linux-kernel - Re: [PATCH] x86 - Enhance DEBUG_RODATA support

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Message-ID: <47D014E1.30964.22A9390F@pageexec.freemail.hu>
Date:	Thu, 06 Mar 2008 15:59:29 +0200
From:	pageexec@...email.hu
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Ingo Molnar <mingo@...e.hu>
CC:	Srinivasa DS <srinivasa@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, ananth@...ibm.com,
	Jim Keniston <jkenisto@...ibm.com>, srikar@...ux.vnet.ibm.com,
	SystemTAP <systemtap@...rces.redhat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH] x86 - Enhance DEBUG_RODATA support - alternatives

On 6 Mar 2008 at 15:01, Ingo Molnar wrote:

> +/**
> + * text_poke - Update instructions on a live kernel
> + * @addr: address to modify
> + * @opcode: source of the copy
> + * @len: length to copy
> + *
> + * Only atomic text poke/set should be allowed when not doing early patching.
> + * It means the size must be writable atomically and the address must be aligned
> + * in a way that permits an atomic write. It also makes sure we fit on a single
> + * page.
> + */
> +void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
> +{
> +	unsigned long flags;
> +	char *vaddr;
> +	int nr_pages = 2;
> +
> +	BUG_ON(len > sizeof(long));
> +	BUG_ON((((long)addr + len - 1) & ~(sizeof(long) - 1))
> +		- ((long)addr & ~(sizeof(long) - 1)));
> +	{
> +		struct page *pages[2] = { virt_to_page(addr),
> +			virt_to_page(addr + PAGE_SIZE) };
> +		if (!pages[1])
> +			nr_pages = 1;
> +		vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
> +		WARN_ON(!vaddr);
> +		local_irq_save(flags);
> +		memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
> +		local_irq_restore(flags);

you probably want a BUG_ON instead (or some graceful recovery) else
the NULL deref will trigger with IRQs off...

> +		vunmap(vaddr);
> +	}
>  	sync_core();
>  	/* Could also do a CLFLUSH here to speed up CPU recovery; but
>  	   that causes hangs on some VIA CPUs. */
> +	return addr;
>  }


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