// SPDX-License-Identifier: GPL-2.0-or-later /* * Module kallsyms support * * Copyright (C) 2010 Rusty Russell */ #include <linux/module.h> #include <linux/kallsyms.h> #include <linux/buildid.h> #include <linux/bsearch.h> #include "internal.h" /* Lookup exported symbol in given range of kernel_symbols */ static const struct kernel_symbol *lookup_exported_symbol(const char *name, const struct kernel_symbol *start, const struct kernel_symbol *stop) { return bsearch(name, start, stop - start, sizeof(struct kernel_symbol), cmp_name); } static int is_exported(const char *name, unsigned long value, const struct module *mod) { const struct kernel_symbol *ks; if (!mod) ks = lookup_exported_symbol(name, __start___ksymtab, __stop___ksymtab); else ks = lookup_exported_symbol(name, mod->syms, mod->syms + mod->num_syms); return ks && kernel_symbol_value(ks) == value; } /* As per nm */ static char elf_type(const Elf_Sym *sym, const struct load_info *info) { const Elf_Shdr *sechdrs = info->sechdrs; if (ELF_ST_BIND(sym->st_info) == STB_WEAK) { if (ELF_ST_TYPE(sym->st_info) == STT_OBJECT) return 'v'; else return 'w'; } if (sym->st_shndx == SHN_UNDEF) return 'U'; if (sym->st_shndx == SHN_ABS || sym->st_shndx == info->index.pcpu) return 'a'; if (sym->st_shndx >= SHN_LORESERVE) return '?'; if (sechdrs[sym->st_shndx].sh_flags & SHF_EXECINSTR) return 't'; if (sechdrs[sym->st_shndx].sh_flags & SHF_ALLOC && sechdrs[sym->st_shndx].sh_type != SHT_NOBITS) { if (!(sechdrs[sym->st_shndx].sh_flags & SHF_WRITE)) return 'r'; else if (sechdrs[sym->st_shndx].sh_flags & ARCH_SHF_SMALL) return 'g'; else return 'd'; } if (sechdrs[sym->st_shndx].sh_type == SHT_NOBITS) { if (sechdrs[sym->st_shndx].sh_flags & ARCH_SHF_SMALL) return 's'; else return 'b'; } if (strstarts(info->secstrings + sechdrs[sym->st_shndx].sh_name, ".debug")) { return 'n'; } return '?'; } static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs, unsigned int shnum, unsigned int pcpundx) { const Elf_Shdr *sec; if (src->st_shndx == SHN_UNDEF || src->st_shndx >= shnum || !src->st_name) return false; #ifdef CONFIG_KALLSYMS_ALL if (src->st_shndx == pcpundx) return true; #endif sec = sechdrs + src->st_shndx; if (!(sec->sh_flags & SHF_ALLOC) #ifndef CONFIG_KALLSYMS_ALL || !(sec->sh_flags & SHF_EXECINSTR) #endif || (sec->sh_entsize & INIT_OFFSET_MASK)) return false; return true; } /* * We only allocate and copy the strings needed by the parts of symtab * we keep. This is simple, but has the effect of making multiple * copies of duplicates. We could be more sophisticated, see * linux-kernel thread starting with * <73defb5e4bca04a6431392cc341112b1@localhost>. */ void layout_symtab(struct module *mod, struct load_info *info) { Elf_Shdr *symsect = info->sechdrs + info->index.sym; Elf_Shdr *strsect = info->sechdrs + info->index.str; const Elf_Sym *src; unsigned int i, nsrc, ndst, strtab_size = 0; /* Put symbol section at end of init part of module. */ symsect->sh_flags |= SHF_ALLOC; symsect->sh_entsize = module_get_offset(mod, &mod->init_layout.size, symsect, info->index.sym) | INIT_OFFSET_MASK; pr_debug("\t%s\n", info->secstrings + symsect->sh_name); src = (void *)info->hdr + symsect->sh_offset; nsrc = symsect->sh_size / sizeof(*src); /* Compute total space required for the core symbols' strtab. */ for (ndst = i = 0; i < nsrc; i++) { if (i == 0 || is_livepatch_module(mod) || is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum, info->index.pcpu)) { strtab_size += strlen(&info->strtab[src[i].st_name]) + 1; ndst++; } } /* Append room for core symbols at end of core part. */ info->symoffs = ALIGN(mod->data_layout.size, symsect->sh_addralign ?: 1); info->stroffs = mod->data_layout.size = info->symoffs + ndst * sizeof(Elf_Sym); mod->data_layout.size += strtab_size; /* Note add_kallsyms() computes strtab_size as core_typeoffs - stroffs */ info->core_typeoffs = mod->data_layout.size; mod->data_layout.size += ndst * sizeof(char); mod->data_layout.size = strict_align(mod->data_layout.size); /* Put string table section at end of init part of module. */ strsect->sh_flags |= SHF_ALLOC; strsect->sh_entsize = module_get_offset(mod, &mod->init_layout.size, strsect, info->index.str) | INIT_OFFSET_MASK; pr_debug("\t%s\n", info->secstrings + strsect->sh_name); /* We'll tack temporary mod_kallsyms on the end. */ mod->init_layout.size = ALIGN(mod->init_layout.size, __alignof__(struct mod_kallsyms)); info->mod_kallsyms_init_off = mod->init_layout.size; mod->init_layout.size += sizeof(struct mod_kallsyms); info->init_typeoffs = mod->init_layout.size; mod->init_layout.size += nsrc * sizeof(char); mod->init_layout.size = strict_align(mod->init_layout.size); } /* * We use the full symtab and strtab which layout_symtab arranged to * be appended to the init section. Later we switch to the cut-down * core-only ones. */ void add_kallsyms(struct module *mod, const struct load_info *info) { unsigned int i, ndst; const Elf_Sym *src; Elf_Sym *dst; char *s; Elf_Shdr *symsec = &info->sechdrs[info->index.sym]; unsigned long strtab_size; /* Set up to point into init section. */ mod->kallsyms = (void __rcu *)mod->init_layout.base + info->mod_kallsyms_init_off; rcu_read_lock(); /* The following is safe since this pointer cannot change */ rcu_dereference(mod->kallsyms)->symtab = (void *)symsec->sh_addr; rcu_dereference(mod->kallsyms)->num_symtab = symsec->sh_size / sizeof(Elf_Sym); /* Make sure we get permanent strtab: don't use info->strtab. */ rcu_dereference(mod->kallsyms)->strtab = (void *)info->sechdrs[info->index.str].sh_addr; rcu_dereference(mod->kallsyms)->typetab = mod->init_layout.base + info->init_typeoffs; /* * Now populate the cut down core kallsyms for after init * and set types up while we still have access to sections. */ mod->core_kallsyms.symtab = dst = mod->data_layout.base + info->symoffs; mod->core_kallsyms.strtab = s = mod->data_layout.base + info->stroffs; mod->core_kallsyms.typetab = mod->data_layout.base + info->core_typeoffs; strtab_size = info->core_typeoffs - info->stroffs; src = rcu_dereference(mod->kallsyms)->symtab; for (ndst = i = 0; i < rcu_dereference(mod->kallsyms)->num_symtab; i++) { rcu_dereference(mod->kallsyms)->typetab[i] = elf_type(src + i, info); if (i == 0 || is_livepatch_module(mod) || is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum, info->index.pcpu)) { ssize_t ret; mod->core_kallsyms.typetab[ndst] = rcu_dereference(mod->kallsyms)->typetab[i]; dst[ndst] = src[i]; dst[ndst++].st_name = s - mod->core_kallsyms.strtab; ret = strscpy(s, &rcu_dereference(mod->kallsyms)->strtab[src[i].st_name], strtab_size); if (ret < 0) break; s += ret + 1; strtab_size -= ret + 1; } } rcu_read_unlock(); mod->core_kallsyms.num_symtab = ndst; } #if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) void init_build_id(struct module *mod, const struct load_info *info) { const Elf_Shdr *sechdr; unsigned