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

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Date:	Tue, 16 Sep 2014 09:29:30 -0700
From:	Z Lim <zlim.lnx@...il.com>
To:	Will Deacon <will.deacon@....com>
Cc:	Daniel Borkmann <dborkman@...hat.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Alexei Starovoitov <ast@...mgrid.com>
Subject: Re: [PATCH arm64-next v4] net: bpf: arm64: address randomize and
 write protect JIT code

On Tue, Sep 16, 2014 at 9:25 AM, Will Deacon <will.deacon@....com> wrote:
> 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@...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>
>> ---
>>  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@....com>
>

Reviewed-by: Zi Shen Lim <zlim.lnx@...il.com>

> We can merge this at -rc1.
>
> Will
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