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

[Song Liu]

On Fri, Jun 16, 2023 at 1:51 AM Mike Rapoport <rppt@xxxxxxxxxx> wrote:
[...]
> diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
> index 5af4975caeb5..c3d999f3a3dd 100644
> --- a/arch/arm64/kernel/module.c
> +++ b/arch/arm64/kernel/module.c
> @@ -17,56 +17,50 @@
>  #include <linux/moduleloader.h>
>  #include <linux/scs.h>
>  #include <linux/vmalloc.h>
> +#include <linux/execmem.h>
>  #include <asm/alternative.h>
>  #include <asm/insn.h>
>  #include <asm/scs.h>
>  #include <asm/sections.h>
>
> -void *module_alloc(unsigned long size)
> +static struct execmem_params execmem_params = {
> +       .modules = {
> +               .flags = EXECMEM_KASAN_SHADOW,
> +               .text = {
> +                       .alignment = MODULE_ALIGN,
> +               },
> +       },
> +};
> +
> +struct execmem_params __init *execmem_arch_params(void)
>  {
>         u64 module_alloc_end = module_alloc_base + MODULES_VSIZE;
> -       gfp_t gfp_mask = GFP_KERNEL;
> -       void *p;
> -
> -       /* Silence the initial allocation */
> -       if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS))
> -               gfp_mask |= __GFP_NOWARN;
>
> -       if (IS_ENABLED(CONFIG_KASAN_GENERIC) ||
> -           IS_ENABLED(CONFIG_KASAN_SW_TAGS))
> -               /* don't exceed the static module region - see below */
> -               module_alloc_end = MODULES_END;
> +       execmem_params.modules.text.pgprot = PAGE_KERNEL;
> +       execmem_params.modules.text.start = module_alloc_base;

I think I mentioned this earlier. For arm64 with CONFIG_RANDOMIZE_BASE,
module_alloc_base is not yet set when execmem_arch_params() is
called. So we will need some extra logic for this.

Thanks,
Song


> +       execmem_params.modules.text.end = module_alloc_end;
>
> -       p = __vmalloc_node_range(size, MODULE_ALIGN, module_alloc_base,
> -                               module_alloc_end, gfp_mask, PAGE_KERNEL, VM_DEFER_KMEMLEAK,
> -                               NUMA_NO_NODE, __builtin_return_address(0));
> -
> -       if (!p && IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
> +       /*
> +        * KASAN without KASAN_VMALLOC can only deal with module
> +        * allocations being served from the reserved module region,
> +        * since the remainder of the vmalloc region is already
> +        * backed by zero shadow pages, and punching holes into it
> +        * is non-trivial. Since the module region is not randomized
> +        * when KASAN is enabled without KASAN_VMALLOC, it is even
> +        * less likely that the module region gets exhausted, so we
> +        * can simply omit this fallback in that case.
> +        */
> +       if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
>             (IS_ENABLED(CONFIG_KASAN_VMALLOC) ||
>              (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
> -             !IS_ENABLED(CONFIG_KASAN_SW_TAGS))))
> -               /*
> -                * KASAN without KASAN_VMALLOC can only deal with module
> -                * allocations being served from the reserved module region,
> -                * since the remainder of the vmalloc region is already
> -                * backed by zero shadow pages, and punching holes into it
> -                * is non-trivial. Since the module region is not randomized
> -                * when KASAN is enabled without KASAN_VMALLOC, it is even
> -                * less likely that the module region gets exhausted, so we
> -                * can simply omit this fallback in that case.
> -                */
> -               p = __vmalloc_node_range(size, MODULE_ALIGN, module_alloc_base,
> -                               module_alloc_base + SZ_2G, GFP_KERNEL,
> -                               PAGE_KERNEL, 0, NUMA_NO_NODE,
> -                               __builtin_return_address(0));
> -
> -       if (p && (kasan_alloc_module_shadow(p, size, gfp_mask) < 0)) {
> -               vfree(p);
> -               return NULL;
> +             !IS_ENABLED(CONFIG_KASAN_SW_TAGS)))) {
> +               unsigned long end = module_alloc_base + SZ_2G;
> +
> +               execmem_params.modules.text.fallback_start = module_alloc_base;
> +               execmem_params.modules.text.fallback_end = end;
>         }
>
> -       /* Memory is intended to be executable, reset the pointer tag. */
> -       return kasan_reset_tag(p);
> +       return &execmem_params;
>  }
>
>  enum aarch64_reloc_op {