1 /*-
2 * Copyright (c) 2021 The FreeBSD Foundation
3 *
4 * This software was developed by Andrew Turner under sponsorship from
5 * the FreeBSD Foundation.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29 /*
30 * This manages pointer authentication. As it needs to enable the use of
31 * pointer authentication and change the keys we must built this with
32 * pointer authentication disabled.
33 */
34 #ifdef __ARM_FEATURE_PAC_DEFAULT
35 #error Must be built with pointer authentication disabled
36 #endif
37
38 #include <sys/param.h>
39 #include <sys/kernel.h>
40 #include <sys/libkern.h>
41 #include <sys/proc.h>
42 #include <sys/reboot.h>
43
44 #include <machine/armreg.h>
45 #include <machine/cpu.h>
46 #include <machine/cpu_feat.h>
47 #include <machine/reg.h>
48 #include <machine/vmparam.h>
49
50 #define SCTLR_PTRAUTH (SCTLR_EnIA | SCTLR_EnIB | SCTLR_EnDA | SCTLR_EnDB)
51
52 static bool __read_mostly enable_ptrauth = false;
53
54 /* Functions called from assembly. */
55 void ptrauth_start(void);
56 struct thread *ptrauth_switch(struct thread *);
57 void ptrauth_exit_el0(struct thread *);
58 void ptrauth_enter_el0(struct thread *);
59
60 static bool
ptrauth_disable(void)61 ptrauth_disable(void)
62 {
63 const char *family, *maker, *product;
64
65 family = kern_getenv("smbios.system.family");
66 maker = kern_getenv("smbios.system.maker");
67 product = kern_getenv("smbios.system.product");
68 if (family == NULL || maker == NULL || product == NULL)
69 return (false);
70
71 /*
72 * The Dev Kit appears to be configured to trap upon access to PAC
73 * registers, but the kernel boots at EL1 and so we have no way to
74 * inspect or change this configuration. As a workaround, simply
75 * disable PAC on this platform.
76 */
77 if (strcmp(maker, "Microsoft Corporation") == 0 &&
78 strcmp(family, "Surface") == 0 &&
79 strcmp(product, "Windows Dev Kit 2023") == 0)
80 return (true);
81
82 return (false);
83 }
84
85 static bool
ptrauth_check(const struct cpu_feat * feat __unused,u_int midr __unused)86 ptrauth_check(const struct cpu_feat *feat __unused, u_int midr __unused)
87 {
88 uint64_t isar1;
89 int pac_enable;
90
91 /*
92 * Allow the sysadmin to disable pointer authentication globally,
93 * e.g. on broken hardware.
94 */
95 pac_enable = 1;
96 TUNABLE_INT_FETCH("hw.pac.enable", &pac_enable);
97 if (!pac_enable) {
98 if (boothowto & RB_VERBOSE)
99 printf("Pointer authentication is disabled\n");
100 return (false);
101 }
102
103 if (!get_kernel_reg(ID_AA64ISAR1_EL1, &isar1))
104 return (false);
105
106 if (ptrauth_disable())
107 return (false);
108
109 /*
110 * This assumes if there is pointer authentication on the boot CPU
111 * it will also be available on any non-boot CPUs. If this is ever
112 * not the case we will have to add a quirk.
113 */
114 return (ID_AA64ISAR1_APA_VAL(isar1) > 0 ||
115 ID_AA64ISAR1_API_VAL(isar1) > 0);
116 }
117
118 static void
ptrauth_enable(const struct cpu_feat * feat __unused,cpu_feat_errata errata_status __unused,u_int * errata_list __unused,u_int errata_count __unused)119 ptrauth_enable(const struct cpu_feat *feat __unused,
120 cpu_feat_errata errata_status __unused, u_int *errata_list __unused,
121 u_int errata_count __unused)
122 {
123 enable_ptrauth = true;
124 elf64_addr_mask.code |= PAC_ADDR_MASK;
125 elf64_addr_mask.data |= PAC_ADDR_MASK;
126 }
127
128
129 static struct cpu_feat feat_pauth = {
130 .feat_name = "FEAT_PAuth",
131 .feat_check = ptrauth_check,
132 .feat_enable = ptrauth_enable,
133 .feat_flags = CPU_FEAT_EARLY_BOOT | CPU_FEAT_SYSTEM,
134 };
135 DATA_SET(cpu_feat_set, feat_pauth);
136
137 /* Copy the keys when forking a new process */
138 void
ptrauth_fork(struct thread * new_td,struct thread * orig_td)139 ptrauth_fork(struct thread *new_td, struct thread *orig_td)
140 {
141 if (!enable_ptrauth)
142 return;
143
144 memcpy(&new_td->td_md.md_ptrauth_user, &orig_td->td_md.md_ptrauth_user,
145 sizeof(new_td->td_md.md_ptrauth_user));
146 }
147
148 /* Generate new userspace keys when executing a new process */
149 void
ptrauth_exec(struct thread * td)150 ptrauth_exec(struct thread *td)
151 {
152 if (!enable_ptrauth)
153 return;
154
155 arc4rand(&td->td_md.md_ptrauth_user, sizeof(td->td_md.md_ptrauth_user),
156 0);
157 }
158
159 /*
160 * Copy the user keys when creating a new userspace thread until it's clear
161 * how the ABI expects the various keys to be assigned.
