linux-kernel - Re: [PATCH v2 2/2] arm64: uaccess: Implement unsafe accessors

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Date:   Thu, 6 Dec 2018 18:25:52 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Julien Thierry <julien.thierry@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        peterz@...radead.org, will.deacon@....com, mingo@...hat.com,
        james.morse@....com, hpa@...or.com
Subject: Re: [PATCH v2 2/2] arm64: uaccess: Implement unsafe accessors

On Mon, Dec 03, 2018 at 01:55:18PM +0000, Julien Thierry wrote:
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index 07c3408..cabfcae 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -233,6 +233,23 @@ static inline void uaccess_enable_not_uao(void)
>  	__uaccess_enable(ARM64_ALT_PAN_NOT_UAO);
>  }
>  
> +#define unsafe_user_region_active	uaccess_region_active
> +static inline bool uaccess_region_active(void)
> +{
> +	if (system_uses_ttbr0_pan()) {
> +		u64 ttbr;
> +
> +		ttbr = read_sysreg(ttbr1_el1);
> +		return ttbr & TTBR_ASID_MASK;

Nitpick: could write this in 1-2 lines.

> +	} else if (cpus_have_const_cap(ARM64_ALT_PAN_NOT_UAO)) {
> +		return (read_sysreg(sctlr_el1) & SCTLR_EL1_SPAN) ?
> +				false :
> +				!read_sysreg_s(SYS_PSTATE_PAN);
> +	}

ARM64_ALT_PAN_NOT_UAO implies ARM64_HAS_PAN which implies SCTLR_EL1.SPAN
is 0 at run-time. Is this to cope with the case of being called prior to
cpu_enable_pan()?

-- 
Catalin