Re: [RFC PATCH] kernel: Enable XDP

[Michael Tremer <michael.tremer@ipfire.org>]

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Hello,

> On 22 Apr 2024, at 16:24, Vincent Li <vincent.mc.li(a)gmail.com> wrote:
> 
> On Sun, Apr 21, 2024 at 2:04 PM Peter Müller <peter.mueller(a)ipfire.org> wrote:
>> 
>> Hello Michael,
>> 
>> thank you for working on this in particular and the SYNPROXY patchset.
>> 
>> If my understanding of the situation is correct, the changes this patch
>> proposes would only be necessary for Vincent Li's DDoS mitigation that
>> leverages XDP, which remains a custom setup IPFire otherwise does not
>> support (in terms of having it documented, supported by the web interface,
>> etc.).

XDP is not configurable in the kernel. It is always compiled in as it depends on the driver whether it is being implemented.

What Vincent is asking for is to enable the BPF syscall.

>> Frankly, I still think that the misuse potential of having XDP enabled
>> outweighs the benefits of doing so, and I'd rather not see this attack
>> surface being opened by default on IPFire systems, "just" to permit one
>> single custom setup of which the exact nature and benefit still largely
>> remains unclear to me. Personally, I'd much rather see the SYNPROXY patchset
>> you submitted land in IPFire, be properly supported, and enabled by default.
> 
> What attack interface XDP exposed? I guess you mean the eBPF feature
> enabled in general
> could expose attack interfaces. the kernel config I suggested as I
> researched, only enable
> XDP/TC network functionality, no tracing functionality ( which
> requires admin privilege even enabled).

What Peter means is that the larger the codebase the larger the amount of exploitable bugs. IPFire generally tries to minimise the attack surface by disabling features that are not being used.

XDP cannot be disabled. There is not even a switch for it. So, that will always be there.

BPF cannot be disabled either as it is being enabled by default if the kernel is being compiled with network support:

  https://git.ipfire.org/?p=thirdparty/kernel/stable.git;a=blob;f=net/Kconfig;hb=ba151416051a45ffca565f708584b9cd5c971481#l10

> Enabling this allows IPFire users to customize their packet filter
> strategy, it opens up many
> possibilities, for example there is bpfilter project to improve
> iptables/nftables https://github.com/facebook/bpfilter.
> It allows innovation and progress :)

Not everything that is new is automatically innovation.

