Re: [PATCH arm64-next v4] net: bpf: arm64: address randomize and write protect JIT code

[Will Deacon]

On Tue, Sep 16, 2014 at 08:48:50AM +0100, Daniel Borkmann 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: here
> we use BRK #0x100 (opcode 0xd4202000) to trigger a fault in the kernel
> (unallocated BRKs would trigger a fault through do_debug_exception). This
> seems more reliable as we don't have a guaranteed undefined instruction
> space on ARM64.
> 
> 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>
> ---
>  v3->v4:
>   - Inclusion into debug-monitors.h as suggested by Will
>  v2->v3:
>   - Use cpu_to_le32() as suggested by Zi/Will
>  v1->v2:
>   - Use brk insn as suggested by Catalin
>  Note:
>   - This patch depends on net-next being merged to mainline due
>     to the mentioned merge conflict.
> 
>  arch/arm64/include/asm/debug-monitors.h |  8 +++++++
>  arch/arm64/net/bpf_jit_comp.c           | 39 +++++++++++++++++++++++++--------
>  2 files changed, 38 insertions(+), 9 deletions(-)

Thanks, Daniel, this looks great:

  Acked-by: Will Deacon <will.deacon@xxxxxxx>

We can merge this at -rc1.

Will
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