Re: Stable backport of ASLR fixes?

[Sebastian Parschauer]

On 28.07.2015 00:03, Kees Cook wrote:
> Hi Greg,
> 
> Have you had a chance to look at this? I think we need to either
> include the ASLR improvements in stable or revert
> a87938b2e246b81b4fb713edb371a9fa3c5c3c86, which breaks existing
> userspace tools.

Hi Kees,

I think it was a wrong assumption on our side as the scanmem developers.
https://github.com/scanmem/scanmem/issues/122 has been fixed by
https://github.com/scanmem/scanmem/pull/124. The stuff loaded behind the
.text region is caused by mmap() calls. Maybe the default areas for
mmap() shouldn't point to the gap between .text and .rodata of the
executable so that the regions belonging to it can be detected easier.

> On Thu, Jul 16, 2015 at 1:34 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>> On Thu, Jul 16, 2015 at 12:57 PM, Sebastian Parschauer
>> <s.parschauer@xxxxxx> wrote:
>>> I'm a professional Linux game cheater and the co-maintainer of scanmem.
>>> With scanmem we determine the load addresses for PIC and PIE binaries to
>>> be able to support static memory cheating with ASLR. At the moment
>>> ugtrain is the only universal game trainer able to determine the PIE
>>> load address as well and to re-add it to the found match offset from
>>> scanmem.
>>
>> scanmem is such a fun tool. :)
>>
>>> I'd like to complain a bit about this patch as it makes the address
>>> space layout for the executable really ugly by loading unrelated stuff
>>> between .text and .rodata.
>>>
>>> Is it really required on top of 3.13 or 3.16 where Ubuntu has put it?
>>>
>>> I've also checked v4.2-rc1. There everything is beautiful again.
>>> Thank you very much for that!
>>>
>>> References:
>>> https://github.com/scanmem/scanmem/issues/122
>>> https://github.com/ugtrain/ugtrain
>>
>> To summarize the two commits:
>>
>> This commit fixed a problem where PIE binaries could collide with
>> other memory regions, but breaks scanmem:
>> https://git.kernel.org/linus/a87938b2e246b81b4fb713edb371a9fa3c5c3c86
>> It was sent to stable (and various distros like Ubuntu picked it up),
>> since it was (correctly) seen as a bug fix (without realizing it broke
>> other programs).
>>
>> This commit reorganized PIE ASLR to split it from mmap ASLR:
>> https://git.kernel.org/linus/a87938b2e246b81b4fb713edb371a9fa3c5c3c86
>> This was part of a larger series of patches that did refactoring
>> across multiple architectures, and was not sent to stable (since it is
>> considered more of a feature than a bug fix).
>>
>> I believe it should be safe to backport the series, but not every
>> kernel team will be willing to do that on their own. As the series has
>> been living fine since 4.1, I could be convinced that it should be
>> sent to stable. It does fix an ASLR weakness, and it does fix a
>> situation where the other commit that got sent to stable breaks
>> existing userspace tools. I think both of those factors together
>> warrants sending the series to stable.
>>
>> Greg, would you be willing to take these into stable?
>>
>> fbbc400f3924ce095b466c776dc294727ec0a202
>> 82168140bc4cec7ec9bad39705518541149ff8b7
>> dd04cff1dceab18226853b555cf07914648a235f
>> 1f0569df0b0285e7ec2432d804a4921b06a61618
>> ed6322746afb74c2509e2f3a6464182793b16eb9
>> 8e89a356feb6f196824a72101861d931a97ac2d2
>> 2b68f6caeac271620cd2f9362aeaed360e317df0
>> c6f5b001e65cdac592b65a08c5d2dd179cfba568
>> d1fd836dcf00d2028c700c7e44d2c23404062c90
>> 204db6ed17743000691d930368a5abd6ea541c58
>>
>> Thanks!
>>
>> -Kees
>>
>> --
>> Kees Cook
>> Chrome OS Security
> 
> 
> 
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