Re: [PATCH arm64-next v2] net: bpf: arm64: address randomize and write protect JIT code

[Will Deacon]

On Mon, Sep 15, 2014 at 02:52:40PM +0100, Daniel Borkmann wrote:
> On 09/13/2014 06:32 AM, Z Lim wrote:
> > On Fri, Sep 12, 2014 at 10:35 AM, Daniel Borkmann <dborkman@xxxxxxxxxx> wrote:
> >> This is the ARM64 variant for 314beb9bcab ("x86: bpf_jit_comp: secure bpf
> >> jit against spraying attacks").
> >>
> >> Thanks to commit 11d91a770f1f ("arm64: Add CONFIG_DEBUG_SET_MODULE_RONX
> >> support") which added necessary infrastructure, we can now implement
> >> RO marking of eBPF generated JIT image pages and randomize start offset
> >> for the JIT code, so that it does not reside directly on a page boundary
> >> anymore. Likewise, the holes are filled with illegal instructions.
> >>
> >> This is basically the ARM64 variant of what we already have in ARM via
> >> commit 55309dd3d4cd ("net: bpf: arm: address randomize and write protect
> >> JIT code"). Moreover, this commit also presents a merge resolution due to
> >> conflicts with commit 60a3b2253c41 ("net: bpf: make eBPF interpreter images
> >> read-only") as we don't use kfree() in bpf_jit_free() anymore to release
> >> the locked bpf_prog structure, but instead bpf_prog_unlock_free() through
> >> a different allocator.
> >>
> >> JIT tested on aarch64 with BPF test suite.
> >>
> >> Reference: http://mainisusuallyafunction.blogspot.com/2012/11/attacking-hardened-linux-systems-with.html
> >> Signed-off-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
> >> Cc: Zi Shen Lim <zlim.lnx@xxxxxxxxx>
> >> Cc: Will Deacon <will.deacon@xxxxxxx>
> >> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> >> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> >> Cc: Alexei Starovoitov <ast@xxxxxxxxxxxx>
> >> ---
> >>   v1 -> v2:
> >>    - Use brk insn as suggested by Catalin, thanks a lot for
> >>      your feedback! Rest unchanged.
> >>   Note:
> >>    - This patch depends on net-next being merged to mainline due
> >>      to the mentioned merge conflict.
> >>
> >>   arch/arm64/net/bpf_jit_comp.c | 38 +++++++++++++++++++++++++++++---------
> >>   1 file changed, 29 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
> >> index 7ae3354..4b71779 100644
> >> --- a/arch/arm64/net/bpf_jit_comp.c
> >> +++ b/arch/arm64/net/bpf_jit_comp.c
> >> @@ -19,7 +19,6 @@
> >>   #define pr_fmt(fmt) "bpf_jit: " fmt
> >>
> >>   #include <linux/filter.h>
> >> -#include <linux/moduleloader.h>
> >>   #include <linux/printk.h>
> >>   #include <linux/skbuff.h>
> >>   #include <linux/slab.h>
> >> @@ -119,6 +118,15 @@ static inline int bpf2a64_offset(int bpf_to, int bpf_from,
> >>          return to - from;
> >>   }
> >>
> >> +static void jit_fill_hole(void *area, unsigned int size)
> >> +{
> >> +       /* We use brk #0x100 to trigger a fault. */
> >> +       u32 *ptr, fill_ins = 0xd4202000;
> >
> > Missed this on first round of review, I think we also need
> > cpu_to_le32(...) here.
> 
> Just wondering ... so that would also hold true in case I build/run my
> kernel in big-endian (CPU_BIG_ENDIAN)?

Yes, the instruction stream is always little endian so the conversion is
required.

Will

> >> +       /* We are guaranteed to have aligned memory. */
> >> +       for (ptr = area; size >= sizeof(u32); size -= sizeof(u32))
> >> +               *ptr++ = fill_ins;
> >> +}
> >> +
> > [...]
> >
> > Thanks Daniel.
> 
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