On Wed, Jul 26, 2023 at 04:12:23PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> Building with W=1 in some configurations produces a false positive
> warning for kallsyms:
>
> kernel/kallsyms.c: In function '__sprint_symbol.isra':
> kernel/kallsyms.c:503:17: error: 'strcpy' source argument is the same as destination [-Werror=restrict]
> 503 | strcpy(buffer, name);
> | ^~~~~~~~~~~~~~~~~~~~
>
> This originally showed up while building with -O3, but later started
> happening in other configurations as well, depending on inlining
> decisions. The underlying issue is that the local 'name' variable is
> always initialized to the be the same as 'buffer' in the called functions
> that fill the buffer, which gcc notices while inlining, though it could
> see that the address check always skips the copy.
>
> The calling conventions here are rather unusual, as all of the internal
> lookup functions (bpf_address_lookup, ftrace_mod_address_lookup,
> ftrace_func_address_lookup, module_address_lookup and
> kallsyms_lookup_buildid) already use the provided buffer and either return
> the address of that buffer to indicate success, or NULL for failure,
> but the callers are written to also expect an arbitrary other buffer
> to be returned.
>
> Rework the calling conventions to return the length of the filled buffer
> instead of its address, which is simpler and easier to follow as well
> as avoiding the warning. Leave only the kallsyms_lookup() calling conventions
> unchanged, since that is called from 16 different functions and
> adapting this would be a much bigger change.
>
> Link: https://lore.kernel.org/all/20200107214042.855757-1-arnd@arndb.de/
> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> v3: use strscpy() instead of strlcpy()
Thank you! :) (Though see my notes below...)
> [...]
> @@ -344,13 +345,12 @@ const char *module_address_lookup(unsigned long addr,
> #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);
This -1 was to keep the buffer NUL-terminated.
> - ret = namebuf;
> + sym = find_kallsyms_symbol(mod, addr, size, offset);
> +
> + if (sym)
> + ret = strscpy(namebuf, sym, KSYM_NAME_LEN - 1);
This strscpy should use KSYM_NAME_LEN without the "- 1".
> }
> +
> preempt_enable();
>
-Kees
@@ -1130,17 +1130,17 @@ static inline bool bpf_jit_kallsyms_enabled(void)
return false;
}
-const char *__bpf_address_lookup(unsigned long addr, unsigned long *size,
+int __bpf_address_lookup(unsigned long addr, unsigned long *size,
unsigned long *off, char *sym);
bool is_bpf_text_address(unsigned long addr);
int bpf_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
char *sym);
-static inline const char *
+static inline int
bpf_address_lookup(unsigned long addr, unsigned long *size,
unsigned long *off, char **modname, char *sym)
{
- const char *ret = __bpf_address_lookup(addr, size, off, sym);
+ int ret = __bpf_address_lookup(addr, size, off, sym);
if (ret && modname)
*modname = NULL;
@@ -1184,11 +1184,11 @@ static inline bool bpf_jit_kallsyms_enabled(void)
return false;
}
-static inline const char *
+static inline int
__bpf_address_lookup(unsigned long addr, unsigned long *size,
unsigned long *off, char *sym)
{
- return NULL;
+ return 0;
}
static inline bool is_bpf_text_address(unsigned long addr)
@@ -1202,11 +1202,11 @@ static inline int bpf_get_kallsym(unsigned int symnum, unsigned long *value,
return -ERANGE;
}
-static inline const char *
+static inline int
bpf_address_lookup(unsigned long addr, unsigned long *size,
unsigned long *off, char **modname, char *sym)
{
- return NULL;
+ return 0;
}
static inline void bpf_prog_kallsyms_add(struct bpf_prog *fp)
@@ -87,15 +87,15 @@ struct ftrace_direct_func;
#if defined(CONFIG_FUNCTION_TRACER) && defined(CONFIG_MODULES) && \
defined(CONFIG_DYNAMIC_FTRACE)
-const char *
+int
ftrace_mod_address_lookup(unsigned long addr, unsigned long *size,
unsigned long *off, char **modname, char *sym);
#else
-static inline const char *
+static inline int
ftrace_mod_address_lookup(unsigned long addr, unsigned long *size,
unsigned long *off, char **modname, char *sym)
{
- return NULL;
+ return 0;
}
#endif
@@ -920,11 +920,11 @@ int module_kallsyms_on_each_symbol(const char *modname,
* least KSYM_NAME_LEN long: a pointer to namebuf is returned if
* found, otherwise NULL.
