linux-kernel - Re: [PATCH v4 2/8] riscv/kprobe: Allocate detour buffer from module area

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Message-ID: <20221116202521.6c528955@gandalf.local.home>
Date:   Wed, 16 Nov 2022 20:25:21 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Chen Guokai <chenguokai17@...ls.ucas.ac.cn>
Cc:     paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, mingo@...hat.com, sfr@...b.auug.org.au,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        liaochang1@...wei.com, Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v4 2/8] riscv/kprobe: Allocate detour buffer from module
 area

On Sun,  6 Nov 2022 18:03:10 +0800
Chen Guokai <chenguokai17@...ls.ucas.ac.cn> wrote:

> @@ -84,6 +85,30 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>  }
>  
>  #ifdef CONFIG_MMU
> +#if defined(CONFIG_OPTPROBES) && defined(CONFIG_64BIT)
> +void *alloc_optinsn_page(void)
> +{
> +	void *page;
> +
> +	page = __vmalloc_node_range(PAGE_SIZE, 1, MODULES_VADDR,
> +				    MODULES_END, GFP_KERNEL,
> +				    PAGE_KERNEL, 0, NUMA_NO_NODE,
> +				    __builtin_return_address(0));
> +	if (!page)
> +		return NULL;
> +
> +	set_vm_flush_reset_perms(page);
> +	/*
> +	 * First make the page read-only, and only then make it executable to
> +	 * prevent it from being W+X in between.
> +	 */
> +	set_memory_ro((unsigned long)page, 1);
> +	set_memory_x((unsigned long)page, 1);

FYI, the above combination is going to be going away:

  https://lore.kernel.org/all/Y10OyLCLAAS6rsZv@hirez.programming.kicks-ass.net/

-- Steve


> +
> +	return page;
> +}
> +#endif
> +