Re: [PATCH v2 04/12] mm/execmem, arch: convert remaining overrides of module_alloc to execmem

[Edgecombe, Rick P]

On Fri, 2023-06-16 at 11:50 +0300, Mike Rapoport wrote:
> -void *module_alloc(unsigned long size)
> -{
> -       gfp_t gfp_mask = GFP_KERNEL;
> -       void *p;
> -
> -       if (PAGE_ALIGN(size) > MODULES_LEN)
> -               return NULL;
> +static struct execmem_params execmem_params = {
> +       .modules = {
> +               .flags = EXECMEM_KASAN_SHADOW,
> +               .text = {
> +                       .alignment = MODULE_ALIGN,
> +               },
> +       },
> +};

Did you consider making these execmem_params's ro_after_init? Not that
it is security sensitive, but it's a nice hint to the reader that it is
only modified at init. And I guess basically free sanitizing of buggy
writes to it.

>  
> -       p = __vmalloc_node_range(size, MODULE_ALIGN,
> -                                MODULES_VADDR +
> get_module_load_offset(),
> -                                MODULES_END, gfp_mask, PAGE_KERNEL,
> -                                VM_FLUSH_RESET_PERMS |
> VM_DEFER_KMEMLEAK,
> -                                NUMA_NO_NODE,
> __builtin_return_address(0));
> +struct execmem_params __init *execmem_arch_params(void)
> +{
> +       unsigned long start = MODULES_VADDR +
> get_module_load_offset();

I think we can drop the mutex's in get_module_load_offset() now, since
execmem_arch_params() should only be called once at init.

>  
> -       if (p && (kasan_alloc_module_shadow(p, size, gfp_mask) < 0))
> {
> -               vfree(p);
> -               return NULL;
> -       }
> +       execmem_params.modules.text.start = start;
> +       execmem_params.modules.text.end = MODULES_END;
> +       execmem_params.modules.text.pgprot = PAGE_KERNEL;
>  
> -       return p;
> +       return &execmem_params;
>  }
>