From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: [PATCH v3 bpf] bpf: introduce BPF_JIT_ALWAYS_ON config Date: Wed, 24 Jan 2018 10:07:11 +0000 Message-ID: <1516788431.13558.109.camel@infradead.org> References: <20180109180429.1115005-1-ast@kernel.org> <606bf504-a39f-288d-11cd-56888ecbc165@iogearbox.net> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-T/cCaYMCILaj8CO2YzKv" Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, "stable@vger.kernel.org" , "dave.hansen@linux.intel.com" To: Daniel Borkmann , Alexei Starovoitov , davem@davemloft.net Return-path: In-Reply-To: <606bf504-a39f-288d-11cd-56888ecbc165@iogearbox.net> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org --=-T/cCaYMCILaj8CO2YzKv Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2018-01-09 at 22:39 +0100, Daniel Borkmann wrote: > On 01/09/2018 07:04 PM, Alexei Starovoitov wrote: > >=20 > > The BPF interpreter has been used as part of the spectre 2 attack CVE-2= 017-5715. > >=20 > > 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 annoyin= g. > > 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 in= side > > a VM, the presence of the code in the host kernel's text section is suf= ficient > > to make it usable for the attack, just like with ordinary ROP gadgets." > >=20 > > To make attacker job harder introduce BPF_JIT_ALWAYS_ON config > > option that removes interpreter from the kernel in favor of JIT-only mo= de. > > So far eBPF JIT is supported by: > > x64, arm64, arm32, sparc64, s390, powerpc64, mips64 > >=20 > > The start of JITed program is randomized and code page is marked as rea= d-only. > > In addition "constant blinding" can be turned on with net.core.bpf_jit_= harden > >=20 > > v2->v3: > > - move __bpf_prog_ret0 under ifdef (Daniel) > >=20 > > 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. > > =C2=A0 It will be sent when the trees are merged back to net-next > >=20 > > Considered doing: > > =C2=A0 int bpf_jit_enable __read_mostly =3D 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. > >=20 > > Signed-off-by: Alexei Starovoitov > > Applied to bpf tree, thanks Alexei! 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