*/
-const char *module_address_lookup(unsigned long addr,
- unsigned long *symbolsize,
- unsigned long *offset,
- char **modname, const unsigned char **modbuildid,
- char *namebuf);
+int module_address_lookup(unsigned long addr,
+ unsigned long *symbolsize,
+ unsigned long *offset,
+ char **modname, const unsigned char **modbuildid,
+ char *namebuf);
int lookup_module_symbol_name(unsigned long addr, char *symname);
int lookup_module_symbol_attrs(unsigned long addr,
unsigned long *size,
@@ -953,14 +953,14 @@ static inline int module_kallsyms_on_each_symbol(const char *modname,
}
/* For kallsyms to ask for address resolution. NULL means not found. */
-static inline const char *module_address_lookup(unsigned long addr,
+static inline int module_address_lookup(unsigned long addr,
unsigned long *symbolsize,
unsigned long *offset,
char **modname,
const unsigned char **modbuildid,
char *namebuf)
{
- return NULL;
+ return 0;
}
static inline int lookup_module_symbol_name(unsigned long addr, char *symname)
@@ -687,11 +687,11 @@ static struct bpf_ksym *bpf_ksym_find(unsigned long addr)
return n ? container_of(n, struct bpf_ksym, tnode) : NULL;
}
-const char *__bpf_address_lookup(unsigned long addr, unsigned long *size,
+int __bpf_address_lookup(unsigned long addr, unsigned long *size,
unsigned long *off, char *sym)
{
struct bpf_ksym *ksym;
- char *ret = NULL;
+ int ret = 0;
rcu_read_lock();
ksym = bpf_ksym_find(addr);
@@ -699,9 +699,8 @@ const char *__bpf_address_lookup(unsigned long addr, unsigned long *size,
unsigned long symbol_start = ksym->start;
unsigned long symbol_end = ksym->end;
- strncpy(sym, ksym->name, KSYM_NAME_LEN);
+ ret = strscpy(sym, ksym->name, KSYM_NAME_LEN);
- ret = sym;
if (size)
*size = symbol_end - symbol_start;
if (off)
@@ -399,12 +399,12 @@ int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
!!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
}
-static const char *kallsyms_lookup_buildid(unsigned long addr,
+static int kallsyms_lookup_buildid(unsigned long addr,
unsigned long *symbolsize,
unsigned long *offset, char **modname,
const unsigned char **modbuildid, char *namebuf)
{
- const char *ret;
+ int ret;
namebuf[KSYM_NAME_LEN - 1] = 0;
namebuf[0] = 0;
@@ -421,7 +421,7 @@ static const char *kallsyms_lookup_buildid(unsigned long addr,
if (modbuildid)
*modbuildid = NULL;
- ret = namebuf;
+ ret = strlen(namebuf);
goto found;
}
@@ -453,8 +453,13 @@ const char *kallsyms_lookup(unsigned long addr,
unsigned long *offset,
char **modname, char *namebuf)
{
- return kallsyms_lookup_buildid(addr, symbolsize, offset, modname,
- NULL, 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)
@@ -489,19 +494,15 @@ static int __sprint_symbol(char *buffer, unsigned long address,
{
char *modname;
const unsigned char *buildid;
- const char *name;
unsigned long offset, size;
int len;
address += symbol_offset;
- name = kallsyms_lookup_buildid(address, &size, &offset, &modname, &buildid,
+ len = kallsyms_lookup_buildid(address, &size, &offset, &modname, &buildid,
buffer);
- if (!name)
+ if (!len)
return sprintf(buffer, "0x%lx", address - symbol_offset);
- if (name != buffer)
- strcpy(buffer, name);
- len = strlen(buffer);
offset -= symbol_offset;
if (add_offset)
@@ -321,14 +321,15 @@ void * __weak dereference_module_function_descriptor(struct module *mod,
* 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)
+int module_address_lookup(unsigned long addr,
+ unsigned long *size,
+ unsigned long *offset,
+ char **modname,
+ const unsigned char **modbuildid,
+ char *namebuf)
{
- const char *ret = NULL;
+ const char *sym;
+ int ret = 0;
struct module *mod;
preempt_disable();
@@ -344,13 +345,12 @@ const char *module_address_lookup(unsigned long addr,
#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;
+ sym = find_kallsyms_symbol(mod, addr, size, offset);
+
+ if (sym)
+ ret = strscpy(namebuf, sym, KSYM_NAME_LEN - 1);
}
+
preempt_enable();
return ret;
@@ -6965,7 +6965,7 @@ allocate_ftrace_mod_map(struct module *mod,
return mod_map;
}
-static const char *
+static int
ftrace_func_address_lookup(struct ftrace_mod_map *mod_map,
unsigned long addr, unsigned long *size,
unsigned long *off, char *sym)
@@ -6986,21 +6986,18 @@ ftrace_func_address_lookup(struct ftrace_mod_map *mod_map,
*size = found_func->size;
if (off)
*off = addr - found_func->ip;
- if (sym)
- strscpy(sym, found_func->name, KSYM_NAME_LEN);
-
- return found_func->name;
+ return strscpy(sym, found_func->name, KSYM_NAME_LEN);
}
- return NULL;
+ return 0;
}
-const char *
+int
ftrace_mod_address_lookup(unsigned long addr, unsigned long *size,
unsigned long *off, char **modname, char *sym)
{
struct ftrace_mod_map *mod_map;
- const char *ret = NULL;
+ int ret;
/* mod_map is freed via call_rcu() */
preempt_disable();