linux-kernel - Re: [RESEND PATCH] x86: add phys addr validity check for /dev/mem mmap

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Message-ID: <524C6799.9060800@zytor.com>
Date:	Wed, 02 Oct 2013 11:36:09 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Frantisek Hrbata <fhrbata@...hat.com>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	oleg@...hat.com, kamaleshb@...ibm.com, hechjie@...ibm.com,
	akpm@...ux-foundation.org, dave.hansen@...el.com
Subject: Re: [RESEND PATCH] x86: add phys addr validity check for /dev/mem
 mmap

On 10/02/2013 11:31 AM, Frantisek Hrbata wrote:
> On Wed, Oct 02, 2013 at 10:46:35AM -0700, H. Peter Anvin wrote:
>> On 10/02/2013 09:05 AM, Frantisek Hrbata wrote:
>>> +
>>> +int valid_phys_addr_range(phys_addr_t addr, size_t count)
>>> +{
>>> +	return addr + count <= __pa(high_memory);
>>> +}
>>> +
>>> +int valid_mmap_phys_addr_range(unsigned long pfn, size_t count)
>>> +{
>>> +	resource_size_t addr = (pfn << PAGE_SHIFT) + count;
>>> +	return phys_addr_valid(addr);
>>> +}
>>>
>>
>> The latter has overflow problems.
> 
> Could you please specify what overflow problems do you mean?

Consider if pfn + count overflows and wraps around, or if (pfn <<
PAGE_SHIFT) pushes bits out to the left.

>> The former I realize matches the current /dev/mem, but it is still just
>> plain wrong in multiple ways.
> 
> I guess that you are talking about /dev/mem implementation generelly, because
> this patch is exactly the same as the first one. All I'm trying to do here is to
> fix this simple problem, which was reported by a customer, using IMHO the least
> invasive way. Anyway is there any description what is wrong with /dev/mem
> implementation? Maybe I can try to take a look.
> 

The bottom line is that read/write to /dev/mem should be able to access
the same memory that we can mmap().  Having two different tests is
ridiculous.

	-hpa


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