Re: [PATCH v4 20/24] crypto: x86/ciphers - load based on CPU features

[Jason A. Donenfeld]

On Tue, Nov 15, 2022 at 10:13:38PM -0600, Robert Elliott wrote:
> diff --git a/arch/x86/crypto/curve25519-x86_64.c b/arch/x86/crypto/curve25519-x86_64.c
> index d55fa9e9b9e6..ae7536b17bf9 100644
> --- a/arch/x86/crypto/curve25519-x86_64.c
> +++ b/arch/x86/crypto/curve25519-x86_64.c
> @@ -12,7 +12,7 @@
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/scatterlist.h>
> -
> +#include <asm/cpu_device_id.h>
>  #include <asm/cpufeature.h>
>  #include <asm/processor.h>
>  
> @@ -1697,13 +1697,22 @@ static struct kpp_alg curve25519_alg = {
>  	.max_size		= curve25519_max_size,
>  };
>  
> +static const struct x86_cpu_id module_cpu_ids[] = {
> +	X86_MATCH_FEATURE(X86_FEATURE_ADX, NULL),
> +	{}
> +};
> +MODULE_DEVICE_TABLE(x86cpu, module_cpu_ids);
>  
>  static int __init curve25519_mod_init(void)
>  {
> -	if (boot_cpu_has(X86_FEATURE_BMI2) && boot_cpu_has(X86_FEATURE_ADX))
> -		static_branch_enable(&curve25519_use_bmi2_adx);
> -	else
> -		return 0;
> +	if (!x86_match_cpu(module_cpu_ids))
> +		return -ENODEV;
> +
> +	if (!boot_cpu_has(X86_FEATURE_BMI2))
> +		return -ENODEV;
> +
> +	static_branch_enable(&curve25519_use_bmi2_adx);

Can the user still insmod this? If so, you can't remove the ADX check.
Ditto for rest of patch.