[kernel-hardening] Re: [RFC v2] implement SL*B and stack usercopy runtime checks

Vasiliy Kulikov
2011-07-18T19:24:54Z

On Mon, Jul 18, 2011 at 14:08 -0500, Matt Mackall wrote:
> On Mon, 2011-07-18 at 22:39 +0400, Vasiliy Kulikov wrote:
> > This patch implements 2 additional checks for the data copied from
> > kernelspace to userspace and vice versa (original PAX_USERCOPY from PaX
> > patch). Currently there are some very simple and cheap comparisons of
> > supplied size and the size of a copied object known at the compile time
> > in copy_* functions. This patch enhances these checks to check against
> > stack frame boundaries and against SL*B object sizes.
> >
> > More precisely, it checks:
> >
> > 1) if the data touches the stack, checks whether it fully fits in the stack
> > and whether it fully fits in a single stack frame. The latter is arch
> > dependent, currently it is implemented for x86 with CONFIG_FRAME_POINTER=y
> > only. It limits infoleaks/overwrites to a single frame and local variables
> > only, and prevents saved return instruction pointer overwriting.
> >
> > 2) if the data is from the SL*B cache, checks whether it fully fits in a
> > slab page and whether it overflows a slab object. E.g. if the memory
> > was allocated as kmalloc(64, GFP_KERNEL) and one tries to copy 150
> > bytes, the copy would fail.
>
> FYI, this should almost certainly be split into (at least) two patches:
>
> - the stack check
> - the SL*B check (probably one patch per allocator, preceded by one for
> any shared infrastructure)

Sure, also per architecture probably. But I want to get the comments
about the feature itself before the division.

Thanks,

--
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments