linux-kernel - Re: [PATCH v4 07/36] arm64/gcs: Provide copy_to_user

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Date:   Fri, 11 Aug 2023 17:36:05 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Will Deacon <will@...nel.org>, Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Arnd Bergmann <arnd@...db.de>, Oleg Nesterov <oleg@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Shuah Khan <shuah@...nel.org>,
        "Rick P. Edgecombe" <rick.p.edgecombe@...el.com>,
        Deepak Gupta <debug@...osinc.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>,
        "H.J. Lu" <hjl.tools@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        kvmarm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v4 07/36] arm64/gcs: Provide copy_to_user_gcs()

On Mon, Aug 07, 2023 at 11:00:12PM +0100, Mark Brown wrote:
> +static inline int copy_to_user_gcs(unsigned long __user *addr,
> +				   unsigned long *val,
> +				   int count)
> +{
> +	int ret = -EFAULT;
> +	int i;
> +
> +	if (access_ok((char __user *)addr, count * sizeof(u64))) {
> +		uaccess_ttbr0_enable();
> +		for (i = 0; i < count; i++) {
> +			ret = gcssttr(addr++, *val++);
> +			if (ret != 0)
> +				break;
> +		}
> +		uaccess_ttbr0_disable();
> +	}
> +
> +	return ret;
> +}

I think it makes more sense to have a put_user_gcs() of a single
element. I've only seen it used with 2 elements in the signal code but
we could as well do two put_user_gcs() calls (as we do for other stuff
that we push to the signal frame).

-- 
Catalin