netdev - Re: [PATCH v3 bpf] bpf: introduce BPF_JIT_ALWAYS

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Date:   Wed, 24 Jan 2018 11:10:50 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     David Woodhouse <dwmw2@...radead.org>,
        Alexei Starovoitov <ast@...nel.org>, davem@...emloft.net
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v3 bpf] bpf: introduce BPF_JIT_ALWAYS_ON config

On 01/24/2018 11:07 AM, David Woodhouse wrote:
> On Tue, 2018-01-09 at 22:39 +0100, Daniel Borkmann wrote:
>> On 01/09/2018 07:04 PM, Alexei Starovoitov wrote:
>>>
>>> The BPF interpreter has been used as part of the spectre 2 attack CVE-2017-5715.
>>>
>>> A quote from goolge project zero blog:
>>> "At this point, it would normally be necessary to locate gadgets in
>>> the host kernel code that can be used to actually leak data by reading
>>> from an attacker-controlled location, shifting and masking the result
>>> appropriately and then using the result of that as offset to an
>>> attacker-controlled address for a load. But piecing gadgets together
>>> and figuring out which ones work in a speculation context seems annoying.
>>> So instead, we decided to use the eBPF interpreter, which is built into
>>> the host kernel - while there is no legitimate way to invoke it from inside
>>> a VM, the presence of the code in the host kernel's text section is sufficient
>>> to make it usable for the attack, just like with ordinary ROP gadgets."
>>>
>>> To make attacker job harder introduce BPF_JIT_ALWAYS_ON config
>>> option that removes interpreter from the kernel in favor of JIT-only mode.
>>> So far eBPF JIT is supported by:
>>> x64, arm64, arm32, sparc64, s390, powerpc64, mips64
>>>
>>> The start of JITed program is randomized and code page is marked as read-only.
>>> In addition "constant blinding" can be turned on with net.core.bpf_jit_harden
>>>
>>> v2->v3:
>>> - move __bpf_prog_ret0 under ifdef (Daniel)
>>>
>>> v1->v2:
>>> - fix init order, test_bpf and cBPF (Daniel's feedback)
>>> - fix offloaded bpf (Jakub's feedback)
>>> - add 'return 0' dummy in case something can invoke prog->bpf_func
>>> - retarget bpf tree. For bpf-next the patch would need one extra hunk.
>>>   It will be sent when the trees are merged back to net-next
>>>
>>> Considered doing:
>>>   int bpf_jit_enable __read_mostly = BPF_EBPF_JIT_DEFAULT;
>>> but it seems better to land the patch as-is and in bpf-next remove
>>> bpf_jit_enable global variable from all JITs, consolidate in one place
>>> and remove this jit_init() function.
>>>
>>> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
>>
>> Applied to bpf tree, thanks Alexei!
> 
> For stable too?

Yes, this will go into stable as well; batch of backports will come Thurs/Fri.