1 /*
2 * Copyright (c) 2018-2020, ARM Limited and Contributors. All rights reserved.
3 *
4 * SPDX-License-Identifier: BSD-3-Clause
5 */
6
7 #include <assert.h>
8 #include <stdbool.h>
9 #include <stdint.h>
10
11 #include <arch_helpers.h>
12 #include <common/debug.h>
13 #include <drivers/console.h>
14
15 /* Maximum number of entries in the backtrace to display */
16 #define UNWIND_LIMIT 20U
17
18 /*
19 * If -fno-omit-frame-pointer is used:
20 *
21 * - AArch64: The AAPCS defines the format of the frame records and mandates the
22 * usage of r29 as frame pointer.
23 *
24 * - AArch32: The format of the frame records is not defined in the AAPCS.
25 * However, at least GCC and Clang use the same format. When they are forced
26 * to only generate A32 code (with -marm), they use r11 as frame pointer and a
27 * similar format as in AArch64. If interworking with T32 is enabled, the
28 * frame pointer is r7 and the format is different. This is not supported by
29 * this implementation of backtrace, so it is needed to use -marm.
30 */
31
32 /* Frame records form a linked list in the stack */
33 struct frame_record {
34 /* Previous frame record in the list */
35 struct frame_record *parent;
36 /* Return address of the function at this level */
37 uintptr_t return_addr;
38 };
39
get_el_str(unsigned int el)40 const char *get_el_str(unsigned int el)
41 {
42 if (el == 3U) {
43 return "EL3";
44 } else if (el == 2U) {
45 return "EL2";
46 } else {
47 return "S-EL1";
48 }
49 }
50
51 /*
52 * Returns true if the address points to a virtual address that can be read at
53 * the current EL, false otherwise.
54 */
55 #ifdef __aarch64__
is_address_readable(uintptr_t addr)56 static bool is_address_readable(uintptr_t addr)
57 {
58 unsigned int el = get_current_el();
59
60 #if ENABLE_PAUTH
61 /*
62 * When pointer authentication is enabled, the LR value saved on the
63 * stack contains a PAC. It must be stripped to retrieve the return
64 * address.
65 */
66 xpaci(addr);
67 #endif
68 if (el == 3U) {
69 ats1e3r(addr);
70 } else if (el == 2U) {
71 ats1e2r(addr);
72 } else {
73 AT(ats1e1r, addr);
74 }
75
76 isb();
77
78 /* If PAR.F == 1 the address translation was aborted. */
79 if ((read_par_el1() & PAR_F_MASK) != 0U)
80 return false;
81
82 return true;
83 }
84 #else /* !__aarch64__ */
is_address_readable(uintptr_t addr)85 static bool is_address_readable(uintptr_t addr)
86 {
87 unsigned int el = get_current_el();
88
89 if (el == 3U) {
90 write_ats1cpr(addr);
91 } else if (el == 2U) {
92 write_ats1hr(addr);
93 } else {
94 write_ats1cpr(addr);
95 }
96
97 isb();
98
99 /* If PAR.F == 1 the address translation was aborted. */
100 if ((read64_par() & PAR_F_MASK) != 0U)
101 return false;
102
103 return true;
104 }
105 #endif /* __aarch64__ */
106
107 /*
108 * Returns true if all the bytes in a given object are in mapped memory and an
109 * LDR using this pointer would succeed, false otherwise.
110 */
is_valid_object(uintptr_t addr,size_t size)111 static bool is_valid_object(uintptr_t addr, size_t size)
112 {
113 assert(size > 0U);
114
115 if (addr == 0U)
116 return false;
117
118 /* Detect overflows */
119 if ((addr + size) < addr)
120 return false;
121
122 /* A pointer not aligned properly could trigger an alignment fault. */
123 if ((addr & (sizeof(uintptr_t) - 1U)) != 0U)
124 return false;
125
126 /* Check that all the object is readable */
127 for (size_t i = 0; i < size; i++) {
128 if (!is_address_readable(addr + i))
129 return false;
130 }
131
132 return true;
133 }
134
135 /*
136 * Returns true if the specified address is correctly aligned and points to a
137 * valid memory region.
138 */
is_valid_jump_address(uintptr_t addr)139 static bool is_valid_jump_address(uintptr_t addr)
140 {
141 if (addr == 0U)
142 return false;
143
144 /* Check alignment. Both A64 and A32 use 32-bit opcodes */
145 if ((addr & (sizeof(uint32_t) - 1U)) != 0U)
146 return false;
147
148 if (!is_address_readable(addr))
149 return false;
150
151 return true;
152 }
153
154 /*
155 * Returns true if the pointer points at a valid frame record, false otherwise.