int i; for (i = 0; i < info->hdr->e_shnum; i++) { sechdr = &info->sechdrs[i]; if (!sect_empty(sechdr) && sechdr->sh_type == SHT_NOTE && !build_id_parse_buf((void *)sechdr->sh_addr, mod->build_id, sechdr->sh_size)) break; } } #else void init_build_id(struct module *mod, const struct load_info *info) { } #endif /* * This ignores the intensely annoying "mapping symbols" found * in ARM ELF files: $a, $t and $d. */ static inline int is_arm_mapping_symbol(const char *str) { if (str[0] == '.' && str[1] == 'L') return true; return str[0] == '$' && strchr("axtd", str[1]) && (str[2] == '\0' || str[2] == '.'); } static const char *kallsyms_symbol_name(struct mod_kallsyms *kallsyms, unsigned int symnum) { return kallsyms->strtab + kallsyms->symtab[symnum].st_name; } /* * Given a module and address, find the corresponding symbol and return its name * while providing its size and offset if needed. */ static const char *find_kallsyms_symbol(struct module *mod, unsigned long addr, unsigned long *size, unsigned long *offset) { unsigned int i, best = 0; unsigned long nextval, bestval; struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms); /* At worse, next value is at end of module */ if (within_module_init(addr, mod)) nextval = (unsigned long)mod->init_layout.base + mod->init_layout.text_size; else nextval = (unsigned long)mod->core_layout.base + mod->core_layout.text_size; bestval = kallsyms_symbol_value(&kallsyms->symtab[best]); /* * Scan for closest preceding symbol, and next symbol. (ELF * starts real symbols at 1). */ for (i = 1; i < kallsyms->num_symtab; i++) { const Elf_Sym *sym = &kallsyms->symtab[i]; unsigned long thisval = kallsyms_symbol_value(sym); if (sym->st_shndx == SHN_UNDEF) continue; /* * We ignore unnamed symbols: they're uninformative * and inserted at a whim. */ if (*kallsyms_symbol_name(kallsyms, i) == '\0' || is_arm_mapping_symbol(kallsyms_symbol_name(kallsyms, i))) continue; if (thisval <= addr && thisval > bestval) { best = i; bestval = thisval; } if (thisval > addr && thisval < nextval) nextval = thisval; } if (!best) return NULL; if (size) *size = nextval - bestval; if (offset) *offset = addr - bestval; return kallsyms_symbol_name(kallsyms, best); } void * __weak dereference_module_function_descriptor(struct module *mod, void *ptr) { return ptr; } /* * For kallsyms to ask for address resolution. NULL means not found. Careful * not to lock to avoid deadlock on oopses, simply disable preemption. */ const char *module_address_lookup(unsigned long addr, unsigned long *size, unsigned long *offset, char **modname, const unsigned char **modbuildid, char *namebuf) { const char *ret = NULL; struct module *mod; preempt_disable(); mod = __module_address(addr); if (mod) { if (modname) *modname = mod->name; if (modbuildid) { #if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) *modbuildid = mod->build_id; #else *modbuildid = NULL; #endif } ret = find_kallsyms_symbol(mod, addr, size, offset); } /* Make a copy in here where it's safe */ if (ret) { strncpy(namebuf, ret, KSYM_NAME_LEN - 1); ret = namebuf; } preempt_enable(); return ret; } int lookup_module_symbol_name(unsigned long addr, char *symname) { struct module *mod; preempt_disable(); list_for_each_entry_rcu(mod, &modules, list) { if (mod->state == MODULE_STATE_UNFORMED) continue; if (within_module(addr, mod)) { const char *sym; sym = find_kallsyms_symbol(mod, addr, NULL, NULL); if (!sym) goto