Re: [PATCH v14 3/9] powerpc/modules: Make module_alloc() Strict Module RWX aware

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 17/05/2021 à 05:28, Jordan Niethe a écrit :
> Make module_alloc() use PAGE_KERNEL protections instead of
> PAGE_KERNEL_EXEX if Strict Module RWX is enabled.
> 
> Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> ---
> v14: - Split out from powerpc: Set ARCH_HAS_STRICT_MODULE_RWX
>       - Add and use strict_module_rwx_enabled() helper
> ---
>   arch/powerpc/include/asm/mmu.h | 5 +++++
>   arch/powerpc/kernel/module.c   | 4 +++-
>   2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
> index 607168b1aef4..7710bf0cbf8a 100644
> --- a/arch/powerpc/include/asm/mmu.h
> +++ b/arch/powerpc/include/asm/mmu.h
> @@ -357,6 +357,11 @@ static inline bool strict_kernel_rwx_enabled(void)
>   	return false;
>   }
>   #endif
> +
> +static inline bool strict_module_rwx_enabled(void)
> +{
> +	return IS_ENABLED(CONFIG_STRICT_MODULE_RWX) && strict_kernel_rwx_enabled();
> +}

Looking at arch/Kconfig, I have the feeling that it is possible to select CONFIG_STRICT_MODULE_RWX 
without selecting CONFIG_STRICT_KERNEL_RWX.

In that case, strict_kernel_rwx_enabled() will return false.

>   #endif /* !__ASSEMBLY__ */
>   
>   /* The kernel use the constants below to index in the page sizes array.
> diff --git a/arch/powerpc/kernel/module.c b/arch/powerpc/kernel/module.c
> index 3f35c8d20be7..ed04a3ba66fe 100644
> --- a/arch/powerpc/kernel/module.c
> +++ b/arch/powerpc/kernel/module.c
> @@ -92,12 +92,14 @@ int module_finalize(const Elf_Ehdr *hdr,
>   static __always_inline void *
>   __module_alloc(unsigned long size, unsigned long start, unsigned long end)
>   {
> +	pgprot_t prot = strict_module_rwx_enabled() ? PAGE_KERNEL : PAGE_KERNEL_EXEC;
> +
>   	/*
>   	 * Don't do huge page allocations for modules yet until more testing
>   	 * is done. STRICT_MODULE_RWX may require extra work to support this
>   	 * too.
>   	 */
> -	return __vmalloc_node_range(size, 1, start, end, GFP_KERNEL, PAGE_KERNEL_EXEC,
> +	return __vmalloc_node_range(size, 1, start, end, GFP_KERNEL, prot,
>   				    VM_FLUSH_RESET_PERMS | VM_NO_HUGE_VMAP,
>   				    NUMA_NO_NODE, __builtin_return_address(0));
>   }
>