> 
>> No offense.
>> 
>> Thanks, and best regards,
>> Peter Müller
>> 
>> 
>>>  https://lists.ipfire.org/hyperkitty/list/development(a)lists.ipfire.org/thread/S4GPL3OBFZ6LMA52JNLHIOPMNA5C3V6R/
>>> 
>>> Signed-off-by: Michael Tremer <michael.tremer(a)ipfire.org>
>>> ---
>>> config/kernel/kernel.config.aarch64-ipfire | 11 ++++++++++-
>>> config/kernel/kernel.config.riscv64-ipfire | 13 ++++++++++++-
>>> config/kernel/kernel.config.x86_64-ipfire  | 11 ++++++++++-
>>> 3 files changed, 32 insertions(+), 3 deletions(-)
>>> 
>>> diff --git a/config/kernel/kernel.config.aarch64-ipfire b/config/kernel/kernel.config.aarch64-ipfire
>>> index b85d7add9..3d8282ac6 100644
>>> --- a/config/kernel/kernel.config.aarch64-ipfire
>>> +++ b/config/kernel/kernel.config.aarch64-ipfire
>>> @@ -93,9 +93,12 @@ CONFIG_ARCH_WANT_DEFAULT_BPF_JIT=y
>>> #
>>> # BPF subsystem
>>> #
>>> -# CONFIG_BPF_SYSCALL is not set
>>> +CONFIG_BPF_SYSCALL=y
>>> CONFIG_BPF_JIT=y
>>> +CONFIG_BPF_JIT_ALWAYS_ON=y
>>> CONFIG_BPF_JIT_DEFAULT_ON=y
>>> +CONFIG_BPF_UNPRIV_DEFAULT_OFF=y
>>> +# CONFIG_BPF_PRELOAD is not set
>>> # end of BPF subsystem
>>> 
>>> CONFIG_PREEMPT_BUILD=y
>>> @@ -136,6 +139,7 @@ CONFIG_TREE_SRCU=y
>>> CONFIG_TASKS_RCU_GENERIC=y
>>> CONFIG_TASKS_RCU=y
>>> CONFIG_TASKS_RUDE_RCU=y
>>> +CONFIG_TASKS_TRACE_RCU=y
>>> CONFIG_RCU_STALL_COMMON=y
>>> CONFIG_RCU_NEED_SEGCBLIST=y
>>> # end of RCU Subsystem
>>> @@ -179,6 +183,7 @@ CONFIG_PROC_PID_CPUSET=y
>>> CONFIG_CGROUP_DEVICE=y
>>> CONFIG_CGROUP_CPUACCT=y
>>> CONFIG_CGROUP_PERF=y
>>> +# CONFIG_CGROUP_BPF is not set
>>> # CONFIG_CGROUP_MISC is not set
>>> # CONFIG_CGROUP_DEBUG is not set
>>> CONFIG_SOCK_CGROUP_DATA=y
>>> @@ -1036,6 +1041,8 @@ CONFIG_XFRM_ESP=m
>>> CONFIG_XFRM_IPCOMP=m
>>> CONFIG_NET_KEY=m
>>> CONFIG_NET_KEY_MIGRATE=y
>>> +CONFIG_XDP_SOCKETS=y
>>> +CONFIG_XDP_SOCKETS_DIAG=m
>>> CONFIG_NET_HANDSHAKE=y
>>> CONFIG_INET=y
>>> CONFIG_IP_MULTICAST=y
>>> @@ -1144,6 +1151,7 @@ CONFIG_NETFILTER_SKIP_EGRESS=y
>>> CONFIG_NETFILTER_NETLINK=m
>>> CONFIG_NETFILTER_FAMILY_BRIDGE=y
>>> CONFIG_NETFILTER_FAMILY_ARP=y
>>> +CONFIG_NETFILTER_BPF_LINK=y
>>> # CONFIG_NETFILTER_NETLINK_HOOK is not set
>>> CONFIG_NETFILTER_NETLINK_ACCT=m
>>> CONFIG_NETFILTER_NETLINK_QUEUE=m
>>> @@ -6466,6 +6474,7 @@ CONFIG_HID_ZYDACRON=m
>>> #
>>> # HID-BPF support
>>> #
>>> +# CONFIG_HID_BPF is not set
>>> # end of HID-BPF support
>>> 
>>> #
>>> diff --git a/config/kernel/kernel.config.riscv64-ipfire b/config/kernel/kernel.config.riscv64-ipfire
>>> index 2bd39e7de..fd2172a25 100644
>>> --- a/config/kernel/kernel.config.riscv64-ipfire
>>> +++ b/config/kernel/kernel.config.riscv64-ipfire
>>> @@ -103,8 +103,13 @@ CONFIG_HAVE_EBPF_JIT=y
>>> #
>>> # BPF subsystem
>>> #
>>> -# CONFIG_BPF_SYSCALL is not set
>>> +CONFIG_BPF_SYSCALL=y
>>> CONFIG_BPF_JIT=y
>>> +CONFIG_BPF_JIT_ALWAYS_ON=y
>>> +CONFIG_BPF_JIT_DEFAULT_ON=y
>>> +CONFIG_BPF_UNPRIV_DEFAULT_OFF=y
>>> +# CONFIG_BPF_PRELOAD is not set
>>> +# CONFIG_BPF_LSM is not set
>>> # end of BPF subsystem
>>> 
>>> CONFIG_PREEMPT_VOLUNTARY_BUILD=y
>>> @@ -139,6 +144,7 @@ CONFIG_TREE_RCU=y
>>> CONFIG_TREE_SRCU=y
>>> CONFIG_TASKS_RCU_GENERIC=y
