Re: [PATCH v3 06/13] mm/execmem: introduce execmem_data_alloc()

[Song Liu]

On Mon, Sep 18, 2023 at 12:31 AM Mike Rapoport <rppt@xxxxxxxxxx> wrote:
>
[...]
> diff --git a/include/linux/execmem.h b/include/linux/execmem.h
> index 519bdfdca595..09d45ac786e9 100644
> --- a/include/linux/execmem.h
> +++ b/include/linux/execmem.h
> @@ -29,6 +29,7 @@
>   * @EXECMEM_KPROBES: parameters for kprobes
>   * @EXECMEM_FTRACE: parameters for ftrace
>   * @EXECMEM_BPF: parameters for BPF
> + * @EXECMEM_MODULE_DATA: parameters for module data sections
>   * @EXECMEM_TYPE_MAX:
>   */
>  enum execmem_type {
> @@ -37,6 +38,7 @@ enum execmem_type {
>         EXECMEM_KPROBES,
>         EXECMEM_FTRACE,

In longer term, I think we can improve the JITed code and merge
kprobe/ftrace/bpf. to use the same ranges. Also, do we need special
setting for FTRACE? If not, let's just remove it.

>         EXECMEM_BPF,
> +       EXECMEM_MODULE_DATA,
>         EXECMEM_TYPE_MAX,
>  };

Overall, it is great that kprobe/ftrace/bpf no longer depend on modules.

OTOH, I think we should merge execmem_type and existing mod_mem_type.
Otherwise, we still need to handle page permissions in multiple places.
What is our plan for that?

Thanks,
Song


>
> @@ -107,6 +109,23 @@ struct execmem_params *execmem_arch_params(void);
>   */
>  void *execmem_text_alloc(enum execmem_type type, size_t size);
>
> +/**
> + * execmem_data_alloc - allocate memory for data coupled to code
> + * @type: type of the allocation
> + * @size: how many bytes of memory are required
> + *
> + * Allocates memory that will contain data coupled with executable code,
> + * like data sections in kernel modules.
> + *
> + * The memory will have protections defined by architecture.
> + *
> + * The allocated memory will reside in an area that does not impose
> + * restrictions on the addressing modes.
> + *
> + * Return: a pointer to the allocated memory or %NULL
> + */
> +void *execmem_data_alloc(enum execmem_type type, size_t size);
> +
>  /**
>   * execmem_free - free executable memory
>   * @ptr: pointer to the memory that should be freed
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index c4146bfcd0a7..2ae83a6abf66 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -1188,25 +1188,16 @@ void __weak module_arch_freeing_init(struct module *mod)
>  {
>  }
>
> -static bool mod_mem_use_vmalloc(enum mod_mem_type type)
> -{
> -       return IS_ENABLED(CONFIG_ARCH_WANTS_MODULES_DATA_IN_VMALLOC) &&
> -               mod_mem_type_is_core_data(type);
> -}
> -
>  static void *module_memory_alloc(unsigned int size, enum mod_mem_type type)
>  {
> -       if (mod_mem_use_vmalloc(type))
> -               return vzalloc(size);
> +       if (mod_mem_type_is_data(type))
> +               return execmem_data_alloc(EXECMEM_MODULE_DATA, size);
>         return execmem_text_alloc(EXECMEM_MODULE_TEXT, size);
>  }
>
>  static void module_memory_free(void *ptr, enum mod_mem_type type)
>  {
> -       if (mod_mem_use_vmalloc(type))
> -               vfree(ptr);
> -       else
> -               execmem_free(ptr);
> +       execmem_free(ptr);
>  }
>
>  static void free_mod_mem(struct module *mod)
> diff --git a/mm/execmem.c b/mm/execmem.c
> index abcbd07e05ac..aeff85261360 100644
> --- a/mm/execmem.c
> +++ b/mm/execmem.c
> @@ -53,11 +53,23 @@ static void *execmem_alloc(size_t size, struct execmem_range *range)
>         return kasan_reset_tag(p);
>  }
>
> +static inline bool execmem_range_is_data(enum execmem_type type)
> +{
> +       return type == EXECMEM_MODULE_DATA;
> +}
> +
>  void *execmem_text_alloc(enum execmem_type type, size_t size)
>  {
>         return execmem_alloc(size, &execmem_params.ranges[type]);
>  }
>
> +void *execmem_data_alloc(enum execmem_type type, size_t size)
> +{
> +       WARN_ON_ONCE(!execmem_range_is_data(type));
> +
> +       return execmem_alloc(size, &execmem_params.ranges[type]);
> +}
> +
>  void execmem_free(void *ptr)
>  {
>         /*
> @@ -93,7 +105,10 @@ static void execmem_init_missing(struct execmem_params *p)
>                 struct execmem_range *r = &p->ranges[i];
>
>                 if (!r->start) {
> -                       r->pgprot = default_range->pgprot;
> +                       if (execmem_range_is_data(i))
> +                               r->pgprot = PAGE_KERNEL;
> +                       else
> +                               r->pgprot = default_range->pgprot;
>                         r->alignment = default_range->alignment;
>                         r->start = default_range->start;
>                         r->end = default_range->end;
> --
> 2.39.2
>