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/param.h>
39 #include <sys/kernel.h>
40 #include <sys/libkern.h>
42 #include <sys/reboot.h>
44 #include <machine/armreg.h>
45 #include <machine/cpu.h>
46 #include <machine/reg.h>
47 #include <machine/vmparam.h>
49 #define SCTLR_PTRAUTH (SCTLR_EnIA | SCTLR_EnIB | SCTLR_EnDA | SCTLR_EnDB)
51 static bool __read_mostly enable_ptrauth = false;
53 /* Functions called from assembly. */
54 void ptrauth_start(void);
55 struct thread *ptrauth_switch(struct thread *);
56 void ptrauth_exit_el0(struct thread *);
57 void ptrauth_enter_el0(struct thread *);
62 const char *family, *maker, *product;
64 family = kern_getenv("smbios.system.family");
65 maker = kern_getenv("smbios.system.maker");
66 product = kern_getenv("smbios.system.product");
67 if (family == NULL || maker == NULL || product == NULL)
71 * The Dev Kit appears to be configured to trap upon access to PAC
72 * registers, but the kernel boots at EL1 and so we have no way to
73 * inspect or change this configuration. As a workaround, simply
74 * disable PAC on this platform.
76 if (strcmp(maker, "Microsoft Corporation") == 0 &&
77 strcmp(family, "Surface") == 0 &&
78 strcmp(product, "Windows Dev Kit 2023") == 0)
91 * Allow the sysadmin to disable pointer authentication globally,
92 * e.g. on broken hardware.
95 TUNABLE_INT_FETCH("hw.pac.enable", &pac_enable);
97 if (boothowto & RB_VERBOSE)
98 printf("Pointer authentication is disabled\n");
102 if (!get_kernel_reg(ID_AA64ISAR1_EL1, &isar1))
105 if (ptrauth_disable())
109 * This assumes if there is pointer authentication on the boot CPU
110 * it will also be available on any non-boot CPUs. If this is ever
111 * not the case we will have to add a quirk.
113 if (ID_AA64ISAR1_APA_VAL(isar1) > 0 ||
114 ID_AA64ISAR1_API_VAL(isar1) > 0) {
115 enable_ptrauth = true;
116 elf64_addr_mask.code |= PAC_ADDR_MASK;
117 elf64_addr_mask.data |= PAC_ADDR_MASK;
121 /* Copy the keys when forking a new process */
123 ptrauth_fork(struct thread *new_td, struct thread *orig_td)
128 memcpy(&new_td->td_md.md_ptrauth_user, &orig_td->td_md.md_ptrauth_user,
129 sizeof(new_td->td_md.md_ptrauth_user));
132 /* Generate new userspace keys when executing a new process */
134 ptrauth_exec(struct thread *td)
139 arc4rand(&td->td_md.md_ptrauth_user, sizeof(td->td_md.md_ptrauth_user),
144 * Copy the user keys when creating a new userspace thread until it's clear
145 * how the ABI expects the various keys to be assigned.
148 ptrauth_copy_thread(struct thread *new_td, struct thread *orig_td)
153 memcpy(&new_td->td_md.md_ptrauth_user, &orig_td->td_md.md_ptrauth_user,
154 sizeof(new_td->td_md.md_ptrauth_user));
157 /* Generate new kernel keys when executing a new kernel thread */
159 ptrauth_thread_alloc(struct thread *td)
164 arc4rand(&td->td_md.md_ptrauth_kern, sizeof(td->td_md.md_ptrauth_kern),
169 * Load the userspace keys. We can't use WRITE_SPECIALREG as we need
170 * to set the architecture extension.
172 #define LOAD_KEY(space, name) \
174 ".arch_extension pauth \n" \
175 "msr "#name"keylo_el1, %0 \n" \
176 "msr "#name"keyhi_el1, %1 \n" \
177 ".arch_extension nopauth \n" \
178 :: "r"(td->td_md.md_ptrauth_##space.name.pa_key_lo), \
179 "r"(td->td_md.md_ptrauth_##space.name.pa_key_hi))
182 ptrauth_thread0(struct thread *td)
187 /* TODO: Generate a random number here */
188 memset(&td->td_md.md_ptrauth_kern, 0,
189 sizeof(td->td_md.md_ptrauth_kern));
190 LOAD_KEY(kern, apia);
192 * No isb as this is called before ptrauth_start so can rely on
193 * the instruction barrier there.
198 * Enable pointer authentication. After this point userspace and the kernel
199 * can sign return addresses, etc. based on their keys
201 * This assumes either all or no CPUs have pointer authentication support,
202 * and, if supported, all CPUs have the same algorithm.
212 /* Enable pointer authentication */
213 sctlr = READ_SPECIALREG(sctlr_el1);
214 sctlr |= SCTLR_PTRAUTH;
215 WRITE_SPECIALREG(sctlr_el1, sctlr);
221 ptrauth_mp_start(uint64_t cpu)
223 struct ptrauth_key start_key;
230 * We need a key until we call sched_throw, however we don't have
231 * a thread until then. Create a key just for use within
232 * init_secondary and whatever it calls. As init_secondary never
233 * returns it is safe to do so from within it.
235 * As it's only used for a short length of time just use the cpu
238 start_key.pa_key_lo = cpu;
239 start_key.pa_key_hi = ~cpu;
242 ".arch_extension pauth \n"
243 "msr apiakeylo_el1, %0 \n"
244 "msr apiakeyhi_el1, %1 \n"
245 ".arch_extension nopauth \n"
246 :: "r"(start_key.pa_key_lo), "r"(start_key.pa_key_hi));
248 /* Enable pointer authentication */
249 sctlr = READ_SPECIALREG(sctlr_el1);
250 sctlr |= SCTLR_PTRAUTH;
251 WRITE_SPECIALREG(sctlr_el1, sctlr);
257 ptrauth_switch(struct thread *td)
259 if (enable_ptrauth) {
260 LOAD_KEY(kern, apia);
267 /* Called when we are exiting uerspace and entering the kernel */
269 ptrauth_exit_el0(struct thread *td)
274 LOAD_KEY(kern, apia);
278 /* Called when we are about to exit the kernel and enter userspace */
280 ptrauth_enter_el0(struct thread *td)
285 LOAD_KEY(user, apia);
286 LOAD_KEY(user, apib);
287 LOAD_KEY(user, apda);
288 LOAD_KEY(user, apdb);
289 LOAD_KEY(user, apga);
291 * No isb as this is called from the exception handler so can rely
292 * on the eret instruction to be the needed context synchronizing event.