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

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Date:   Wed, 24 Jan 2018 10:07:11 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Daniel Borkmann <daniel@...earbox.net>,
        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 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?
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