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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Christophe Leroy <christophe.leroy@c-s.fr>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>, ruscur@russell.cc
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2 10/10] powerpc/32s: Implement Kernel Userspace Access Protection
In-Reply-To: <a2847248a92cb1641b1740fa121c5a30593ae662.1552292207.git.christophe.leroy@c-s.fr>
References: <cover.1552292207.git.christophe.leroy@c-s.fr> <a2847248a92cb1641b1740fa121c5a30593ae662.1552292207.git.christophe.leroy@c-s.fr>
Date:   Thu, 18 Apr 2019 16:55:30 +1000
Message-ID: <87ftqfu7j1.fsf@concordia.ellerman.id.au>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Christophe Leroy <christophe.leroy@c-s.fr> writes:
> diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h
> index 5f97c742ca71..b3560b2de435 100644
> --- a/arch/powerpc/include/asm/book3s/32/kup.h
> +++ b/arch/powerpc/include/asm/book3s/32/kup.h
> @@ -37,6 +37,113 @@
...
> +
> +static inline void allow_user_access(void __user *to, const void __user *from, u32 size)
> +{
> +	u32 addr = (__force u32)to;
> +	u32 end = min(addr + size, TASK_SIZE);
> +
> +	if (!addr || addr >= TASK_SIZE || !size)
> +		return;
> +
> +	current->thread.kuap = (addr & 0xf0000000) | ((((end - 1) >> 28) + 1) & 0xf);
> +	kuap_update_sr(mfsrin(addr) & ~SR_KS, addr, end);	/* Clear Ks */
> +}

When rebasing on my v6 I changed the above to:

static inline void allow_user_access(void __user *to, const void __user *from, u32 size)
{
	u32 addr, end;

	if (__builtin_constant_p(to) && to == NULL)
		return;

	addr = (__force u32)to;

	if (!addr || addr >= TASK_SIZE || !size)
		return;

	end = min(addr + size, TASK_SIZE);
	current->thread.kuap = (addr & 0xf0000000) | ((((end - 1) >> 28) + 1) & 0xf);
	kuap_update_sr(mfsrin(addr) & ~SR_KS, addr, end);	/* Clear Ks */
}

Which I think achieves the same result. It does boot :)

> +
> +static inline void prevent_user_access(void __user *to, const void __user *from, u32 size)
> +{
> +	u32 addr = (__force u32)to;
> +	u32 end = min(addr + size, TASK_SIZE);
> +
> +	if (!addr || addr >= TASK_SIZE || !size)
> +		return;
> +
> +	current->thread.kuap = 0;
> +	kuap_update_sr(mfsrin(addr) | SR_KS, addr, end);	/* set Ks */
> +}
> +
> +static inline void allow_read_from_user(const void __user *from, unsigned long size)
> +{
> +}

And I dropped that.

cheers