linux-kernel - Re: [PATCH v2 4/6] x86/alternatives: initializing temporary mm for patching

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Date:   Thu, 6 Sep 2018 11:01:42 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nadav Amit <namit@...are.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH v2 4/6] x86/alternatives: initializing temporary mm for
 patching

On Sun, Sep 02, 2018 at 10:32:22AM -0700, Nadav Amit wrote:
> +void __init poking_init(void)
> +{
> +	unsigned long poking_addr;
> +
> +	poking_mm = copy_init_mm();
> +	if (!poking_mm) {
> +		pr_err("x86/mm: error setting a separate poking address space");
> +		return;
> +	}
> +
> +	/*
> +	 * Randomize the poking address, but make sure that the following page
> +	 * will be mapped at the same PMD. We need 2 pages, so find space for 3,
> +	 * and adjust the address if the PMD ends after the first one.
> +	 */
> +	poking_addr = TASK_UNMAPPED_BASE +
> +		(kaslr_get_random_long("Poking") & PAGE_MASK) %
> +		(TASK_SIZE - TASK_UNMAPPED_BASE - 3 * PAGE_SIZE);
> +
> +	if (((poking_addr + PAGE_SIZE) & ~PMD_MASK) == 0)
> +		poking_addr += PAGE_SIZE;
> +}

This fails to compile for me.. I don't have kaslr_get_random_long().