Re: [PATCH v5 09/13] module: Move kallsyms support into a separate file

[Christophe Leroy]

Le 09/02/2022 à 18:08, Aaron Tomlin a écrit :
> No functional change.
> 
> This patch migrates kallsyms code out of core module
> code kernel/module/kallsyms.c
> 
> Signed-off-by: Aaron Tomlin <atomlin@xxxxxxxxxx>
> ---
>   kernel/module/Makefile   |   1 +
>   kernel/module/internal.h |  27 ++
>   kernel/module/kallsyms.c | 502 +++++++++++++++++++++++++++++++++++++
>   kernel/module/main.c     | 518 +--------------------------------------
>   4 files changed, 534 insertions(+), 514 deletions(-)
>   create mode 100644 kernel/module/kallsyms.c

Checkpatch reports:

total: 3 errors, 1 warnings, 26 checks, 1103 lines checked


Sparse reports the following:

   CHECK   kernel/module/kallsyms.c
kernel/module/kallsyms.c:174:23: warning: incorrect type in assignment 
(different address spaces)
kernel/module/kallsyms.c:174:23:    expected struct mod_kallsyms 
[noderef] __rcu *kallsyms
kernel/module/kallsyms.c:174:23:    got void *
kernel/module/kallsyms.c:176:12: warning: dereference of noderef expression
kernel/module/kallsyms.c:177:12: warning: dereference of noderef expression
kernel/module/kallsyms.c:179:12: warning: dereference of noderef expression
kernel/module/kallsyms.c:180:12: warning: dereference of noderef expression
kernel/module/kallsyms.c:189:18: warning: dereference of noderef expression
kernel/module/kallsyms.c:190:35: warning: dereference of noderef expression
kernel/module/kallsyms.c:191:20: warning: dereference of noderef expression
kernel/module/kallsyms.c:196:32: warning: dereference of noderef expression
kernel/module/kallsyms.c:199:45: warning: dereference of noderef expression



> 
> diff --git a/kernel/module/Makefile b/kernel/module/Makefile
> index 62c9fc91d411..868b13c06920 100644
> --- a/kernel/module/Makefile
> +++ b/kernel/module/Makefile
> @@ -12,4 +12,5 @@ obj-$(CONFIG_LIVEPATCH) += livepatch.o
>   obj-$(CONFIG_MODULES_TREE_LOOKUP) += tree_lookup.o
>   obj-$(CONFIG_STRICT_MODULE_RWX) += strict_rwx.o
>   obj-$(CONFIG_DEBUG_KMEMLEAK) += debug_kmemleak.o
> +obj-$(CONFIG_KALLSYMS) += kallsyms.o
>   endif
> diff --git a/kernel/module/internal.h b/kernel/module/internal.h
> index 33d7befd0602..7973666452c3 100644
> --- a/kernel/module/internal.h
> +++ b/kernel/module/internal.h
> @@ -69,6 +69,11 @@ struct load_info {
>   };
>   
>   int mod_verify_sig(const void *mod, struct load_info *info);
> +struct module *find_module_all(const char *name, size_t len, bool even_unformed);
> +unsigned long kernel_symbol_value(const struct kernel_symbol *sym);

This function is small enought to be a 'static inline' in internal.h

> +int cmp_name(const void *name, const void *sym);
> +long get_offset(struct module *mod, unsigned int *size, Elf_Shdr *sechdr,
> +		       unsigned int section);

Having a non static function called get_offset() seems dangerous.

There are already several get_offset() functions in the kernel allthough 
they are all static.

