Re: [PATCH] ARM: vdso: Mark vDSO code as read-only

[Kees Cook]

On Tue, Feb 16, 2016 at 9:20 PM, David Brown <david.brown@xxxxxxxxxx> wrote:
> On Tue, Feb 16, 2016 at 01:52:33PM -0800, Kees Cook wrote:
>>
>> On Tue, Feb 16, 2016 at 1:36 PM, David Brown <david.brown@xxxxxxxxxx>
>> wrote:
>>>
>>> Although the arm vDSO is cleanly separated by code/data with the code
>>> being read-only in userspace mappings, the code page is still writable
>>> from the kernel.  There have been exploits (such as
>>> http://itszn.com/blog/?p=21) that take advantage of this on x86 to go
>>> from a bad kernel write to full root.
>>>
>>> Prevent this specific exploit on arm by putting the vDSO code page in
>>> post-init read-only memory as well.
>>
>>
>> Is the vdso dynamically built at init time like on x86, or can this
>> just use .rodata directly?
>
>
> On ARM, it is patched during init.  Arm64's is just plain read-only.

Okay, great. I've added this to my postinit-readonly series (which I
just refreshed and sent out again...)

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security