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

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Date:	Fri, 12 Sep 2014 21:32:20 -0700
From:	Z Lim <zlim.lnx@...il.com>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	"David S. Miller" <davem@...emloft.net>,
	Alexei Starovoitov <ast@...mgrid.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH arm64-next v2] net: bpf: arm64: address randomize and
 write protect JIT code

On Fri, Sep 12, 2014 at 10:35 AM, Daniel Borkmann <dborkman@...hat.com> 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@...hat.com>
> Cc: Zi Shen Lim <zlim.lnx@...il.com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: Alexei Starovoitov <ast@...mgrid.com>
> ---
>  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.

> +       /* 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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