2 * Copyright (c) 2021 The FreeBSD Foundation
4 * This software was developed by Andrew Turner under sponsorship from
5 * the FreeBSD Foundation.
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
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.
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
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.
34 #ifdef __ARM_FEATURE_PAC_DEFAULT
35 #error Must be built with pointer authentication disabled
38 #include <sys/cdefs.h>
39 #include <sys/param.h>
40 #include <sys/kernel.h>
41 #include <sys/libkern.h>
43 #include <sys/reboot.h>
45 #include <machine/armreg.h>
46 #include <machine/cpu.h>
47 #include <machine/reg.h>
48 #include <machine/vmparam.h>
50 #define SCTLR_PTRAUTH (SCTLR_EnIA | SCTLR_EnIB | SCTLR_EnDA | SCTLR_EnDB)
52 static bool __read_mostly enable_ptrauth = false;
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 *);
63 const char *family, *maker, *product;
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)
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.
77 if (strcmp(maker, "Microsoft Corporation") == 0 &&
78 strcmp(family, "Surface") == 0 &&
79 strcmp(product, "Windows Dev Kit 2023") == 0)
92 * Allow the sysadmin to disable pointer authentication globally,
93 * e.g. on broken hardware.
96 TUNABLE_INT_FETCH("hw.pac.enable", &pac_enable);
98 if (boothowto & RB_VERBOSE)
99 printf("Pointer authentication is disabled\n");
103 if (!get_kernel_reg(ID_AA64ISAR1_EL1, &isar1))
106 if (ptrauth_disable())
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.
114 if (ID_AA64ISAR1_APA_VAL(isar1) > 0 ||
115 ID_AA64ISAR1_API_VAL(isar1) > 0) {
116 enable_ptrauth = true;
117 elf64_addr_mask.code |= PAC_ADDR_MASK;
118 elf64_addr_mask.data |= PAC_ADDR_MASK;
122 /* Copy the keys when forking a new process */
124 ptrauth_fork(struct thread *new_td, struct thread *orig_td)
129 memcpy(&new_td->td_md.md_ptrauth_user, &orig_td->td_md.md_ptrauth_user,
130 sizeof(new_td->td_md.md_ptrauth_user));
133 /* Generate new userspace keys when executing a new process */
135 ptrauth_exec(struct thread *td)
140 arc4rand(&td->td_md.md_ptrauth_user, sizeof(td->td_md.md_ptrauth_user),
145 * Copy the user keys when creating a new userspace thread until it's clear
146 * how the ABI expects the various keys to be assigned.
149 ptrauth_copy_thread(struct thread *new_td, struct thread *orig_td)
154 memcpy(&new_td->td_md.md_ptrauth_user, &orig_td->td_md.md_ptrauth_user,
155 sizeof(new_td->td_md.md_ptrauth_user));
158 /* Generate new kernel keys when executing a new kernel thread */
160 ptrauth_thread_alloc(struct thread *td)
165 arc4rand(&td->td_md.md_ptrauth_kern, sizeof(td->td_md.md_ptrauth_kern),
170 * Load the userspace keys. We can't use WRITE_SPECIALREG as we need
171 * to set the architecture extension.
173 #define LOAD_KEY(space, name) \
175 ".arch_extension pauth \n" \
176 "msr "#name"keylo_el1, %0 \n" \
177 "msr "#name"keyhi_el1, %1 \n" \
178 ".arch_extension nopauth \n" \
179 :: "r"(td->td_md.md_ptrauth_##space.name.pa_key_lo), \
180 "r"(td->td_md.md_ptrauth_##space.name.pa_key_hi))
183 ptrauth_thread0(struct thread *td)
188 /* TODO: Generate a random number here */
189 memset(&td->td_md.md_ptrauth_kern, 0,
190 sizeof(td->td_md.md_ptrauth_kern));
191 LOAD_KEY(kern, apia);
193 * No isb as this is called before ptrauth_start so can rely on
194 * the instruction barrier there.
199 * Enable pointer authentication. After this point userspace and the kernel
200 * can sign return addresses, etc. based on their keys
202 * This assumes either all or no CPUs have pointer authentication support,
203 * and, if supported, all CPUs have the same algorithm.
213 /* Enable pointer authentication */
214 sctlr = READ_SPECIALREG(sctlr_el1);
215 sctlr |= SCTLR_PTRAUTH;
216 WRITE_SPECIALREG(sctlr_el1, sctlr);
222 ptrauth_mp_start(uint64_t cpu)
224 struct ptrauth_key start_key;
231 * We need a key until we call sched_throw, however we don't have
232 * a thread until then. Create a key just for use within
233 * init_secondary and whatever it calls. As init_secondary never
234 * returns it is safe to do so from within it.
236 * As it's only used for a short length of time just use the cpu
239 start_key.pa_key_lo = cpu;
240 start_key.pa_key_hi = ~cpu;
243 ".arch_extension pauth \n"
244 "msr apiakeylo_el1, %0 \n"
245 "msr apiakeyhi_el1, %1 \n"
246 ".arch_extension nopauth \n"
247 :: "r"(start_key.pa_key_lo), "r"(start_key.pa_key_hi));
249 /* Enable pointer authentication */
250 sctlr = READ_SPECIALREG(sctlr_el1);
251 sctlr |= SCTLR_PTRAUTH;
252 WRITE_SPECIALREG(sctlr_el1, sctlr);
258 ptrauth_switch(struct thread *td)
260 if (enable_ptrauth) {
261 LOAD_KEY(kern, apia);
268 /* Called when we are exiting uerspace and entering the kernel */
270 ptrauth_exit_el0(struct thread *td)
275 LOAD_KEY(kern, apia);
279 /* Called when we are about to exit the kernel and enter userspace */
281 ptrauth_enter_el0(struct thread *td)
286 LOAD_KEY(user, apia);
287 LOAD_KEY(user, apib);
288 LOAD_KEY(user, apda);
289 LOAD_KEY(user, apdb);
290 LOAD_KEY(user, apga);
292 * No isb as this is called from the exception handler so can rely
293 * on the eret instruction to be the needed context synchronizing event.