156 */
is_valid_frame_record(struct frame_record * fr)157 static bool is_valid_frame_record(struct frame_record *fr)
158 {
159 return is_valid_object((uintptr_t)fr, sizeof(struct frame_record));
160 }
161
162 /*
163 * Adjust the frame-pointer-register value by 4 bytes on AArch32 to have the
164 * same layout as AArch64.
165 */
adjust_frame_record(struct frame_record * fr)166 static struct frame_record *adjust_frame_record(struct frame_record *fr)
167 {
168 #ifdef __aarch64__
169 return fr;
170 #else
171 return (struct frame_record *)((uintptr_t)fr - 4U);
172 #endif
173 }
174
unwind_stack(struct frame_record * fr,uintptr_t current_pc,uintptr_t link_register)175 static void unwind_stack(struct frame_record *fr, uintptr_t current_pc,
176 uintptr_t link_register)
177 {
178 uintptr_t call_site;
179 static const char *backtrace_str = "%u: %s: 0x%lx\n";
180 const char *el_str = get_el_str(get_current_el());
181
182 if (!is_valid_frame_record(fr)) {
183 printf("ERROR: Corrupted frame pointer (frame record address = %p)\n",
184 fr);
185 return;
186 }
187
188 if (fr->return_addr != link_register) {
189 printf("ERROR: Corrupted stack (frame record address = %p)\n",
190 fr);
191 return;
192 }
193
194 /* The level 0 of the backtrace is the current backtrace function */
195 printf(backtrace_str, 0U, el_str, current_pc);
196
197 /*
198 * The last frame record pointer in the linked list at the beginning of
199 * the stack should be NULL unless stack is corrupted.
200 */
201 for (unsigned int i = 1U; i < UNWIND_LIMIT; i++) {
202 /* If an invalid frame record is found, exit. */
203 if (!is_valid_frame_record(fr))
204 return;
205 /*
206 * A32 and A64 are fixed length so the address from where the
207 * call was made is the instruction before the return address,
208 * which is always 4 bytes before it.
209 */
210 call_site = fr->return_addr - 4U;
211
212 #if ENABLE_PAUTH
213 /*
214 * When pointer authentication is enabled, the LR value saved on
215 * the stack contains a PAC. It must be stripped to retrieve the
216 * return address.
217 */
218 xpaci(call_site);
219 #endif
220 /*
221 * If the address is invalid it means that the frame record is
222 * probably corrupted.
223 */
224 if (!is_valid_jump_address(call_site))
225 return;
226
227 printf(backtrace_str, i, el_str, call_site);
228
229 fr = adjust_frame_record(fr->parent);
230 }
231
232 printf("ERROR: Max backtrace depth reached\n");
233 }
234
235 /*
236 * Display a backtrace. The cookie string parameter is displayed along the
237 * trace to help filter the log messages.
238 *
239 * Many things can prevent displaying the expected backtrace. For example,
240 * compiler optimizations can use a branch instead of branch with link when it
241 * detects a tail call. The backtrace level for this caller will not be
242 * displayed, as it does not appear in the call stack anymore. Also, assembly
243 * functions will not be displayed unless they setup AAPCS compliant frame
244 * records on AArch64 and compliant with GCC-specific frame record format on
245 * AArch32.
246 *
247 * Usage of the trace: addr2line can be used to map the addresses to function
248 * and source code location when given the ELF file compiled with debug
249 * information. The "-i" flag is highly recommended to improve display of
250 * inlined function. The *.dump files generated when building each image can
251 * also be used.
252 *
253 * WARNING: In case of corrupted stack, this function could display security
254 * sensitive information past the beginning of the stack so it must not be used
255 * in production build. This function is only compiled in when ENABLE_BACKTRACE
256 * is set to 1.
257 */
backtrace(const char * cookie)258 void backtrace(const char *cookie)
259 {
260 uintptr_t return_address = (uintptr_t)__builtin_return_address(0U);
261 struct frame_record *fr = __builtin_frame_address(0U);
262
263 /* Printing the backtrace may crash the system, flush before starting */
264 console_flush();
265
266 fr = adjust_frame_record(fr);
267
268 printf("BACKTRACE: START: %s\n", cookie);
269
270 unwind_stack(fr, (uintptr_t)&backtrace, return_address);
271
272 printf("BACKTRACE: END: %s\n", cookie);
273 }
274