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 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__ 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__ */ 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 */ 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 */ 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 */ 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 */ 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 } 174 175 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 */ 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