u8 *prop;
195 void *fdt;
196 int node;
197
198 fdt = get_early_fdt_ptr();
199 if (!fdt)
200 return NULL;
201
202 node = fdt_path_offset(fdt, "/chosen");
203 if (node < 0)
204 return NULL;
205
206 prop = fdt_getprop(fdt, node, "bootargs", NULL);
207 if (!prop)
208 return NULL;
209
210 return strlen(prop) ? prop : NULL;
211 }
212
parse_cmdline(void)213 static __init void parse_cmdline(void)
214 {
215 const u8 *prop = get_bootargs_cmdline();
216
217 if (IS_ENABLED(CONFIG_CMDLINE_EXTEND) ||
218 IS_ENABLED(CONFIG_CMDLINE_FORCE) ||
219 !prop) {
220 __parse_cmdline(CONFIG_CMDLINE, true);
221 }
222
223 if (!IS_ENABLED(CONFIG_CMDLINE_FORCE) && prop)
224 __parse_cmdline(prop, true);
225 }
226
227 /* Keep checkers quiet */
228 void init_feature_override(void);
229
init_feature_override(void)230 asmlinkage void __init init_feature_override(void)
231 {
232 int i;
233
234 for (i = 0; i < ARRAY_SIZE(regs); i++) {
235 if (regs[i]->override) {
236 regs[i]->override->val = 0;
237 regs[i]->override->mask = 0;
238 }
239 }
240
241 parse_cmdline();
242
243 for (i = 0; i < ARRAY_SIZE(regs); i++) {
244 if (regs[i]->override)
245 dcache_clean_inval_poc((unsigned long)regs[i]->override,
246 (unsigned long)regs[i]->override +
247 sizeof(*regs[i]->override));
248 }
249 }
250