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 {}
58 },
59 };
60
61 static const struct ftr_set_desc isar1 __initconst = {
62 .name = "id_aa64isar1",
63 .override = &id_aa64isar1_override,
64 .fields = {
65 { "gpi", ID_AA64ISAR1_GPI_SHIFT },
66 { "gpa", ID_AA64ISAR1_GPA_SHIFT },
67 { "api", ID_AA64ISAR1_API_SHIFT },
68 { "apa", ID_AA64ISAR1_APA_SHIFT },
69 {}
70 },
71 };
72
73 extern struct arm64_ftr_override kaslr_feature_override;
74
75 static const struct ftr_set_desc kaslr __initconst = {
76 .name = "kaslr",
77 #ifdef CONFIG_RANDOMIZE_BASE
78 .override = &kaslr_feature_override,
79 #endif
80 .fields = {
81 { "disabled", 0 },
82 {}
83 },
84 };
85
86 static const struct ftr_set_desc * const regs[] __initconst = {
87 &mmfr1,
88 &pfr1,
89 &isar1,
90 &kaslr,
91 };
92
93 static const struct {
94 char alias[FTR_ALIAS_NAME_LEN];
95 char feature[FTR_ALIAS_OPTION_LEN];
96 } aliases[] __initconst = {
97 { "kvm-arm.mode=nvhe", "id_aa64mmfr1.vh=0" },
98 { "kvm-arm.mode=protected", "id_aa64mmfr1.vh=0" },
99 { "arm64.nobti", "id_aa64pfr1.bt=0" },
100 { "arm64.nopauth",
101 "id_aa64isar1.gpi=0 id_aa64isar1.gpa=0 "
102 "id_aa64isar1.api=0 id_aa64isar1.apa=0" },
103 { "nokaslr", "kaslr.disabled=1" },
104 };
105
find_field(const char * cmdline,const struct ftr_set_desc * reg,int f,u64 * v)106 static int __init find_field(const char *cmdline,
107 const struct ftr_set_desc *reg, int f, u64 *v)
108 {
109 char opt[FTR_DESC_NAME_LEN + FTR_DESC_FIELD_LEN + 2];
110 int len;
111
112 len = snprintf(opt, ARRAY_SIZE(opt), "%s.%s=",
113 reg->name, reg->fields[f].name);
114
115 if (!parameqn(cmdline, opt, len))
116 return -1;
117
118 return kstrtou64(cmdline + len, 0, v);
119 }
120
match_options(const char * cmdline)121 static void __init match_options(const char *cmdline)
122 {
123 int i;
124
125 for (i = 0; i < ARRAY_SIZE(regs); i++) {
126 int f;
127
128 if (!regs[i]->override)
129 continue;
130
131 for (f = 0; strlen(regs[i]->fields[f].name); f++) {
132 u64 shift = regs[i]->fields[f].shift;
133 u64 mask = 0xfUL << shift;
134 u64 v;
135
136 if (find_field(cmdline, regs[i], f, &v))
137 continue;
138
139 /*
140 * If an override gets filtered out, advertise
141 * it by setting the value to 0xf, but
142 * clearing the mask... Yes, this is fragile.
143 */
144 if (regs[i]->fields[f].filter &&
145 !regs[i]->fields[f].filter(v)) {
146 regs[i]->override->val |= mask;
147 regs[i]->override->mask &= ~mask;
148 continue;
149 }
150
151 regs[i]->override->val &= ~mask;
152 regs[i]->override->val |= (v << shift) & mask;
153 regs[i]->override->mask |= mask;
154
155 return;
156 }
157 }
158 }
159
__parse_cmdline(const char * cmdline,bool parse_aliases)160 static __init void __parse_cmdline(const char *cmdline, bool parse_aliases)
161 {
162 do {
163 char buf[256];
164 size_t len;
165 int i;
166
167 cmdline = skip_spaces(cmdline);
168
169 for (len = 0; cmdline[len] && !isspace(cmdline[len]); len++);
170 if (!len)
171 return;
172
173 len = min(len, ARRAY_SIZE(buf) - 1);
174 strncpy(buf, cmdline, len);
175 buf[len] = 0;
176
177 if (strcmp(buf, "--") == 0)
178 return;
179
180 cmdline += len;
181
182 match_options(buf);
183
184 for (i = 0; parse_aliases && i < ARRAY_SIZE(aliases); i++)
185 if (parameq(buf, aliases[i].alias))
186 __parse_cmdline(aliases[i].feature, false);
187 } while (1);
188 }
189
get_bootargs_cmdline(void)190 static __init const u8 *get_bootargs_cmdline(void)
191 {
192 const u8 *prop;
193 void *fdt;
194 int node;
195
196 fdt = get_early_fdt_ptr();
197 if (!fdt)
198 return NULL;
199
200 node = fdt_path_offset(fdt, "/chosen");
201 if (node < 0)
202 return NULL;
203
204 prop = fdt_getprop(fdt, node, "bootargs", NULL);
205 if (!prop)
206 return NULL;
207
208 return strlen(prop) ? prop : NULL;
209 }
210
parse_cmdline(void)211 static __init void parse_cmdline(void)
212 {
213 const u8 *prop = get_bootargs_cmdline();
214
215 if (IS_ENABLED(CONFIG_CMDLINE_FORCE) || !prop)
216 __parse_cmdline(CONFIG_CMDLINE, true);
217
218 if (!IS_ENABLED(CONFIG_CMDLINE_FORCE) && prop)
219 __parse_cmdline(prop, true);
220 }
221
222 /* Keep checkers quiet */
223 void init_feature_override(void);
224
init_feature_override(void)225 asmlinkage void __init init_feature_override(void)
226 {
227 int i;
228
229 for (i = 0; i < ARRAY_SIZE(regs); i++) {
230 if (regs[i]->override) {
231 regs[i]->override->val = 0;
232 regs[i]->override->mask = 0;
233 }
234 }
235
236 parse_cmdline();
237
238 for (i = 0; i < ARRAY_SIZE(regs); i++) {
239 if (regs[i]->override)
240 __flush_dcache_area(regs[i]->override,
241 sizeof(*regs[i]->override));
242 }
243 }
244