linux/kernel/module/kallsyms.c
Adrian Hunter 35adf9a4e5 modules: Fix corruption of /proc/kallsyms
The commit 91fb02f315 ("module: Move kallsyms support into a separate
file") changed from using strlcpy() to using strscpy() which created a
buffer overflow. That happened because:
 1) an incorrect value was passed as the buffer length
 2) strscpy() (unlike strlcpy()) may copy beyond the length of the
    input string when copying word-by-word.
The assumption was that because it was already known that the strings
being copied would fit in the space available, it was not necessary
to correctly set the buffer length.  strscpy() breaks that assumption
because although it will not touch bytes beyond the given buffer length
it may write bytes beyond the input string length when writing
word-by-word.

The result of the buffer overflow is to corrupt the symbol type
information that follows. e.g.

 $ sudo cat -v /proc/kallsyms | grep '\^' | head
 ffffffffc0615000 ^@ rfcomm_session_get  [rfcomm]
 ffffffffc061c060 ^@ session_list        [rfcomm]
 ffffffffc06150d0 ^@ rfcomm_send_frame   [rfcomm]
 ffffffffc0615130 ^@ rfcomm_make_uih     [rfcomm]
 ffffffffc07ed58d ^@ bnep_exit   [bnep]
 ffffffffc07ec000 ^@ bnep_rx_control     [bnep]
 ffffffffc07ec1a0 ^@ bnep_session        [bnep]
 ffffffffc07e7000 ^@ input_leds_event    [input_leds]
 ffffffffc07e9000 ^@ input_leds_handler  [input_leds]
 ffffffffc07e7010 ^@ input_leds_disconnect       [input_leds]

Notably, the null bytes (represented above by ^@) can confuse tools.

Fix by correcting the buffer length.

Fixes: 91fb02f315 ("module: Move kallsyms support into a separate file")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
2022-07-01 14:36:49 -07:00

522 lines
14 KiB
C

// 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;
preempt_disable();
/* The following is safe since this pointer cannot change */
rcu_dereference_sched(mod->kallsyms)->symtab = (void *)symsec->sh_addr;
rcu_dereference_sched(mod->kallsyms)->num_symtab = symsec->sh_size / sizeof(Elf_Sym);
/* Make sure we get permanent strtab: don't use info->strtab. */
rcu_dereference_sched(mod->kallsyms)->strtab =
(void *)info->sechdrs[info->index.str].sh_addr;
rcu_dereference_sched(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_sched(mod->kallsyms)->symtab;
for (ndst = i = 0; i < rcu_dereference_sched(mod->kallsyms)->num_symtab; i++) {
rcu_dereference_sched(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_sched(mod->kallsyms)->typetab[i];
dst[ndst] = src[i];
dst[ndst++].st_name = s - mod->core_kallsyms.strtab;
ret = strscpy(s,
&rcu_dereference_sched(mod->kallsyms)->strtab[src[i].st_name],
strtab_size);
if (ret < 0)
break;
s += ret + 1;
strtab_size -= ret + 1;
}
}
preempt_enable();
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;
}
/* Look for this name: can be of form module:name. */
unsigned long module_kallsyms_lookup_name(const char *name)
{
struct module *mod;
char *colon;
unsigned long ret = 0;
/* Don't lock: we're in enough trouble already. */
preempt_disable();
if ((colon = strnchr(name, MODULE_NAME_LEN, ':')) != NULL) {
if ((mod = find_module_all(name, colon - name, false)) != NULL)
ret = find_kallsyms_symbol_value(mod, colon + 1);
} else {
list_for_each_entry_rcu(mod, &modules, list) {
if (mod->state == MODULE_STATE_UNFORMED)
continue;
if ((ret = find_kallsyms_symbol_value(mod, name)) != 0)
break;
}
}
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 */