• Alexei Starovoitov's avatar
    bpf: introduce BPF_JIT_ALWAYS_ON config · 6fde36d5
    Alexei Starovoitov authored
    [ upstream commit 290af866 ]
    
    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: default avatarAlexei Starovoitov <ast@kernel.org>
    Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    6fde36d5