From 7e1f4eb9a60d40dd17a97d9b76818682a024a127 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Thu, 4 Apr 2024 12:04:54 +0200 Subject: [PATCH] kallsyms: rework symbol lookup return codes 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/lkml/20200107214042.855757-1-arnd@arndb.de/ Link: https://lore.kernel.org/lkml/20240326130647.7bfb1d92@gandalf.local.home/ Tested-by: Geert Uytterhoeven Reviewed-by: Luis Chamberlain Acked-by: Steven Rostedt (Google) Signed-off-by: Arnd Bergmann --- include/linux/filter.h | 14 +++++++------- include/linux/ftrace.h | 6 +++--- include/linux/module.h | 14 +++++++------- kernel/bpf/core.c | 7 +++---- kernel/kallsyms.c | 23 ++++++++++++----------- kernel/module/kallsyms.c | 25 ++++++++++++------------- kernel/trace/ftrace.c | 13 +++++-------- 7 files changed, 49 insertions(+), 53 deletions(-) diff --git a/include/linux/filter.h b/include/linux/filter.h index 0f12cf01070e..5669da513cd7 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -1208,18 +1208,18 @@ 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); struct bpf_prog *bpf_prog_ksym_find(unsigned long addr); -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; @@ -1263,11 +1263,11 @@ 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) @@ -1286,11 +1286,11 @@ static inline struct bpf_prog *bpf_prog_ksym_find(unsigned long addr) return NULL; } -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) diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h index 800995c425e0..b792274189a3 100644 --- a/include/linux/ftrace.h +++ b/include/linux/ftrace.h @@ -86,15 +86,15 @@ struct ftrace_hash; #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 diff --git a/include/linux/module.h b/include/linux/module.h index ffa1c603163c..330ffb59efe5 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -931,11 +931,11 @@ 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, @@ -964,14 +964,14 @@ 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) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 1a6c3faa6e4a..695a0fb2cd4d 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -736,11 +736,11 @@ 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); @@ -748,9 +748,8 @@ const char *__bpf_address_lookup(unsigned long addr, unsigned long *size, unsigned long symbol_start = ksym->start; unsigned long symbol_end = ksym->end; - strscpy(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) diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index 22ea19a36e6e..98b9622d372e 100644 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -388,12 +388,12 @@ 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; @@ -410,7 +410,7 @@ static const char *kallsyms_lookup_buildid(unsigned long addr, if (modbuildid) *modbuildid = NULL; - ret = namebuf; + ret = strlen(namebuf); goto found; } @@ -442,8 +442,13 @@ 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) @@ -478,19 +483,15 @@ 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) diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c index 62fb57bb9f16..bf65e0c3c86f 100644 --- a/kernel/module/kallsyms.c +++ b/kernel/module/kallsyms.c @@ -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(); @@ -344,12 +345,10 @@ 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) { - strscpy(namebuf, ret, KSYM_NAME_LEN); - ret = namebuf; + sym = find_kallsyms_symbol(mod, addr, size, offset); + + if (sym) + ret = strscpy(namebuf, sym, KSYM_NAME_LEN); } preempt_enable(); diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 65208d3b5ed9..eacab4020508 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -6969,7 +6969,7 @@ 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) @@ -6990,21 +6990,18 @@ 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 = 0; /* mod_map is freed via call_rcu() */ preempt_disable();