// SPDX-License-Identifier: GPL-2.0-only /* * kallsyms.c: in-kernel printing of symbolic oopses and stack traces. * * Rewritten and vastly simplified by Rusty Russell for in-kernel * module loader: * Copyright 2002 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation * * ChangeLog: * * (25/Aug/2004) Paulo Marques <pmarques@grupopie.com> * Changed the compression method from stem compression to "table lookup" * compression (see scripts/kallsyms.c for a more complete description) */ #include <linux/kallsyms.h> #include <linux/init.h> #include <linux/seq_file.h> #include <linux/fs.h> #include <linux/kdb.h> #include <linux/err.h> #include <linux/proc_fs.h> #include <linux/sched.h> /* for cond_resched */ #include <linux/ctype.h> #include <linux/slab.h> #include <linux/filter.h> #include <linux/ftrace.h> #include <linux/kprobes.h> #include <linux/build_bug.h> #include <linux/compiler.h> #include <linux/module.h> #include <linux/kernel.h> #include <linux/bsearch.h> #include <linux/btf_ids.h> #include "kallsyms_internal.h" /* * Expand a compressed symbol data into the resulting uncompressed string, * if uncompressed string is too long (>= maxlen), it will be truncated, * given the offset to where the symbol is in the compressed stream. */ static unsigned int kallsyms_expand_symbol(unsigned int off, char *result, size_t maxlen) { int len, skipped_first = 0; const char *tptr; const u8 *data; /* Get the compressed symbol length from the first symbol byte. */ data = &kallsyms_names[off]; len = *data; data++; off++; /* If MSB is 1, it is a "big" symbol, so needs an additional byte. */ if ((len & 0x80) != 0) { len = (len & 0x7F) | (*data << 7); data++; off++; } /* * Update the offset to return the offset for the next symbol on * the compressed stream. */ off += len; /* * For every byte on the compressed symbol data, copy the table * entry for that byte. */ while (len) { tptr = &kallsyms_token_table[kallsyms_token_index[*data]]; data++; len--; while (*tptr) { if (skipped_first) { if (maxlen <= 1) goto tail; *result = *tptr; result++; maxlen--; } else skipped_first = 1; tptr++; } } tail: if (maxlen) *result = '\0'; /* Return to offset to the next symbol. */ return off; } /* * Get symbol type information. This is encoded as a single char at the * beginning of the symbol name. */ static char kallsyms_get_symbol_type(unsigned int off) { /* * Get just the first code, look it up in the token table, * and return the first char from this token. */ return kallsyms_token_table[kallsyms_token_index[kallsyms_names[off + 1]]]; } /* * Find the offset on the compressed stream given and index in the * kallsyms array. */ static unsigned int get_symbol_offset(unsigned long pos) { const u8 *name; int i, len; /* * Use the closest marker we have. We have markers every 256 positions, * so that should be close enough. */ name = &kallsyms_names[kallsyms_markers[pos >> 8]]; /* * Sequentially scan all the symbols up to the point we're searching * for. Every symbol is stored in a [<len>][<len> bytes of data] format, * so we just need to add the len to the current pointer for every * symbol we wish to skip. */ for (i = 0; i < (pos & 0xFF); i++) { len = *name; /* * If MSB is 1, it is a "big" symbol, so we need to look into * the next byte (and skip it, too). */ if ((len & 0x80) != 0) len = ((len & 0x7F) | (name[1] << 7)) + 1; name = name + len + 1; } return name - kallsyms_names; } unsigned long kallsyms_sym_address(int idx) { /* values are unsigned offsets if --absolute-percpu is not in effect */ if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU)) return kallsyms_relative_base + (u32)kallsyms_offsets[idx]; /* ...otherwise, positive offsets are absolute values */ if (kallsyms_offsets[idx] >= 0) return kallsyms_offsets[idx]; /* ...and negative offsets are relative to kallsyms_relative_base - 1 */ return kallsyms_relative_base - 1 - kallsyms_offsets[idx]; } static unsigned int get_symbol_seq(int index) { unsigned int i, seq = 0; for (i = 0; i < 3; i++) seq = (seq << 8) | kallsyms_seqs_of_names[3 * index + i]; return seq; } static int kallsyms_lookup_names(const char *name, unsigned int *start, unsigned int *end) { int ret; int low, mid, high; unsigned int seq, off; char namebuf[KSYM_NAME_LEN]; low = 0; high = kallsyms_num_syms - 1; while (low <= high) { mid = low + (high - low) / 2; seq = get_symbol_seq(mid); off = get_symbol_offset(seq); kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); ret = strcmp(name, namebuf); if (ret > 0) low = mid + 1; else if (ret < 0) high = mid - 1; else break; } if (low > high) return -ESRCH; low = mid; while (low) { seq = get_symbol_seq(low - 1); off = get_symbol_offset(seq); kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); if (strcmp(name, namebuf)) break; low--; } *start = low; if (end) { high = mid; while (high < kallsyms_num_syms - 1) { seq = get_symbol_seq(high + 1); off = get_symbol_offset(seq); kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); if (strcmp(name, namebuf)) break; high++; } *end = high; } return 0; } /* Lookup the address for this symbol. Returns 0 if not found. */ unsigned long kallsyms_lookup_name(const char *name) { int ret; unsigned int i; /* Skip the search for empty string. */ if (!*name) return 0; ret = kallsyms_lookup_names(name, &i, NULL); if (!ret) return kallsyms_sym_address(get_symbol_seq(i)); return module_kallsyms_lookup_name(name); } /* * Iterate over all symbols in vmlinux. For symbols from modules use * module_kallsyms_on_each_symbol instead. */ int kallsyms_on_each_symbol(int (*fn)(void *, const char *, unsigned long), void *data) { char namebuf[KSYM_NAME_LEN]; unsigned long i; unsigned int off; int ret; for (i = 0, off = 0; i < kallsyms_num_syms; i++) { off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); ret = fn(data, namebuf, kallsyms_sym_address(i)); if (ret != 0) return ret; cond_resched(); } return 0; } int kallsyms_on_each_match_symbol(int (*fn)(void *, unsigned long), const char *name, void *data) { int ret; unsigned int i, start, end; ret = kallsyms_lookup_names(name, &start, &end); if (ret) return 0; for (i = start; !ret && i <= end; i++) { ret = fn(data, kallsyms_sym_address(get_symbol_seq(i))); cond_resched(); } return ret; } static unsigned long get_symbol_pos(unsigned long addr, unsigned long *symbolsize, unsigned long *offset) { unsigned long symbol_start = 0, symbol_end = 0; unsigned long i, low, high, mid; /* Do a binary search on the sorted kallsyms_offsets array. */ low = 0; high = kallsyms_num_syms; while (high - low > 1) { mid = low + (high - low) / 2; if (kallsyms_sym_address(mid) <= addr) low = mid; else high = mid; } /* * Search for the first aliased symbol. Aliased * symbols are symbols with the same address. */ while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low)) --low; symbol_start = kallsyms_sym_address(low); /* Search for next non-aliased symbol. */ for (i = low + 1; i < kallsyms_num_syms; i++) { if (kallsyms_sym_address(i) > symbol_start) { symbol_end = kallsyms_sym_address(i); break; } } /* If we found no next symbol, we use the end of the section. */ if (!symbol_end) { if (is_kernel_inittext(addr)) symbol_end = (unsigned long)_einittext; else if (IS_ENABLED(CONFIG_KALLSYMS_ALL)) symbol_end = (unsigned long)_end; else symbol_end = (unsigned long)_etext; } if (symbolsize) *symbolsize = symbol_end - symbol_start; if (offset) *offset = addr - symbol_start; return low; } /* * Lookup an address but don't bother to find any names. */ int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize, unsigned long *offset) { char namebuf[KSYM_NAME_LEN]; if (is_ksym_addr(addr)) { get_symbol_pos(addr, symbolsize, offset); return 1; } return !!module_address_lookup(addr, symbolsize, offset, NULL, NULL, namebuf) || !!__bpf_address_lookup(addr, symbolsize, offset, namebuf); } static int kallsyms_lookup_buildid(unsigned long addr, unsigned long *symbolsize, unsigned long *offset, char **modname, const unsigned char **modbuildid, char *namebuf) { int ret; namebuf[KSYM_NAME_LEN - 1] = 0; namebuf[0] = 0; if (is_ksym_addr(addr)) { unsigned long pos; pos = get_symbol_pos(addr, symbolsize, offset); /* Grab name */ kallsyms_expand_symbol(get_symbol_offset(pos), namebuf, KSYM_NAME_LEN); if (modname) *modname = NULL; if (modbuildid) *modbuildid = NULL; return strlen(namebuf); } /* See if it's in a module or a BPF JITed image. */ ret = module_address_lookup(addr, symbolsize, offset, modname, modbuildid, namebuf); if (!ret) ret = bpf_address_lookup(addr, symbolsize, offset, modname, namebuf); if (!ret) ret = ftrace_mod_address_lookup(addr, symbolsize, offset, modname, namebuf); return ret; } /* * Lookup an address * - modname is set to NULL if it's in the kernel. * - We guarantee that the returned name is valid until we reschedule even if. * It resides in a module. * - We also guarantee that modname will be valid until rescheduled. */ const char *kallsyms_lookup(unsigned long addr, unsigned long *symbolsize, unsigned long *offset, char **modname, char *namebuf) { int ret = kallsyms_lookup_buildid(addr, symbolsize, offset, modname, NULL, namebuf); if (!ret) return NULL; return namebuf; } int lookup_symbol_name(unsigned long addr, char *symname) { symname[0] = '\0'; symname[KSYM_NAME_LEN - 1] = '\0'; if (is_ksym_addr(addr)) { unsigned long pos; pos = get_symbol_pos(addr, NULL, NULL); /* Grab name */ kallsyms_expand_symbol(get_symbol_offset(pos), symname, KSYM_NAME_LEN); return 0; } /* See if it's in a module. */ return lookup_module_symbol_name(addr, symname); } /* Look up a kernel symbol and return it in a text buffer. */ static int __sprint_symbol(char *buffer, unsigned long address, int symbol_offset, int add_offset, int add_buildid) { char *modname; const unsigned char *buildid; unsigned long offset, size; int len; address += symbol_offset; len = kallsyms_lookup_buildid(address, &size, &offset, &modname, &buildid, buffer); if (!len) return sprintf(buffer, "0x%lx", address - symbol_offset); offset -= symbol_offset; if (add_offset) len += sprintf(buffer + len, "+%#lx/%#lx", offset, size); if (modname) { len += sprintf(buffer + len, " [%s", modname); #if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) if (add_buildid && buildid) { /* build ID should match length of sprintf */ #if IS_ENABLED(CONFIG_MODULES) static_assert(sizeof(typeof_member(struct module, build_id)) == 20); #endif len += sprintf(buffer + len, " %20phN", buildid); } #endif len += sprintf(buffer + len, "]"); } return len; } /** * sprint_symbol - Look up a kernel symbol and return it in a text buffer * @buffer: buffer to be stored * @address: address to lookup * * This function looks up a kernel symbol with @address and stores its name, * offset, size and module name to @buffer if possible. If no symbol was found, * just saves its @address as is. * * This function returns the number of bytes stored in @buffer. */ int sprint_symbol(char *buffer, unsigned long address) { return __sprint_symbol(buffer, address, 0, 1, 0); } EXPORT_SYMBOL_GPL(sprint_symbol); /** * sprint_symbol_build_id - Look up a kernel symbol and return it in a text buffer * @buffer: buffer to be stored * @address: address to lookup * * This function looks up a kernel symbol with @address and stores its name, * offset, size, module name and module build ID to @buffer if possible. If no * symbol was found, just saves its @address as is. * * This function returns the number of bytes stored in @buffer. */ int sprint_symbol_build_id(char *buffer, unsigned long address) { return __sprint_symbol(buffer, address, 0, 1, 1); } EXPORT_SYMBOL_GPL(sprint_symbol_build_id); /** * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer * @buffer: buffer to be stored * @address: address to lookup * * This function looks up a kernel symbol with @address and stores its name * and module name to @buffer if possible. If no symbol was found, just saves * its @address as is. * * This function returns the number of bytes stored in @buffer. */ int sprint_symbol_no_offset(char *buffer, unsigned long address) { return __sprint_symbol(buffer, address, 0, 0, 0); } EXPORT_SYMBOL_GPL(sprint_symbol_no_offset); /** * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer * @buffer: buffer to be stored * @address: address to lookup * * This function is for stack backtrace and does the same thing as * sprint_symbol() but with modified/decreased @address. If there is a * tail-call to the function marked "noreturn", gcc optimized out code after * the call so that the stack-saved return address could point outside of the * caller. This function ensures that kallsyms will find the original caller * by decreasing @address. * * This function returns the number of bytes stored in @buffer. */ int sprint_backtrace(char *buffer, unsigned long address) { return __sprint_symbol(buffer, address, -1, 1, 0); } /** * sprint_backtrace_build_id - Look up a backtrace