linux-kernel - Re: [PATCH 04/12] __wr_after_init: x86_64: __wr

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Message-ID: <20181220184917.GY10600@bombadil.infradead.org>
Date:   Thu, 20 Dec 2018 10:49:18 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Igor Stoppa <igor.stoppa@...il.com>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>, igor.stoppa@...wei.com,
        Nadav Amit <nadav.amit@...il.com>,
        Kees Cook <keescook@...omium.org>,
        linux-integrity@...r.kernel.org,
        kernel-hardening@...ts.openwall.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/12] __wr_after_init: x86_64: __wr_op

On Wed, Dec 19, 2018 at 11:33:30PM +0200, Igor Stoppa wrote:
> +void *__wr_op(unsigned long dst, unsigned long src, __kernel_size_t len,
> +	      enum wr_op_type op)
> +{
> +	temporary_mm_state_t prev;
> +	unsigned long offset;
> +	unsigned long wr_poking_addr;
> +
> +	/* Confirm that the writable mapping exists. */
> +	if (WARN_ONCE(!wr_ready, "No writable mapping available"))
> +		return (void *)dst;
> +
> +	if (WARN_ONCE(op >= WR_OPS_NUMBER, "Invalid WR operation.") ||
> +	    WARN_ONCE(!is_wr_after_init(dst, len), "Invalid WR range."))
> +		return (void *)dst;
> +
> +	offset = dst - (unsigned long)&__start_wr_after_init;
> +	wr_poking_addr = wr_poking_base + offset;
> +	local_irq_disable();
> +	prev = use_temporary_mm(wr_poking_mm);
> +
> +	if (op == WR_MEMCPY)
> +		copy_to_user((void __user *)wr_poking_addr, (void *)src, len);
> +	else if (op == WR_MEMSET)
> +		memset_user((void __user *)wr_poking_addr, (u8)src, len);
> +
> +	unuse_temporary_mm(prev);
> +	local_irq_enable();
> +	return (void *)dst;
> +}

I think you're causing yourself more headaches by implementing this "op"
function.  Here's some generic code:

void *wr_memcpy(void *dst, void *src, unsigned int len)
{
	wr_state_t wr_state;
	void *wr_poking_addr = __wr_addr(dst);

	local_irq_disable();
	wr_enable(&wr_state);
	__wr_memcpy(wr_poking_addr, src, len);
	wr_disable(&wr_state);
	local_irq_enable();

	return dst;
}

Now, x86 can define appropriate macros and functions to use the temporary_mm
functionality, and other architectures can do what makes sense to them.