162 */
163 void
ptrauth_copy_thread(struct thread * new_td,struct thread * orig_td)164 ptrauth_copy_thread(struct thread *new_td, struct thread *orig_td)
165 {
166 if (!enable_ptrauth)
167 return;
168
169 memcpy(&new_td->td_md.md_ptrauth_user, &orig_td->td_md.md_ptrauth_user,
170 sizeof(new_td->td_md.md_ptrauth_user));
171 }
172
173 /* Generate new kernel keys when executing a new kernel thread */
174 void
ptrauth_thread_alloc(struct thread * td)175 ptrauth_thread_alloc(struct thread *td)
176 {
177 if (!enable_ptrauth)
178 return;
179
180 arc4rand(&td->td_md.md_ptrauth_kern, sizeof(td->td_md.md_ptrauth_kern),
181 0);
182 }
183
184 /*
185 * Load the userspace keys. We can't use WRITE_SPECIALREG as we need
186 * to set the architecture extension.
187 */
188 #define LOAD_KEY(space, name, reg) \
189 __asm __volatile( \
190 "msr "__XSTRING(MRS_REG_ALT_NAME(reg ## KeyLo_EL1))", %0 \n" \
191 "msr "__XSTRING(MRS_REG_ALT_NAME(reg ## KeyHi_EL1))", %1 \n" \
192 :: "r"(td->td_md.md_ptrauth_##space.name.pa_key_lo), \
193 "r"(td->td_md.md_ptrauth_##space.name.pa_key_hi))
194
195 void
ptrauth_thread0(struct thread * td)196 ptrauth_thread0(struct thread *td)
197 {
198 if (!enable_ptrauth)
199 return;
200
201 /* TODO: Generate a random number here */
202 memset(&td->td_md.md_ptrauth_kern, 0,
203 sizeof(td->td_md.md_ptrauth_kern));
204 LOAD_KEY(kern, apia, APIA);
205 /*
206 * No isb as this is called before ptrauth_start so can rely on
207 * the instruction barrier there.
208 */
209 }
210
211 /*
212 * Enable pointer authentication. After this point userspace and the kernel
213 * can sign return addresses, etc. based on their keys
214 *
215 * This assumes either all or no CPUs have pointer authentication support,
216 * and, if supported, all CPUs have the same algorithm.
217 */
218 void
ptrauth_start(void)219 ptrauth_start(void)
220 {
221 uint64_t sctlr;
222
223 if (!enable_ptrauth)
224 return;
225
226 /* Enable pointer authentication */
227 sctlr = READ_SPECIALREG(sctlr_el1);
228 sctlr |= SCTLR_PTRAUTH;
229 WRITE_SPECIALREG(sctlr_el1, sctlr);
230 isb();
231 }
232
233 #ifdef SMP
234 void
ptrauth_mp_start(uint64_t cpu)235 ptrauth_mp_start(uint64_t cpu)
236 {
237 struct ptrauth_key start_key;
238 uint64_t sctlr;
239
240 if (!enable_ptrauth)
241 return;
242
243 /*
244 * We need a key until we call sched_throw, however we don't have
245 * a thread until then. Create a key just for use within
246 * init_secondary and whatever it calls. As init_secondary never
247 * returns it is safe to do so from within it.
248 *
249 * As it's only used for a short length of time just use the cpu
250 * as the key.
251 */
252 start_key.pa_key_lo = cpu;
253 start_key.pa_key_hi = ~cpu;
254
255 __asm __volatile(
256 ".arch_extension pauth \n"
257 "msr "__XSTRING(APIAKeyLo_EL1_REG)", %0 \n"
258 "msr "__XSTRING(APIAKeyHi_EL1_REG)", %1 \n"
259 ".arch_extension nopauth \n"
260 :: "r"(start_key.pa_key_lo), "r"(start_key.pa_key_hi));
261
262 /* Enable pointer authentication */
263 sctlr = READ_SPECIALREG(sctlr_el1);
264 sctlr |= SCTLR_PTRAUTH;
265 WRITE_SPECIALREG(sctlr_el1, sctlr);
266 isb();
267 }
268 #endif
269
270 struct thread *
ptrauth_switch(struct thread * td)271 ptrauth_switch(struct thread *td)
272 {
273 if (enable_ptrauth) {
274 LOAD_KEY(kern, apia, APIA);
275 isb();
276 }
277
278 return (td);
279 }
280
281 /* Called when we are exiting uerspace and entering the kernel */
282 void
ptrauth_exit_el0(struct thread * td)283 ptrauth_exit_el0(struct thread *td)
284 {
285 if (!enable_ptrauth)
286 return;
287
288 LOAD_KEY(kern, apia, APIA);
289 isb();
290 }
291
292 /* Called when we are about to exit the kernel and enter userspace */
293 void
ptrauth_enter_el0(struct thread * td)294 ptrauth_enter_el0(struct thread *td)
295 {
296 if (!enable_ptrauth)
297 return;
298
299 LOAD_KEY(user, apia, APIA);
300 LOAD_KEY(user, apib, APIB);
301 LOAD_KEY(user, apda, APDA);
302 LOAD_KEY(user, apdb, APDB);
303 LOAD_KEY(user, apga, APGA);
304 /*
305 * No isb as this is called from the exception handler so can rely
306 * on the eret instruction to be the needed context synchronizing event.
307 */
308 }
309