symbol and return it in a text buffer * @buffer: buffer to be stored * @address: address to lookup * * This function is for stack backtrace and does the same thing as * sprint_symbol() but with modified/decreased @address. If there is a * tail-call to the function marked "noreturn", gcc optimized out code after * the call so that the stack-saved return address could point outside of the * caller. This function ensures that kallsyms will find the original caller * by decreasing @address. This function also appends the module build ID to * the @buffer if @address is within a kernel module. * * This function returns the number of bytes stored in @buffer. */ int sprint_backtrace_build_id(char *buffer, unsigned long address) { return __sprint_symbol(buffer, address, -1, 1, 1); } /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */ struct kallsym_iter { loff_t pos; loff_t pos_mod_end; loff_t pos_ftrace_mod_end; loff_t pos_bpf_end; unsigned long value; unsigned int nameoff; /* If iterating in core kernel symbols. */ char type; char name[KSYM_NAME_LEN]; char module_name[MODULE_NAME_LEN]; int exported; int show_value; }; static int get_ksymbol_mod(struct kallsym_iter *iter) { int ret = module_get_kallsym(iter->pos - kallsyms_num_syms, &iter->value, &iter->type, iter->name, iter->module_name, &iter->exported); if (ret < 0) { iter->pos_mod_end = iter->pos; return 0; } return 1; } /* * ftrace_mod_get_kallsym() may also get symbols for pages allocated for ftrace * purposes. In that case "__builtin__ftrace" is used as a module name, even * though "__builtin__ftrace" is not a module. */ static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter) { int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end, &iter->value, &iter->type, iter->name, iter->module_name, &iter->exported); if (ret < 0) { iter->pos_ftrace_mod_end = iter->pos; return 0; } return 1; } static int get_ksymbol_bpf(struct kallsym_iter *iter) { int ret; strscpy(iter->module_name, "bpf", MODULE_NAME_LEN); iter->exported = 0; ret = bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end, &iter->value, &iter->type, iter->name); if (ret < 0) { iter->pos_bpf_end = iter->pos; return 0; } return 1; } /* * This uses "__builtin__kprobes" as a module name for symbols for pages * allocated for kprobes' purposes, even though "__builtin__kprobes" is not a * module. */ static int get_ksymbol_kprobe(struct kallsym_iter *iter) { strscpy(iter->module_name, "__builtin__kprobes", MODULE_NAME_LEN); iter->exported = 0; return kprobe_get_kallsym(iter->pos - iter->pos_bpf_end, &iter->value, &iter->type, iter->name) < 0 ? 0 : 1; } /* Returns space to next name. */ static unsigned long get_ksymbol_core(struct kallsym_iter *iter) { unsigned off = iter->nameoff; iter->module_name[0] = '\0'; iter->value = kallsyms_sym_address(iter->pos); iter->type = kallsyms_get_symbol_type(off); off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name)); return off - iter->nameoff; } static void reset_iter(struct kallsym_iter *iter, loff_t new_pos) { iter->name[0] = '\0'; iter->nameoff = get_symbol_offset(new_pos); iter->pos = new_pos; if (new_pos == 0) { iter->pos_mod_end = 0; iter->pos_ftrace_mod_end = 0; iter->pos_bpf_end = 0; } } /* * The end position (last + 1) of each additional kallsyms section is recorded * in iter->pos_..._end as each section is added, and so can be used to * determine which get_ksymbol_...() function to call next. */ static int update_iter_mod(struct kallsym_iter *iter, loff_t pos) { iter->pos = pos; if ((!iter->pos_mod_end || iter->pos_mod_end > pos) && get_ksymbol_mod(iter)) return 1; if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) && get_ksymbol_ftrace_mod(iter)) return 1; if ((!iter->pos_bpf_end || iter->pos_bpf_end > pos) && get_ksymbol_bpf(iter)) return 1; return get_ksymbol_kprobe(iter); } /* Returns false if pos at or past end of file. */ static int update_iter(struct kallsym_iter *iter, loff_t pos) { /* Module symbols can be accessed randomly. */ if (pos >= kallsyms_num_syms) return update_iter_mod(iter, pos); /* If we're not on the desired position, reset to new position. */ if (pos != iter->pos) reset_iter(iter, pos); iter->nameoff += get_ksymbol_core(iter); iter->pos++; return 1; } static void *s_next(struct seq_file *m, void *p, loff_t *pos) { (*pos)++; if (!update_iter(m->private, *pos)) return NULL; return p; } static void *s_start(struct seq_file *m, loff_t *pos) { if (!update_iter(m->private, *pos)) return NULL; return m->private; } static void s_stop(struct seq_file *m, void *p) { } static int s_show(struct seq_file *m, void *p) { void *value; struct kallsym_iter *iter = m->private; /* Some debugging symbols have no name. Ignore them. */ if (!iter->name[0]) return 0; value = iter->show_value ? (void *)iter->value : NULL; if (iter->module_name[0]) { char type; /* * Label it "global" if it is exported, * "local" if not exported. */ type = iter->exported ? toupper(iter->type) : tolower(iter->type); seq_printf(m, "%px %c %s\t[%s]\n", value, type, iter->name, iter->module_name); } else seq_printf(m, "%px %c %s\n", value, iter->type, iter->name); return 0; } static const struct seq_operations kallsyms_op = { .start = s_start, .next = s_next, .stop = s_stop, .show = s_show }; #ifdef CONFIG_BPF_SYSCALL struct bpf_iter__ksym { __bpf_md_ptr(struct bpf_iter_meta *, meta); __bpf_md_ptr(struct kallsym_iter *, ksym); }; static int ksym_prog_seq_show(struct seq_file *m, bool in_stop) { struct bpf_iter__ksym ctx; struct bpf_iter_meta meta; struct bpf_prog *prog; meta.seq = m; prog = bpf_iter_get_info(&meta, in_stop); if (!prog) return 0; ctx.meta = &meta; ctx.ksym = m ? m->private : NULL; return bpf_iter_run_prog(prog, &ctx); } static int bpf_iter_ksym_seq_show(struct seq_file *m, void *p) { return ksym_prog_seq_show(m, false); } static void bpf_iter_ksym_seq_stop(struct seq_file *m, void *p) { if (!p) (void) ksym_prog_seq_show(m, true); else s_stop(m, p); } static const struct seq_operations bpf_iter_ksym_ops = { .start = s_start, .next = s_next, .stop = bpf_iter_ksym_seq_stop, .show = bpf_iter_ksym_seq_show, }; static int bpf_iter_ksym_init(void *priv_data, struct bpf_iter_aux_info *aux) { struct kallsym_iter *iter = priv_data; reset_iter(iter, 0); /* cache here as in kallsyms_open() case; use current process * credentials to tell BPF iterators if values should be shown. */ iter->show_value = kallsyms_show_value(current_cred()); return 0; } DEFINE_BPF_ITER_FUNC(ksym, struct bpf_iter_meta *meta, struct kallsym_iter *ksym) static const struct bpf_iter_seq_info ksym_iter_seq_info = { .seq_ops = &bpf_iter_ksym_ops, .init_seq_private = bpf_iter_ksym_init, .fini_seq_private = NULL, .seq_priv_size = sizeof(struct kallsym_iter), }; static struct bpf_iter_reg ksym_iter_reg_info = { .target = "ksym", .feature = BPF_ITER_RESCHED, .ctx_arg_info_size = 1, .ctx_arg_info = { { offsetof(struct bpf_iter__ksym, ksym), PTR_TO_BTF_ID_OR_NULL }, }, .seq_info = &ksym_iter_seq_info, }; BTF_ID_LIST(btf_ksym_iter_id) BTF_ID(struct, kallsym_iter) static int __init bpf_ksym_iter_register(void) { ksym_iter_reg_info.ctx_arg_info[0].btf_id = *btf_ksym_iter_id; return bpf_iter_reg_target(&ksym_iter_reg_info); } late_initcall(bpf_ksym_iter_register); #endif /* CONFIG_BPF_SYSCALL */ static int kallsyms_open(struct inode *inode, struct file *file) { /* * We keep iterator in m->private, since normal case is to * s_start from where we left off, so we avoid doing * using get_symbol_offset for every symbol. */ struct kallsym_iter *iter; iter = __seq_open_private(file, &kallsyms_op, sizeof(*iter)); if (!iter) return -ENOMEM; reset_iter(iter, 0); /* * Instead of checking this on every s_show() call, cache * the result here at open time. */ iter->show_value = kallsyms_show_value(file->f_cred); return 0; } #ifdef CONFIG_KGDB_KDB const char *kdb_walk_kallsyms(loff_t *pos) { static struct kallsym_iter kdb_walk_kallsyms_iter; if (*pos == 0) { memset(&kdb_walk_kallsyms_iter, 0, sizeof(kdb_walk_kallsyms_iter)); reset_iter(&kdb_walk_kallsyms_iter, 0); } while (1) { if (!update_iter(&kdb_walk_kallsyms_iter, *pos)) return NULL; ++*pos; /* Some debugging symbols have no name. Ignore them. */ if (kdb_walk_kallsyms_iter.name[0]) return kdb_walk_kallsyms_iter.name; } } #endif /* CONFIG_KGDB_KDB */ static const struct proc_ops kallsyms_proc_ops = { .proc_open = kallsyms_open, .proc_read = seq_read, .proc_lseek = seq_lseek, .proc_release = seq_release_private, }; static int __init kallsyms_init(void) { proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops); return 0; } device_initcall(kallsyms_init);