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

quoted text
> +/**
> + * 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...

quoted text
> +		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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