Messages in this thread | | | Date | Wed, 17 Feb 2016 16:43:06 -0700 | From | David Brown <> | Subject | Re: [PATCH] ARM: vdso: Mark vDSO code as read-only |
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On Wed, Feb 17, 2016 at 03:00:52PM -0800, Kees Cook wrote: >On Tue, Feb 16, 2016 at 9:20 PM, David Brown <david.brown@linaro.org> 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@linaro.org> >>> 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...)
However, this distinction between .rodata and .data..ro_after_init is kind of fuzzy, anyway, since they both get made actually read-only at the same time (post init). The patch actually does work fine with the vDSO page in .rodata, since the patching happens during init.
Is there a possible future consideration to perhaps make .rodata read only much earlier?
David
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