It takes a struct module as an argument so it could be called 
module_get_offset()


>   
>   #ifdef CONFIG_LIVEPATCH
>   int copy_module_elf(struct module *mod, struct load_info *info);
> @@ -178,3 +183,25 @@ void kmemleak_load_module(const struct module *mod, const struct load_info *info
>   static inline void __maybe_unused kmemleak_load_module(const struct module *mod,
>   						       const struct load_info *info) { }
>   #endif /* CONFIG_DEBUG_KMEMLEAK */
> +
> +#ifdef CONFIG_KALLSYMS
> +#ifdef CONFIG_STACKTRACE_BUILD_ID
> +void init_build_id(struct module *mod, const struct load_info *info);
> +#else /* !CONFIG_STACKTRACE_BUILD_ID */
> +static inline void init_build_id(struct module *mod, const struct load_info *info) { }
> +
> +#endif
> +void layout_symtab(struct module *mod, struct load_info *info);
> +void add_kallsyms(struct module *mod, const struct load_info *info);
> +bool sect_empty(const Elf_Shdr *sect);

sect_empty() is small enough to remain a static inline.

> +const char *find_kallsyms_symbol(struct module *mod, unsigned long addr,
> +					unsigned long *size, unsigned long *offset);

This is not used outside kallsyms.c, no need to have it in internal.h

> +#else /* !CONFIG_KALLSYMS */
> +static inline void layout_symtab(struct module *mod, struct load_info *info) { }
> +static inline void add_kallsyms(struct module *mod, const struct load_info *info) { }
> +static inline char *find_kallsyms_symbol(struct module *mod, unsigned long addr,
> +					 unsigned long *size, unsigned long *offset)

This is not used outside kallsyms.c, no need to have it when 
!CONFIG_KALLSYMS

> +{
> +	return NULL;
> +}
> +#endif /* CONFIG_KALLSYMS */
> diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
> new file mode 100644
> index 000000000000..ed28f6310701
> --- /dev/null
> +++ b/kernel/module/kallsyms.c
> @@ -0,0 +1,502 @@
...
> +
> +/* Given a module and name of symbol, find and return the symbol's value */
> +static unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name)

This function is called from main.c, it can't be static and must be 
defined in internal.h

> +{
> +	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;
> +}
> +
...
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index c9931479e2eb..378dd7fd1b6a 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -285,7 +285,7 @@ static bool check_exported_symbol(const struct symsearch *syms,
>   	return true;
>   }
>   
> -static unsigned long kernel_symbol_value(const struct kernel_symbol *sym)
> +unsigned long kernel_symbol_value(const struct kernel_symbol *sym)

This function is small enought to become a 'static inline' in internal.h

>   {
>   #ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
>   	return (unsigned long)offset_to_ptr(&sym->value_offset);
> @@ -314,7 +314,7 @@ static const char *kernel_symbol_namespace(const struct kernel_symbol *sym)
>   #endif
>   }
>   
> -static int cmp_name(const void *name, const void *sym)
> +int cmp_name(const void *name, const void *sym)

This function is small enought to become a 'static inline' in internal.h

>   {
>   	return strcmp(name, kernel_symbol_name(sym));
>   }
> @@ -384,7 +384,7 @@ static bool find_symbol(struct find_symbol_arg *fsa)
>    * Search for module by name: must hold module_mutex (or preempt disabled
>    * for read-only access).
>    */
> -static struct module *find_module_all(const char *name, size_t len,
> +struct module *find_module_all(const char *name, size_t len,
>   				      bool even_unformed)
>   {
>   	struct module *mod;
> @@ -1291,13 +1291,6 @@ resolve_symbol_wait(struct module *mod,
>   	return ksym;
>   }
>   
> -#ifdef CONFIG_KALLSYMS
> -static inline bool sect_empty(const Elf_Shdr *sect)
> -{
> -	return !(sect->sh_flags & SHF_ALLOC) || sect->sh_size == 0;
> -}
> -#endif
> -
>   /*
>    * /sys/module/foo/sections stuff
>    * J. Corbet <corbet@xxxxxxx>
> @@ -2061,7 +2054,7 @@ unsigned int __weak arch_mod_section_prepend(struct module *mod,
>   }
>   
>   /* Update size with this section: return offset. */
> -static long get_offset(struct module *mod, unsigned int *size,
> +long get_offset(struct module *mod, unsigned int *size,
>   		       Elf_Shdr *sechdr, unsigned int section)
>   {
>   	long ret;
> @@ -2263,228 +2256,6 @@ static void free_modinfo(struct module *mod)
>   	}
>   }
>   
...