out; strscpy(symname, sym, KSYM_NAME_LEN); preempt_enable(); return 0; } } out: preempt_enable(); return -ERANGE; } int lookup_module_symbol_attrs(unsigned long addr, unsigned long *size, unsigned long *offset, char *modname, char *name) { struct module *mod; preempt_disable(); list_for_each_entry_rcu(mod, &modules, list) { if (mod->state == MODULE_STATE_UNFORMED) continue; if (within_module(addr, mod)) { const char *sym; sym = find_kallsyms_symbol(mod, addr, size, offset); if (!sym) goto out; if (modname) strscpy(modname, mod->name, MODULE_NAME_LEN); if (name) strscpy(name, sym, KSYM_NAME_LEN); preempt_enable(); return 0; } } out: preempt_enable(); return -ERANGE; } int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type, char *name, char *module_name, int *exported) { struct module *mod; preempt_disable(); list_for_each_entry_rcu(mod, &modules, list) { struct mod_kallsyms *kallsyms; if (mod->state == MODULE_STATE_UNFORMED) continue; kallsyms = rcu_dereference_sched(mod->kallsyms); if (symnum < kallsyms->num_symtab) { const Elf_Sym *sym = &kallsyms->symtab[symnum]; *value = kallsyms_symbol_value(sym); *type = kallsyms->typetab[symnum]; strscpy(name, kallsyms_symbol_name(kallsyms, symnum), KSYM_NAME_LEN); strscpy(module_name, mod->name, MODULE_NAME_LEN); *exported = is_exported(name, *value, mod); preempt_enable(); return 0; } symnum -= kallsyms->num_symtab; } preempt_enable(); return -ERANGE; } /* Given a module and name of symbol, find and return the symbol's value */ unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name) { unsigned int i; struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms); for (i = 0; i < kallsyms->num_symtab; i++) { const Elf_Sym *sym = &kallsyms->symtab[i]; if (strcmp(name, kallsyms_symbol_name(kallsyms, i)) == 0 && sym->st_shndx != SHN_UNDEF) return kallsyms_symbol_value(sym); } return 0; } static unsigned long __module_kallsyms_lookup_name(const char *name) { struct module *mod; char *colon; colon = strnchr(name, MODULE_NAME_LEN, ':'); if (colon) { mod = find_module_all(name, colon - name, false); if (mod) return find_kallsyms_symbol_value(mod, colon + 1); return 0; } list_for_each_entry_rcu(mod, &modules, list) { unsigned long ret; if (mod->state == MODULE_STATE_UNFORMED) continue; ret = find_kallsyms_symbol_value(mod, name); if (ret) return ret; } return 0; } /* Look for this name: can be of form module:name. */ unsigned long module_kallsyms_lookup_name(const char *name) { unsigned long ret; /* Don't lock: we're in enough trouble already. */ preempt_disable(); ret = __module_kallsyms_lookup_name(name); preempt_enable(); return ret; } #ifdef CONFIG_LIVEPATCH int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *, unsigned long), void *data) { struct module *mod; unsigned int i; int ret = 0; mutex_lock(&module_mutex); list_for_each_entry(mod, &modules, list) { struct mod_kallsyms *kallsyms; if (mod->state == MODULE_STATE_UNFORMED) continue; /* Use rcu_dereference_sched() to remain compliant with the sparse tool */ preempt_disable(); kallsyms = rcu_dereference_sched(mod->kallsyms); preempt_enable(); for (i = 0; i < kallsyms->num_symtab; i++) { const Elf_Sym *sym = &kallsyms->symtab[i]; if (sym->st_shndx == SHN_UNDEF) continue; ret = fn(data, kallsyms_symbol_name(kallsyms, i), mod, kallsyms_symbol_value(sym)); if (ret != 0) goto out; } } out: mutex_unlock(&module_mutex); return ret; } #endif /* CONFIG_LIVEPATCH */