>>> CONFIG_TASKS_RUDE_RCU=y
>>> +CONFIG_TASKS_TRACE_RCU=y
>>> CONFIG_RCU_STALL_COMMON=y
>>> CONFIG_RCU_NEED_SEGCBLIST=y
>>> # end of RCU Subsystem
>>> @@ -180,6 +186,7 @@ CONFIG_PROC_PID_CPUSET=y
>>> CONFIG_CGROUP_DEVICE=y
>>> CONFIG_CGROUP_CPUACCT=y
>>> CONFIG_CGROUP_PERF=y
>>> +# CONFIG_CGROUP_BPF is not set
>>> # CONFIG_CGROUP_MISC is not set
>>> # CONFIG_CGROUP_DEBUG is not set
>>> CONFIG_SOCK_CGROUP_DATA=y
>>> @@ -826,6 +833,8 @@ CONFIG_XFRM_ESP=m
>>> CONFIG_XFRM_IPCOMP=m
>>> CONFIG_NET_KEY=m
>>> CONFIG_NET_KEY_MIGRATE=y
>>> +CONFIG_XDP_SOCKETS=y
>>> +CONFIG_XDP_SOCKETS_DIAG=m
>>> CONFIG_NET_HANDSHAKE=y
>>> CONFIG_INET=y
>>> CONFIG_IP_MULTICAST=y
>>> @@ -934,6 +943,7 @@ CONFIG_NETFILTER_SKIP_EGRESS=y
>>> CONFIG_NETFILTER_NETLINK=y
>>> CONFIG_NETFILTER_FAMILY_BRIDGE=y
>>> CONFIG_NETFILTER_FAMILY_ARP=y
>>> +CONFIG_NETFILTER_BPF_LINK=y
>>> # CONFIG_NETFILTER_NETLINK_HOOK is not set
>>> CONFIG_NETFILTER_NETLINK_ACCT=m
>>> CONFIG_NETFILTER_NETLINK_QUEUE=m
>>> @@ -7383,6 +7393,7 @@ CONFIG_BRANCH_PROFILE_NONE=y
>>> # CONFIG_PROFILE_ANNOTATED_BRANCHES is not set
>>> # CONFIG_BLK_DEV_IO_TRACE is not set
>>> CONFIG_UPROBE_EVENTS=y
>>> +CONFIG_BPF_EVENTS=y
>>> CONFIG_DYNAMIC_EVENTS=y
>>> CONFIG_PROBE_EVENTS=y
>>> CONFIG_FTRACE_MCOUNT_RECORD=y
>>> diff --git a/config/kernel/kernel.config.x86_64-ipfire b/config/kernel/kernel.config.x86_64-ipfire
>>> index 8ce66cb4f..ec3bca2e7 100644
>>> --- a/config/kernel/kernel.config.x86_64-ipfire
>>> +++ b/config/kernel/kernel.config.x86_64-ipfire
>>> @@ -113,9 +113,12 @@ CONFIG_ARCH_WANT_DEFAULT_BPF_JIT=y
>>> #
>>> # BPF subsystem
>>> #
>>> -# CONFIG_BPF_SYSCALL is not set
>>> +CONFIG_BPF_SYSCALL=y
>>> CONFIG_BPF_JIT=y
>>> +CONFIG_BPF_JIT_ALWAYS_ON=y
>>> CONFIG_BPF_JIT_DEFAULT_ON=y
>>> +CONFIG_BPF_UNPRIV_DEFAULT_OFF=y
>>> +# CONFIG_BPF_PRELOAD is not set
>>> # end of BPF subsystem
>>> 
>>> CONFIG_PREEMPT_BUILD=y
>>> @@ -156,6 +159,7 @@ CONFIG_TREE_SRCU=y
>>> CONFIG_TASKS_RCU_GENERIC=y
>>> CONFIG_TASKS_RCU=y
>>> CONFIG_TASKS_RUDE_RCU=y
>>> +CONFIG_TASKS_TRACE_RCU=y
>>> CONFIG_RCU_STALL_COMMON=y
>>> CONFIG_RCU_NEED_SEGCBLIST=y
>>> # end of RCU Subsystem
>>> @@ -199,6 +203,7 @@ CONFIG_PROC_PID_CPUSET=y
>>> CONFIG_CGROUP_DEVICE=y
>>> CONFIG_CGROUP_CPUACCT=y
>>> CONFIG_CGROUP_PERF=y
>>> +# CONFIG_CGROUP_BPF is not set
>>> # CONFIG_CGROUP_MISC is not set
>>> # CONFIG_CGROUP_DEBUG is not set
>>> CONFIG_SOCK_CGROUP_DATA=y
>>> @@ -1099,6 +1104,8 @@ CONFIG_XFRM_ESP=m
>>> CONFIG_XFRM_IPCOMP=m
>>> CONFIG_NET_KEY=m
>>> CONFIG_NET_KEY_MIGRATE=y
>>> +CONFIG_XDP_SOCKETS=y
>>> +CONFIG_XDP_SOCKETS_DIAG=m
>>> CONFIG_NET_HANDSHAKE=y
>>> CONFIG_INET=y
>>> CONFIG_IP_MULTICAST=y
>>> @@ -1207,6 +1214,7 @@ CONFIG_NETFILTER_SKIP_EGRESS=y
>>> CONFIG_NETFILTER_NETLINK=y
>>> CONFIG_NETFILTER_FAMILY_BRIDGE=y
>>> CONFIG_NETFILTER_FAMILY_ARP=y
>>> +CONFIG_NETFILTER_BPF_LINK=y
>>> # CONFIG_NETFILTER_NETLINK_HOOK is not set
>>> CONFIG_NETFILTER_NETLINK_ACCT=m
>>> CONFIG_NETFILTER_NETLINK_QUEUE=m
>>> @@ -5861,6 +5869,7 @@ CONFIG_HID_SENSOR_HUB=m
>>> #
>>> # HID-BPF support
>>> #
>>> +# CONFIG_HID_BPF is not set
>>> # end of HID-BPF support
>>> 
>>> #