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

[David Brown]

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.

David