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

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Message-ID: <82ee2a7c-1061-f954-4ff1-3dfb94ec3419@arm.com>
Date:   Mon, 14 Oct 2019 16:30:01 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Julien Grall <julien.grall@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     catalin.marinas@....com, will@...nel.org, Dave.Martin@....com
Subject: Re: [PATCH] arm64: cpufeature: Don't expose ZFR0 to userspace when
 SVE is not enabled

Hi Julien,

Some minor nits in the description.

On 14/10/2019 11:21, 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.

s/used/use ?

> Therefore, we only need to hidden them from the userspace.

s/hidden/hide ?

With the above:

Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>

> 
> Signed-off-by: Julien Grall <julien.grall@....com>
> Fixes: 06a916feca2b ('arm64: Expose SVE2 features for userspace')
> ---
>   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,
>   };
>   
>