Subject: [PATCH 1/3] arm64: Add CONFIG_DEBUG_SET_MODULE_RONX support

From: [email-masked] (Laura Abbott)
Date: Tue, 06 May 2014 10:53:28 -0700

On 5/2/2014 8:30 AM, Will Deacon wrote:
> On Fri, May 02, 2014 at 03:07:11PM +0100, Steve Capper wrote:
>> On Thu, Apr 17, 2014 at 05:47:01PM -0700, Laura Abbott wrote:
>>> In a similar fashion to other architecture, add the infrastructure
>>> and Kconfig to enable DEBUG_SET_MODULE_RONX support. When
>>> enabled, module ranges will be marked read-only/no-execute as
>>> appropriate.
>>>
>>> Change-Id: I4251a0929b1fe6f43f84b14f0a64fed30769700e
>>> Signed-off-by: Laura Abbott <[email-masked]>
>>> ---
>>
>> [ ... ]
>>
>>> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
>>> new file mode 100644
>>> index 0000000..e48f980
>>> --- /dev/null
>>> +++ b/arch/arm64/mm/pageattr.c
>>
>> [ ... ]
>>
>>> +static int change_memory_common(unsigned long addr, int numpages,
>>> +				pgprot_t prot, bool set)
>>> +{
>>> +	unsigned long start = addr;
>>> +	unsigned long size = PAGE_SIZE*numpages;
>>> +	unsigned long end = start + size;
>>> +	int ret;
>>> +
>>> +	if (start < MODULES_VADDR || start >= MODULES_END)
>>> +		return -EINVAL;
>>> +
>>> +	if (end < MODULES_VADDR || end >= MODULES_END)
>>> +		return -EINVAL;
>>> +
>>> +	if (set)
>>> +		ret = apply_to_page_range(&init_mm, start, size,
>>> +					set_page_range, (void *)prot);
>>> +	else
>>> +		ret = apply_to_page_range(&init_mm, start, size,
>>> +					clear_page_range, (void *)prot);
>>> +
>>> +	flush_tlb_kernel_range(start, end);
>>
>> Could you please add an isb() here? (We're about to nuke the one in
>> flush_tlb_kernel_range).
> 
> Thinking about this even more (too much?), how does this work with SMP
> anyway? You need each CPU to execute an isb(), so this just a race that
> is dealt with already (probably treated as benign)?
>

Yes unless we want to IPI an isb I think this should be a mostly benign
race. I say 'mostly' only because this is a security/debug feature so
there could be a hole to take advantage of. Then again, because we map
and then set permissions later there is always a chance of a race.

I'll add the isb for v2 based on Will's patch set.

Laura

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