Subject: Re: [PATCH] arm64: cpufeature: Don't expose ZFR0 to userspace when SVE is not enabled

From: Dave Martin <[email-masked]>
Date: Mon, 14 Oct 2019 15:41:07 +0100

On Mon, Oct 14, 2019 at 11:21:13AM +0100, Julien Grall wrote:
> The kernel may not support SVE if CONFIG_ARM64_SVE is not set and
> will hide the feature from the from userspace.
> 
> Unfortunately, the fields of ID_AA64ZFR0_EL1 are still exposed and could
> lead to undefined behavior in userspace.
> 
> The kernel should not used the register when CONFIG_SVE is disabled.
> Therefore, we only need to hidden them from the userspace.
> 
> Signed-off-by: Julien Grall <[email-masked]>
> Fixes: 06a916feca2b ('arm64: Expose SVE2 features for userspace')

Reviewed-by: Dave Martin <[email-masked]>

> ---
>  arch/arm64/kernel/cpufeature.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index cabebf1a7976..80f459ad0190 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -176,11 +176,16 @@ static const struct arm64_ftr_bits ftr_id_aa64pfr1[] = {
>  };
>  
>  static const struct arm64_ftr_bits ftr_id_aa64zfr0[] = {
> -	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ZFR0_SM4_SHIFT, 4, 0),
> -	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ZFR0_SHA3_SHIFT, 4, 0),
> -	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ZFR0_BITPERM_SHIFT, 4, 0),
> -	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ZFR0_AES_SHIFT, 4, 0),
> -	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ZFR0_SVEVER_SHIFT, 4, 0),
> +	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_SVE),
> +		       FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ZFR0_SM4_SHIFT, 4, 0),
> +	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_SVE),
> +		       FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ZFR0_SHA3_SHIFT, 4, 0),
> +	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_SVE),
> +		       FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ZFR0_BITPERM_SHIFT, 4, 0),
> +	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_SVE),
> +		       FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ZFR0_AES_SHIFT, 4, 0),
> +	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_SVE),
> +		       FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ZFR0_SVEVER_SHIFT, 4, 0),
>  	ARM64_FTR_END,
>  };
>  
> -- 
> 2.11.0
> 
> 
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